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mast cell biology

Circadian rhythm of mast cells

The circadian clock (also called circadian rhythm) regulates many physiological activities including the sleep-wake cycle, metabolism, digestion and immune processes. It is essentially a system that tells cells in the body what to do based on a 24 hour cycle, which can be influenced by such things as light cues, sleep and medication. Many cell types in the body have been shown to maintain their own internal circadian clocks and to change their behavior based upon time. Mast cells and eosinophils have been shown to maintain their own internal clocks.

On a cellular level, the circadian clock is maintained by the expression of clock genes. Inside the cell, a protein called CLOCK attaches to another protein (BMAL1) and they initiate expression of several genes that regulate circadian rhythm in the cell. These genes are called Period 1, Period 2, Period 3, Cryptochrome 1 and Cryptochrome 2. The proteins made by those genes regulate the expression of other genes based upon time.

An interesting facet of allergic disease is the well established variation in symptom severity depending on the time of day. This is seen in a variety of allergic conditions, such as asthma and atopic dermatitis. Allergic symptoms, including those that affect pulmonary function, are worse between midnight and morning, with a ramping up of symptoms seen around 10pm. This worsening overnight often results in sleep disruptions and “morning attacks”, which affect rest and result in decreased quality of life for patients. This has been verified repeatedly both through mouse studies and in reports of human patients.

Circadian rhythm has been shown to affect mediator release in mast cells, and this has been shown to be regulated by the five genes listed above. If even one of those genes are mutated, the mediator release becomes uniform and does not shown the peaks and lows observed normally. Both tryptase and plasma histamine levels have been observed to have lower levels in the afternoon and to peak at night. A marker associated with degranulation (b-hexosaminidase) showed the same pattern.

There is currently no information available on how mast cells tell time in relation to the rest of the body, though it is thought that mast cells receive molecular signals that “start the clock”. Importantly, in mice that have had their adrenal glands removed, mast cells do not shown circadian rhythms in mediator release. This indicates that the signal that “starts the clock” comes to mast cells from the adrenal glands. Corticosterone is being investigated as the possible signal, as it has been shown to induce expression of at least two clock genes, Period 1 and Period 2.

 

References:

Silver, A.C., Arjona, A., Hughes, M.E., Nitabach, M.N., Fikrig, E., 2012. Circadian expres-sion of clock genes in mouse macrophages, dendritic cells, and B cells. BrainBehav. Immun. 3, 407–413.

Smolensky, M.H., Lemmer, B., Reinberg, A.E., 2007. Chronobiology and chronother-apy of allergic rhinitis and bronchial asthma. Adv. Drug Deliv. Rev. 9–10,852–882.

Baumann, A., Gonnenwein, S., Bischoff, S.C., Sherman, H., Chapnik, N., Froy, O.,Lorentz, A., 2013. The circadian clock is functional in eosinophils and mast cells. Immunology 4, 465–474.

Burioka, N., Fukuoka, Y., Koyanagi, S., Miyata, M., Takata, M., Chikumi, H., Takane, H.,Watanabe, M., Endo, M., Sako, T., Suyama, H., Ohdo, S., Shimizu, E., 2010. Asthma: chronopharmacotherapy and the molecular clock. Adv. Drug Deliv. Rev. 9–10,946–955.

Cermakian, N., Lange, T., Golombek, D., Sarkar, D., Nakao, A., Shibata, S., Mazzoccoli, G., 2013. Crosstalk between the circadian clock circuitry and the immune system.Chronobiol. Int. 7, 870–888.

IgE-dependent activation of human mast cells and fMLP-mediatedactivation of human eosinophils is controlled by the circadian clockAnja Baumanna, Katharina Feilhauerb, Stephan C. Bischoffa, Oren Froyc, Axel Lorentza. Molecular Immunology 64 (2015) 76–81.

Yuki Nakamura, et al. Circadian regulation of allergic reactions by the mast cell clock in mice. J Allergy Clin Immunol 133 (2014) 568-575.

 

Allergic effector unit: The interactions between mast cells and eosinophils

Eosinophils are granulocytes that can localize to the tissues under certain conditions, including allergic response. Eosinophilic granules contain the positively charged proteins major basic protein, eosinophil peroxidase, eosinophil cationic protein, and eosinophil-derived neurotoxin. Like mast cells, eosinophils release these granules in response to many things, including inflammatory signals, parasitic infection, tissue damage and allergic inflammation. They express many receptors, including receptors for platelet activating factor (PAF) and histamine receptors. PAF and histamine are both released by mast cells.

Mast cells and eosinophils are overwhelmingly found together in late and chronic stages of allergic inflammation. They function in such close concert that mast cells, eosinophils and their effects have been termed the allergic effector unit (AEU). Mast cells release signals that affect eosinophil behavior and receive signals from eosinophils. These cells often also function while in physical contact with one another. When eosinophils are in physical contact with mast cells, they live longer than normal. CD48, 2B4, DNAM-1 and Nectin-2 are all involved in the mast cell – eosinophil contact mechanism.

Major basic protein can activate mast cells and eosinophil peroxidase is taken up by mast cells as a signaling molecule. Tryptase draws eosinophils to mast cells and causes release of eosinophil peroxidase, IL-6 and IL-18 from eosinophils. Histamine and prostaglandin D2 also signal eosinophils to migrate towards mast cells. Mast cell secreted eotaxin activates eosinophils by the histamine 4 (H4) receptor. Both cell types secrete leukotrienes and both express leukotriene receptors.

When grown together, researchers are able to investigate the behavior of mast cells and eosinophils together. This is called co-culture. In 29% of cases, eosinophils will migrate towards resting (non-activated) mast cells. In 45% of cases, eosinophils will migrate towards IgE activated mast cells. In 47% of cases, eosinophils will migrate towards mast cells activated through a non-IgE pathway. The specific attractant signal has not been identified.

When co-cultured with eosinophils, basal mast cell mediator release was 5% higher. When the mast cells were activated by IgE, degranulation was 15% higher. In order to activate mast cells, eosinophils must be in contact with them. However, mast cells can activate eosinophils without contact. In co-cultures with mast cells, eosinophil peroxidase constituted 47% of eosinophil released proteins, compared with 18% normally.

In low term co-cultures, both mast cells and eosinophils stayed activated. TNF was high in the co-culture, but not IL-6, IL-8 and IL-10. Importantly, low relative numbers of mast cells could activate eosinophils, but mast cell activation was most effective when eosinophils were more numerous. Eosinophils are thought to reduce the threshold of mast cell responsiveness to IgE.

 

References:

Elishmereni M, Bachelet I, Nissim Ben Efraim AH, Mankuta D, Levi-Schaffer F. Interacting mast cells and eosinophils acquire an enhanced activation state in vitro. Allergy 2013; 68: 171–179.

Elishmereni M, Alenius HT, Bradding P, Mizrahi S, Shikotra A, Minai-Fleminger Y, et al. Physical interactions between mast cells and eosinophils: a novel mechanism enhancing eosinophil survival in vitro. Allergy 2011;66:376–385.

Minai-Fleminger Y, Elishmereni M, Vita F, Soranzo MR, Mankuta D, Zabucchi G et al. Ultrastructural evidence for human mast cell-eosinophil interactions in vitro. Cell Tissue Res 2010;341:405–415.

Puxeddu I, Ribatti D, Crivellato E, Levi- Schaffer F. Mast cells and eosinophils: a novel link between inflammation and angiogenesis in allergic diseases. J Allergy Clin Immunol 2005;116:531–536.

Mast cell mediators: Sphingosine-1-phosphate

Sphingosine-1-phosphate (S1P) is a lipid mediator involved in many processes, including development of vessels, vascular permeability, and immune function. It is found in the blood, often bound with proteins such as high density lipoprotein (HDL, “good cholesterol”). Receptors for S1P are found on many cell types.

Activation of the high affinity receptor for IgE causes production of S1P by mast cells. This may also affect the expression and activation of S1P receptors. Mast cells then secrete S1P into the surrounding space.  Mast cells also have receptors to bind S1P.

The S1P1 receptor helps to direct mast cells to sites of inflammation, but does not influence degranulation. The S1P2 receptor deters from localizing to sites of inflammation but enhances degranulation once they have migrated. S1P is known to increase during acute tissue inflammation, in airways following asthmatic challenge and in joints of rheumatic patients. S1P may be responsible for the accumulation of immune cells in such places, but the exact nature of this role is unclear.

S1P receptors regulate the vascular system, including heart rate and permeability.  S1P2 receptor makes vessels more permeable and regulates blood flow to various organs. S1P2 receptor is involved in counteracting the vasodilation effect of histamine (and thus low blood pressure). Histamine can stimulate S1P production.

S1P can also cause bradycardia and high blood pressure via the S1P3 receptor.  I am curious to know if S1P is involved in the high blood pressure type of anaphylaxis some people have.

In models where the genes for making S1P have been deleted, recovery from anaphylaxis is delayed, with severe hypotension. However, in mice with S1P2 receptors, injecting S1P could rescue mice from anaphylaxis. For this reason, molecules that can act on the S1P receptors are being investigated as possible drug targets to produce an alternative to epinephrine.

 

References:
Olivera A, Rivera J. An emerging role for the lipid mediator sphingosine-1-phosphate in mast cell effector function and allergic disease. Adv Exp Med Biol. 2011; 716: 123–142.

Allende ML, Proia RL. Sphingosine-1-phosphate receptors and the development of the vascular system. Biochim Biophys Acta. 2002;1582:222–227.

Olivera A, Eisner C, Kitamura Y, et al. Sphingosine kinase 1 and sphingosine-1-phosphate receptor 2 are vital to recovery from anaphylactic shock. J Clin Invest. 2010 “in press”.

Allergic to infections: Other behaviors of toll like receptors

I posted earlier this week about Toll-like receptors (TLRs). These are receptors on the outside of mast cells (and other cells) that tell them there is an infection. Instead of only being able to bind very specific molecules like receptors often do, these TLRs are able to bind lots of molecules that look alike. Once these are bound, it tells mast cells to activate, make mediators and release them.

After TLR2, TLR4 is the most well understood Toll-like receptor. Molecules that bind TLR4 are from infectious gram negative bacteria, several viruses (including RSV), Cryptococcus neoformans, and Candida albicans. It also binds fibrinogen, which is involved in the clotting cascade, and nickel. When infected with a gram negative bacteria, like E. coli or Ps. aeruginosa, mast cells secrete inflammatory molecules TNF, IL-6, IL-13, and IL-1b.

TLR4 also has a very intriguing behavior with opioid receptors on mast cells. These opioid receptors are the binding sites for opiate medications, like morphine, which are common triggers for mast cell patients. One study found that treatment with morphine actually interferes with TLR4 making inflammatory molecules. Other studies have found that opiates can bind TLR-4 directly. When bound, TLR-4 signals for release of TNFa, CCL1 and IL-5.

Other TLRs on mast cells can be bound by various molecules and produce and release mediators in return. TLR3 is bound by viral proteins and induces release of interferon a and b; TLR5 binds proteins from some flagellated bacteria and releases TNF and IL-1b; TLR9 binds unmethylated DNA of the type released by bacteria and DNA viruses, and releases interferon a, TNF, IL-1b and leukotrienes.

All TLR receptors can function independently of IgE. This is one example of an IgE independent pathway, or a way mast cells can degranulate or secrete mediators without IgE.

 

References:

Hilary Sandig and Silvia Bulfone-Paus. TLR signaling in mast cells: common and unique features. Front Immunol. 2012; 3: 185.

Abraham S. N, St John A. L. (2010). Mast cell-orchestrated immunity to pathogens. Nat. Rev. Immunol. 10440–452.

Dietrich N., Rohde M., Geffers R., Kroger A., Hauser H., Weiss S., Gekara N. O. (2010). Mast cells elicit proinflammatory but not type I interferon responses upon activation of TLRs by bacteria. Proc. Natl. Acad. Sci. U.S.A.1078748–8753

Gilfillan A. M., Tkaczyk C. (2006). Integrated signalling pathways for mast-cell activation. Nat. Rev. Immunol.6218–230.

Fehrenbach K., Port F., Grochowy G., Kalis C., Bessler W., Galanos C., Krystal G., Freudenberg M., Huber M. (2007). Stimulation of mast cells via FcvarepsilonR1 and TLR2: the type of ligand determines the outcome. Mol. Immunol. 442087–2094.

McCurdy,J.D., Olynych,T.J., Maher, L. H.,and Marshall, J.S.(2003). Cutting edge: distinct Toll-like receptor2 activators selectively induce different classes of mediator production from human mast cells. J. Immunol. 170, 1625–1629.

Medina-Tamayo, J., Ibarra-Sanchez, A., Padilla-Trejo,A., and Gonzalez- Espinosa, C. (2011). IgE-dependent sensitization increases responsiveness to LPS but does not modify development of endotoxin tolerance in mast cells. Inflamm. Res. 60, 19–27.

Qiao,H., Andrade,M.V., Lisboa,F. A., Morgan,K., and Beaven, M. A. (2006).FcepsilonR1 and toll-like receptors mediate synergistic signals to markedly augment production of inflammatory cytokines in murine mast cells. Blood 107, 610–618.

Yoshioka,M., Fukuishi,N., Iriguchi,S., Ohsaki, K., Yamanobe,H., Inukai, A., Kurihara,D., Imajo,N., Yasui, Y., Matsui, N., Tsujita, T., Ishii, A., Seya,T., Takahama,M., and Akagi, M. (2007). Lipoteichoicacid down- regulates FcepsilonRI expressionon human mast cells through Toll-like receptor2. J. Allergy Clin. Immunol. 120, 452–461.

Varadaradjalou, S., Feger, F., Thieblemont, N., Hamouda, N.B., Pleau, J. M., Dy,M., and Arock, M. (2003). Toll-likereceptor2 (TLR2)and TLR4 differentially activate human mast cells. Eur. J. Immunol. 33, 899–906.

Allergic to infections: How bacteria, viruses and fungi activate mast cells

I am often asked about whether an infection, even a mild cold, can cause worsening mast cell symptoms.  The answer is yes.  Viral, fungal and bacterial infections can all cause mast cell activation, and patients with prior activated mast cells are especially susceptible.  This is why it is so important for mast cell patients to avoid contagious illness as much as possible.

Several cell types in the human body have Toll-like receptors (TLRs) on their cell surfaces. These receptors bind many types of molecules that indicate presence of infection. These molecules are called pathogen-associated molecular patterns (PAMPs) and they share similar shapes that identify them as being released by infecting organisms. When these PAMPs are bound by TLRs on cell surfaces, it sends signals for the cells to mount an immune response.

The expression of TLRs on mast cells has been well studied using both mouse (murine) and human mast cells. TLR1, 2, 3, 4, 5, 6, 7, 9 and 10 have been identified on mast cells by at least one study. Some of these TLRs were only detected by finding related mRNA. (When cells express a gene to make a protein like a TLR, the DNA gene is copied into mRNA, which tells the cell how to make the TLR.) Since only the mRNA and not the TLR was directly identified, these TLRs require more research to be fully characterized.

TLR2 is one of the most well studied and understood of toll-like receptors found on mast cell surfaces. TLR2 is also known as CD282. Substances that bind to TLR2 include many molecules released by bacteria and fungi. Several types of peptidoglycans and found in bacterial cell membranes bind TLR2. In particular, lipoteichoic acid is a potent activator of TLR2. This molecule is found on the surfaces of gram-positive bacteria, like Staphylococcus spp. (Staph, MRSA) and Streptococcus spp. (Strep). Other bacteria that are known to activate TLR2 include Neisseria meningitides, Haemophilus influenzae, and Borrelia burgdorferi, among others. Mycobacteria are also activating to TLR2. Zymosan is found in cell membranes of yeast and binds TLR2. Aspergillus fumigatus (fungi) and several viruses, including Herpes simplex, Varicella zoster, Cytomegalovirus and measles, activate TLR2 responses. Heat shock protein 70 (HSP 70) is released by cells in the body when they are under certain types of stress, and this can activate TLR2.

When TLR2 is bound, mast cells produce and release several types of molecules that are not prestored in granules. The molecules released depend on which protein has bound TLR2. These molecules include IL-1b, which causes inflammatory pain hypersensitivity; IL-5, which activates eosinophils; leukotriene B4, which forms reactive oxygen species and participates in inflammation; leukotriene C4, which causes slow contraction of smooth muscle, including in the airway; GM-CSF (Granulocyte macrophage colony-stimulating factor), a growth factor for white blood cells; TNF, which has many inflammatory effects; RANTES, which brings other white cells to the site of inflammation; and others. TLR2 activation is responsible for the worsening of asthma symptoms in the presence of bacterial infection.

Multiple studies reported that stimulation of TLR2 with peptidoglycan (a constituent of gram positive bacterial cell membranes) induced degranulation. Stimulation with peptidoglycan induced histamine release as well as cytokine release in a 2003 study (Varadaradjalou 2003). Another study found that peptidoglycan did not cause statistically significant degranulation, but zymosan (a fungal product) and Pam3Cys (a synthetic molecule that acts like LPS, another component of bacterial membranes) did induce significant degranulation (McCurdy 2003). Other studies have not been able to replicate these results.

There is also evidence that stimulation of TLR2 can change the behavior of mast cells. When mast cells are grown in the presence of bacterial cell membrane products, they make different amounts of different proteins. Another study demonstrated that two bacterial cell membrane products downregulated the amount of FceRI (the IgE receptor) on the surface of mast cells, so after two days, mast cells were less responsive to stimulation by IgE molecules. This was partially due to the effects of TLR2 (Yoshioka 2007).

However, mast cells that are sensitized react more strongly to TLR2 activation with LPS (Medina-Tamayo 2011). This effect seems to be reliant on prior binding of IgE. Other very technical studies have investigated the effect of antigen (such as bacterial, viral or fungal products) on the interplay between the IgE receptor and TLR receptors.   While most of this work has been done in mouse cells, several investigators have shown that activation of TLR receptors and the IgE receptor causes enhanced release of cytokines but not degranulation. It is thought that the exaggerated response to IgE receptor and TLR2 stimulation can cause the exacerbation of allergic type conditions during active infection. (Qiao 2006)

 

References:

Hilary Sandig and Silvia Bulfone-Paus. TLR signaling in mast cells: common and unique features. Front Immunol. 2012; 3: 185.

Abraham S. N, St John A. L. (2010). Mast cell-orchestrated immunity to pathogens. Nat. Rev. Immunol. 10440–452.

Dietrich N., Rohde M., Geffers R., Kroger A., Hauser H., Weiss S., Gekara N. O. (2010). Mast cells elicit proinflammatory but not type I interferon responses upon activation of TLRs by bacteria. Proc. Natl. Acad. Sci. U.S.A.1078748–8753

Gilfillan A. M., Tkaczyk C. (2006). Integrated signalling pathways for mast-cell activation. Nat. Rev. Immunol.6218–230.

Fehrenbach K., Port F., Grochowy G., Kalis C., Bessler W., Galanos C., Krystal G., Freudenberg M., Huber M. (2007). Stimulation of mast cells via FcvarepsilonR1 and TLR2: the type of ligand determines the outcome. Mol. Immunol. 442087–2094.

McCurdy,J.D., Olynych,T.J., Maher, L. H.,and Marshall, J.S.(2003). Cutting edge: distinct Toll-like receptor2 activators selectively induce different classes of mediator production from human mast cells. J. Immunol. 170, 1625–1629.

Medina-Tamayo, J., Ibarra-Sanchez, A., Padilla-Trejo,A., and Gonzalez- Espinosa, C. (2011). IgE-dependent sensitization increases responsiveness to LPS but does not modify development of endotoxin tolerance in mast cells. Inflamm. Res. 60, 19–27.

Qiao,H., Andrade,M.V., Lisboa,F. A., Morgan,K., and Beaven, M. A. (2006).FcepsilonR1 and toll-like receptors mediate synergistic signals to markedly augment production of inflammatory cytokines in murine mast cells. Blood 107, 610–618.

Yoshioka,M., Fukuishi,N., Iriguchi,S., Ohsaki, K., Yamanobe,H., Inukai, A., Kurihara,D., Imajo,N., Yasui, Y., Matsui, N., Tsujita, T., Ishii, A., Seya,T., Takahama,M., and Akagi, M. (2007). Lipoteichoicacid down- regulates FcepsilonRI expressionon human mast cells through Toll-like receptor2. J. Allergy Clin. Immunol. 120, 452–461.

Varadaradjalou, S., Feger, F., Thieblemont, N., Hamouda, N.B., Pleau, J. M., Dy,M., and Arock, M. (2003). Toll-likereceptor2 (TLR2)and TLR4 differentially activate human mast cells. Eur. J. Immunol. 33, 899–906.

Diabetes, steroids and hypoglycemia

Following alloxan induction of diabetes, rats overexpress glucocorticoids. This in turn depletes the mast cell populations in the skin, lungs and intestines. Glucocorticoids interfere with production and expression of tissue cytokines and stem cell factor, a growth factor for mast cells.

Several experiments have definitively proven that these steroids are responsible for downregulating mast cell growth and activity. Treating diabetic rats with the steroid receptor blocker RU486 or removing adrenal glands on both sides of the animal causes an increase in intestinal mast cell numbers and IgE formation.

The mechanism by which steroids confer these effects is thought to involve insulin. Glucocorticoids inhibit secretion of insulin in the pancreas. In turn, insulin release decreases systemic glucocorticoids. Additionally, insulin also activates mast cell signaling pathways. In the presence of insulin, antigen induced mast cell degranulation and survival is upregulated. In diabetic rats, administration of insulin recruits mast cells and increases response to antigen. Insulin treatment can reverse the reductions in mast cell populations, histamine production and IgE release seen following alloxan administration.

Increased activity of the HPA axis is often seen in type I and II diabetics, resulting in elevated cortisol. One study showed that appropriate activity can be restored with insulin treatment. This is achieved by a complex mechanism in which expression of glucocorticoid receptor mRNA is elevated in the pituitary, facilitating glucocorticoids to suppress expression of ACTH release.

 

Can hypoglycemia cause mast cell degranulation?

Yes. Activation of histamine 1 and 2 receptors as a result of insulin or hypoglycemia causes release of ACTH. Hypoglycemia (low blood sugar, which can also be induced after administration of insulin) normally increases ACTH levels in the blood. However, higher than normal histamine levels in the blood can interfere with the action of ACTH, which would normally address hypoglycemia via production of glucocorticoids. One study found that this effect can be mostly ameliorated by pretreating with antihistamines, though I suspect in mast cell patients, this may not achieve the full response seen in non-mast cell patients.

 

Can anaphylaxis cause hypoglycemia?

Yes. In instances of severe stress (emotional or physical), corticotropin-releasing hormone (CRH), neurotensin and substance P are released. Among other things, CRH can induce mast cell degranulation (of note, CRH does not directly induce histamine release via degranulation). CRH also causes increased expression of the IgE receptor on mast cells, which increases the likelihood of being stimulated and thus degranulation (this may cause histamine release). In tandem, neurotensin and substance P increases the expression of the CRHR-1 receptor for CRH on mast cells so that they are more sensitive to CRH. Likewise, neurotensin and substance P act on mast cells via receptors to induce degranulation (this causes histamine release). As a result of this degranulation, histamine and other mediators are present to inhibit the action of ACTH, which would otherwise increase blood sugar (via the production of cortisol, epinephrine, and norepinephrine).

 

References:

Carvalho V.F., Barreto E.O., Diaz B.L. et al. (2003) Systemic anaphylaxis is prevented in alloxan-diabetic rats by a mechanism dependent on glucocorticoids. Eur. J. Pharmacol. 472, 221–227.

Carvalho V.F., Barreto E.O., Cordeiro R.S. et al. (2005) Mast cell changes in experimental diabetes: focus on attenuation of allergic events. Mem. Inst. Oswaldo Cruz 100(Suppl. 1), 121–125.

Foreman JC, Jordan CC, Piotrowski W. Interaction of neurotensin with the substance P receptor mediating histamine release from rat mast cells and the flare in human skin. Br J Pharmacol. 1982 Nov;77(3):531-9.

Meng, Fanyin, et al. Regulation of the Histamine/VEGF Axis by miR-125b during Cholestatic Liver Injury in Mice. The American Journal of Pathology, Volume 184, Issue 3, March 2014, Pages 662–673

Theoharides, T., et al. A probable case report of stress-induced anaphylaxis. Ann Allergy Asthma Immunol xxx (2013) 1e2

Kjaer A, et al. Insulin/hypoglycemia-induced adrenocorticotropin and beta-endorphin release: involvement of hypothalamic histaminergic neurons. Endocrinology. 1993 May;132(5):2213-20.

Carvalho V.F, et al. Reduced expression of IL-3 mediates intestinal mast cell depletion in diabetic rats: role of insulin and glucocorticoid hormones. Int. J. Exp. Path. (2009), 90, 148–155.

Carvalho V.F, et al. Suppression of Allergic Inflammatory Response in the Skin of Alloxan-Diabetic Rats: Relationship with Reduced Local Mast Cell Numbers. Int Arch Allergy Immunol 2008;147:246–254.

Carvalho VF, Barreto EO, Diaz BL, Serra MF, Azevedo V, Cordeiro RS, et al: Systemic anaphylaxis is prevented in alloxan-diabetic rats by a mechanism dependent on glucocorticoids. Eur J Pharmacol 2003; 472: 221–227.

S.C. Cavalher-Machado, et al. Down-regulation of mast cell activation and airway reactivity in diabetic rats: role of insulin. Eur Respir J 2004; 24: 552–558.

Diabetes, mast cells and allergic disease

Patients with either type I or II diabetes mellitus demonstrate unusual physiology pertaining to hypersensitivity and mast cell activation. This was first described in 1962, when a paper reported that diabetic animals do not experience anaphylactic shock.   Despite the amount of time that has passed, the reasons for this are still being unraveled.

The role of mast cells in type II diabetes mellitus is more straightforward. When mice are made obese through dietary manipulation, they normally develop glucose intolerance or insulin resistance. If the mice are mast cell deficient, they do not develop these conditions. Transfer of mast cells to mast cel deficient mice was shown to reverse this protection against these complications.

In mice without established type Ii diabetes that were given manipulated diets to induce obesity, treatment with mast cell stabilizers actually prevented the development of type II diabetes. In mice with pre-established type II diabetes, treatment with mast cell stabilizers cromolyn or ketotifen protected against glucose intolerance and insulin resistance. These findings have been replicated in at least one patient, a type II diabetic who had normalized plasma glucose and A1C after six months on cromolyn.

The relationship between mast cells and type I diabetes is far more intricate.   This is mostly understood through a diabetic rat model. It is possible to induce type I diabetes in rats by administering a chemical called alloxan. Triggering diabetes in this way causes a variety of mast cell changes in these animals. The same changes can be seen when causing diabetes via administration of another chemical, streptozotocin.

Diabetic rats have less vascular response to the action of histamine and reduced mast cell degranulation. These animals are resistant to both local and systemic allergic responses, including anaphylaxis.   Mast cell populations become depleted and less likely to activate. When exposed to antigen, diabetic rats have 50% less degranulated mast cells and histamine release compared to non-diabetic controls.

IgE production is also suppressed in diabetic rats, both antigen specific IgE and total IgE. If you transfer mast cells from the spleen and lymph nodes of non-diabetic rats to diabetic rats, IgE production is diminished. Likewise, if mast cells from diabetic rats are transferred into non-diabetic animals, IgE production is restored.

This protection from allergic processes is well established in animals, but also translates to humans. Children with type I diabetes, and their siblings, are less likely to develop asthma. The incidence of bronchial asthma, rhinitis, and atopic dermatitis is lower than predicted in patients with diabetes mellitus.   Risk of death due to anaphylactic shock is significantly reduced in diabetes. This has been attributed to both the depletion of mast cell populations in diabetics, but also to the overproduction of corticosteroids in the body.

 

References:

Carvalho V.F., Barreto E.O., Diaz B.L. et al. (2003) Systemic anaphylaxis is prevented in alloxan-diabetic rats by a mechanism dependent on glucocorticoids. Eur. J. Pharmacol. 472, 221–227.

Carvalho V.F., Barreto E.O., Cordeiro R.S. et al. (2005) Mast cell changes in experimental diabetes: focus on attenuation of allergic events. Mem. Inst. Oswaldo Cruz 100(Suppl. 1), 121–125.

Foreman JC, Jordan CC, Piotrowski W. Interaction of neurotensin with the substance P receptor mediating histamine release from rat mast cells and the flare in human skin. Br J Pharmacol. 1982 Nov;77(3):531-9.

Meng, Fanyin, et al. Regulation of the Histamine/VEGF Axis by miR-125b during Cholestatic Liver Injury in Mice. The American Journal of Pathology, Volume 184, Issue 3, March 2014, Pages 662–673

Theoharides, T., et al. A probable case report of stress-induced anaphylaxis. Ann Allergy Asthma Immunol xxx (2013) 1e2

Kjaer A, et al. Insulin/hypoglycemia-induced adrenocorticotropin and beta-endorphin release: involvement of hypothalamic histaminergic neurons. Endocrinology. 1993 May;132(5):2213-20.

Carvalho V.F, et al. Reduced expression of IL-3 mediates intestinal mast cell depletion in diabetic rats: role of insulin and glucocorticoid hormones. Int. J. Exp. Path. (2009), 90, 148–155.

Carvalho V.F, et al. Suppression of Allergic Inflammatory Response in the Skin of Alloxan-Diabetic Rats: Relationship with Reduced Local Mast Cell Numbers. Int Arch Allergy Immunol 2008;147:246–254.

Carvalho VF, Barreto EO, Diaz BL, Serra MF, Azevedo V, Cordeiro RS, et al: Systemic anaphylaxis is prevented in alloxan-diabetic rats by a mechanism dependent on glucocorticoids. Eur J Pharmacol 2003; 472: 221–227.

S.C. Cavalher-Machado, et al. Down-regulation of mast cell activation and airway reactivity in diabetic rats: role of insulin. Eur Respir J 2004; 24: 552–558.

 

How to activate mast cells: Complement protein C3a

The complement system is part of the innate immune system. It is composed of many small proteins that circulate as inactive precursor molecules. When the immune system is triggered, enzymes cleave these precursors to form activate cytokines. These cytokines then cleave other precursors to form even more cytokines. This is known as a cascade and it amplifies the inflammatory signal to draw other inflammatory cells and molecules.

Mast cells express many receptors on their surfaces. The one people are most familiar with is the IgE receptor, also called FceRI. One of the receptors mast cells express is for C3a, a fragment of complement protein C3. This fragment is produced by the complement activation cascade. C3a is known for inducing smooth muscle contraction, increasing vascular permeability, recruiting white blood cells to the site of skin injection, and attracting macrophages, neutrophils, some lymphocytes, basophils and mast cells.

Something I haven’t touched on much is the fact that there are two major categories of mast cells in the body. Mucosal mast cells live in the GI mucosa. Serosal mast cells live in the skin, peritoneum and respiratory tract. These two populations have different mediators in their granules and respond differently to stimuli like C3a. In mucosal mast cells, C3a actually inhibits histamine and TNF release. In serosal mast cells, C3a increases degranulation of cells stimulated by IgE or IgG.

C3a has also been shown to cause expression of particular genes in mast cells that participate in production of cytokines. This is achieved by multiple pathways, one that works at low concentrations of C3a (cell surface GPCR) and one that works at higher concentrations (activation of G proteins).

In patients with allergic asthma, inhaled allergens like dust, dust mites, Aspergillus and ragweed pollen, activate the complement system in the mucosa of the respiratory tract. This generates the formation of C3a. Cells around mast cells release enzymes that can cleave C3 to form C3a. When mast cells become activated, they release a number of enzymes that may also cleave C3 to form C3a. Tryptase has been shown to do this in vitro, meaning in a reaction outside of the body.

When some receptors are stimulated too often, they become desensitized. This causes a signal to be sent into the cell that makes the cell internalize the receptor, or literally remove it from the surface so it can’t be activated anymore. This is the case for mast cell C3a receptors. I am curious to know if C3a receptors in mast cell patients don’t get desensitized. In theory, this would result in huge, fast allergic reactions without IgE stimulation and chronic activation of the inflammatory response. This has not been investigated to my knowledge.

Several mast cell mediators, including histamine, make blood vessels more permeable. Some researchers hypothesize that this action works to draw C3 to the activated mast cells. C3 can then be cleaved by tryptase, producing C3a, and amplifying the allergic reaction. Due to its well characterized role in anaphylaxis and allergic response, C3a is known as an anaphylatoxin.

 

References:

Erdei et al. Regulation of mast cell activation by complement-derived peptides. Immunology Letters 92 (2004) 39–42.

Ali H. Regulation of human mast cell and basophil function by anaphylatoxins C3a and C5a. Immunology Letters 128 (2010) 36–45.

M.R. Woolhiser, K. Brockow, D.D. Metcalfe. Activation of human mast cells by aggregated IgG through FcγRI: additive effects of C3a, Clin. Immunol. 110 (2004) 172–180.

T.C. Theoharides et al. Mast cells and inflammation. Biochimica et Biophysica Acta 1822 (2012) 21–33.

Lesser known mast cell mediators (Part 6)

Granulocyte macrophage colony-stimulating factor (GM-CSF) is a growth factor for white blood cells. It induces stem cells to make granulocytes (neutrophils, eosinophils, basophils, mast cells) and monocytes. The molecule activates STAT5, a protein that initiates gene expression. It is found at high levels in the joints of rheumatoid arthritis patients.

Fibroblast growth factor 2 (FGF2, also known as basic fibroblast growth factor, bFGF) is involved in angiogenesis, proliferation and wound healing. FGF2 binds heparin. It is thought that during wound healing, heparin degrading enzymes activate FGF2, driving the development of new blood vessels.

Neutrophin 3 is a nerve growth factor that regulates the survival and growth of neurons and synapses.

Nerve growth factor (NGF) regulates neuron survival and axonal growth. In its absence, neurons undergo apoptosis. It has been found to induce ovulation in some mammals. NGF is often elevated in inflammatory conditions as it suppresses inflammation. Children with autism sometimes have high levels of NGF in their cerebral spinal fluid. Low levels of NGF are seen in metabolic syndromes, type 2 diabetes and obesity.

Platelet derived growth factor (PDGF) is a growth factor that participates in blood vessel growth. It is a required factor for the division of fibroblasts, connective tissue cells important in wound healing.

Nitric oxide (NO, also endothelium derived relaxing factor, EDRF) is a cell signaling molecule and potent vasodilator. It is a precursor to nitroglycerin. It is produced by several nitric oxide synthase enzymes. NO maintains blood vessels by preventing vascular muscle contraction and aggregation of cells on the endothelium. NO has a well described variety of activities.

Leukotriene B4 is a cell signaling molecule. It facilitates the transition of white blood cells from the endothelium into tissues. It also forms reactive oxygen species.

Leukotriene C4 is one of the components of the slow reacting substance of anaphylaxis (SRS-A). It is secreted during anaphylaxis and contributes to the inflammatory processes. It causes prolonged, slow contraction of smooth muscle and bronchoconstriction. It is 5000x more potent than histamine in this capacity but acts more slowly and lasts longer.

Platelet activating factor (PAF) mediates a variety of immune activities, including various inflammatory processes and anaphylaxis. It is also a vasodilator and bronchoconstrictor. At high concentrations, PAF can cause severe airway inflammation to such degree as to be life threatening.

 

All mediators listed here are produced by mast cells upon stimulation and are not stored in granules.

Lesser known mast cell mediators (Part 5)

Interleukin-16 (IL-16) is a cytokine that attracts several types of cells that express the CD-4 receptor on their surfaces, including monocytes, eosinophils and dendritic cells. It acts by binding to the CD-4 receptor. IL-16 was previously known as lymphocyte chemoattractant factor (LCF).

Interleukin-18 (IL-18) is a cytokine with several defined functions. Working with IL-12, it triggers a cell-mediated immune response after infection. It causes natural killer (NK) cells and some types of T cells to release interferon-γ, and for this reason is sometimes called interferon-γ inducing factor. This interferon activates macrophages and other cell types. IL-18 and IL-12 can inhibit production of IgE and IgG1 when mediated by IL-4. IL-18 causes severe inflammatory reactions and has been implicated in various diseases. In adenomyosis patients, more IL-18 receptors are found in the endometrium. It is one of the molecules responsible for Hashimoto’s thyroiditis. It also increases production of amyloid-beta in neuron cells, which is associated with Alzheimer’s disease.

Macrophage migration inhibitory factor (MIF) is an inflammatory cytokine that stimulates an acute immune response by binding to CD74. MIF level is associated with severity of rheumatoid arthritis. Glucocorticoids (steroids) stimulate white cells to release MIF.

Transforming growth factor beta (TGF-β) is secreted by mast cells and participates in the pathology of many diseases, including bronchial asthma, heart disease, diabetes, lung fibrosis, telangiectasia, Marfan syndrome, vascular Ehlers Danlos syndrome, Parkinson’s disease, chronic kidney disease, multiple sclerosis, AIDS, among others. (Note: I suspect that one of the links between mast cell disease and EDS is this molecule. Its signaling affects differentiation and regulation of vascular tissues and connective tissues. In a mouse model of Marfan syndrome, a connective tissue disorder, the characteristic Marfan features can be alleviated by administering a TGF- β blocker.)

Tumor necrosis factor (TNF-α) is part of a family of cytokines that cause apoptosis, cell death. It is an adipokine that participates in both general inflammation and the acute phase inflammatory response. It is produced by mast cells as well as many other cell types, including neutrophils, eosinophils and neurons, among others. TNF regulates immune cells, causes fever, weight loss, fatigue and tumor destruction. This molecule is dysregulated in several diseases, including several cancers, severe depression, IBD, Alzheimer’s and rheumatoid arthritis.

Macrophage inflammatory protein 1α (MIP-1α, chemokine ligand 3, CCL3) causes acute inflammation and recruitment of other white blood cells.

Stem cell factor (SCF) is a cytokine that binds to the CD117, better known as CKIT, receptor on mast cells. SCF regulates the mast cell life cycle, telling them when to make new cells and when to die. In CKIT+ mast cell patients, the CKIT receptor is misshapen so the cell mistakenly thinks SCF is bound to the receptor all the time. It also induces histamine release.

 

All mediators listed here are produced by mast cells upon stimulation and are not stored in granules.