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.

Food allergy series: FPIES (part 2)

FPIES is usually diagnosed clinically. Endoscopy and biopsy are not necessary to diagnose, but is sometimes done to rule out other conditions.

Scopes have shown a variety of inflammatory changes in the GI tract of FPIES kids. Diffuse colitis, friable mucosa, rectal ulceration and bleeding have been observed.  Increased levels of TNFa and decreased receptors for TGF-b have been found in the GI tract. Baseline intestinal absorption is usually normal.

Biopsies have shown villous atrophy, tissue edema, crypt abscesses, increased white blood cells, including eosinophils and mast cells, and IgM and IgA containing plasma cells. Radiology showed air fluid levels (collection of both fluid and gas in the intestines), narrowing and thickening of the mucosa in the rectum and sigmoid colon and thickening of the circular folds in the small intestine. When surgery has been performed, distension of the small bowel and thickening of the jejunum has been seen.

Food specific IgE is not usually present. In one study, 21% of patients with solid food FPIES had detectable food specific IgE. 18-30% with FPIES to cow’s milk or soy have IgE for it. If IgE is found, the course of FPIES is longer. One study found a decrease in food specific IgG4 in FPIES patients along with an increase in food specific IgA.

FPIES is managed by removing the offending food. Exclusive breastfeeding can be protective. If not breastfed, use of casein hydrolysate formula is recommended. Less commonly, amino acid formula or IV fluids may be needed. Doctors recommend introducing yellow vegetables and fruits as solids rather than cereal at six months of age. Grains, legumes and poultry should be avoided for the first year of life. Once tolerance is established to one food in a high risk category, like grains, the child is more likely to tolerate other foods in the same category.

Oral food challenges (OFC) should be undertaken to determine if tolerance to the food has been achieved. A conservative approach recommends challenges every 18-24 months in patients without recent symptoms. OFCs are high risk procedures for FPIES children. The following procedure should be observed:

  • Any FPIES OFC must be physician supervised. Generally, inpatient settings are preferred, but if an outpatient setting can provide appropriate supportive care, it may be acceptable. Intravenous access should be secured prior to beginning and IV fluids and medications should be immediately available in case of reaction. ICU care is not recommended unless there is a history of near fatal reactions.
  • Blood should be drawn immediately before beginning the OFC to provide baseline complete count count and neutrophil count.
  • Over the first hour, 0.06-0.6g/kg body weight of food protein should be administered in three equal doses. It should not exceed 3g of total protein or 10g of total food or 100ml of liquid for initial feeding.
  • If patient has no reaction, give a full serving of food as determined by their age.
  • Observe patient for several hours afterward.
  • In the event of reaction, administer 20 ml/kg boluses of normal saline.
  • In the event of severe reaction, including repetitive vomiting, profuse diarrhea, lethargy, hypotension or hypothermia, administer 1 mg/kg methylprednisolone intravenously, up to 60-80mg total. About 50% of patients who react to FPIES OFCs will need IV fluids and steroids.
  • Epinephrine must be available during FPIES OFCs for treatment of hypotension and shock. In FPIES cases, epinephrine does not resolve vomiting and lethargy.
  • In children with positive skin tests and/or food specific IgE, antihistamines should also be available during OFCs.
  • Blood should be drawn six hours after OFC to compare to baseline values. If patient has diarrhea, stool guaiac tests should be done, and stool samples should be tested for white bloods, red blood cells and eosinophils in feces.

An OFC is considered either positive or negative. Positive means there is a reaction. Negative means there is not. It is positive if the patient experiences vomiting, lethargy or diarrhea in an appropriate time frame. In the absence of symptoms, if the neutrophil count is over 3500/ul, or white blood cells, frank or occult blood, and/or eosinophils are present in feces, the challenge is still considered positive.  More than 10 leukocytes/hpf in gastric juice at the 3 hour mark has been suggested as a positive marker, but needs further investigation. In the study that noted this marker, gastric juice was obtained via orogastric feeding tubes.

One study looked at the resolution of FPIES over a ten year period. 160 subjects were included in the study. 54% were male. Median age of diagnosis was 15 months. 180 OFCs were done for 82 patients, of which 30% had obtained an FPIES diagnosis based on previous OFCs. 44% of patients reacted to cow’s milk; 41% to soy; 22.5% to rice; and 16% to oat. 65% had only one food sensitivity, 26% had two, and 9% had three or more. Most had some form of atopic disease and 39% had detectable food specific IgE. 24% had IgE specific for the food causative for their FPIES reaction. Of the patients with IgE for cow’s milk, 41% of them moved from an FPIES reaction type to an IgE allergy reaction type.

60% of FPIES cases resolve by three years of age. This finding is an average and different populations see much different results. In South Korea, 90% of patients resolve by three years of age. In the US, only 25% resolve by this age. The differences observed are thought to be due to other factors, such as the frequency of food specific IgE and atopic disease. The median age for FPIES resolution depended largely on the food: 4.7 years for rice, 4 years for oat, 6.7 years for soy, 5.1 years for milk. If milk IgE was present, the patient did not become tolerant of milk during the course of study.

FPIES overwhelmingly affects very young children. However, there are rare cases of older children and adults developing FPIES at a later age. These cases involve fish and shellfish as the offending foods.

 

References:

Leonard, Stephanie, Nowak-Wegrzyn, Anna. Food protein induced enterocolitis syndrome: an update on natural history and review of management. Ann Allergy Asthma Immunol. 2011; 107:95-101.

Caubet, Jean Christoph, et al. Clinical features and resolution of food protein induced enterocolitis syndrome : 10-year experience. J Allergy Clin Immunol. 2014; 134(2): 382-389.

 

Food allergy series: Risk factors for developing food allergies

There are a number of factors that seem to contribute to developing food allergies. Genetics seems to play an important role. One study found that that 64% of monozygotic twins had a concordance of peanut allergy, while only 7% dizygotic twins concorded. This means that in 64% of identical twin sets, either both had peanut allergies or neither did, while that was the case in only 7% of fraternal twins. Because monozygotic twins have identical genetic sequences, this finding implies a strong genetic component. HLA haplotyping has been studied, with conflicting reports on links between HLA type and allergies.

One of the most important genetic findings regards filaggrin, a skin barrier protein. Patients with a specific filaggrin mutation are more likely to develop peanut sensitization. This indicates that a damaged skin barrier could cause food sensitization and allergy, and further supports the idea that non-oral exposures can be sensitizing. Additionally, filaggrin mutation causes increased inflammatory mediators in the skin.

Generally, children with peanut or tree nut allergies react the first time the food is ingested. It is thought that they previously encountered these allergens in their environment. Household exposure to peanut was a significant risk factor for peanut allergy in infants. Peanut responsive T cells are found in the skin homing T cells in peanut allergic patients, implying that patients may first be exposed through the skin. There is not yet enough data on maternal ingestion of allergens to know if this is a risk factor. There are conflicting data sets on whether breastfeeding is protective against food allergies, and in any case, outcome appears to be dependent on the mother’s own sensitivity profile. Now seen in multiple recent studies, it seems that early oral exposure to food allergens may actually be protective against food allergy, a change from data produced over a decade ago.

Immune dysregulation is obviously involved in food allergies. Low vitamin A and vitamin D, which modulate the immune system, have been noted as risk factors. Interestingly, food allergy frequency varies with latitude, indicating a further possible connection to sun exposure and vitamin D deficiency. High fat diet can also change the composition and behavior of the microbial content of the GI microbiome. Medium chain triglycerides can increase sensitization when given along with food antigens in mice. There are mixed results with long chain fatty acids.

The changes in hygiene, cleaning products and use of antimicrobial compounds by the general public in the last decades have been implicated in many of the immune changes we have seen, including increasing autoimmune diseases and food allergies. This is known as the hygiene hypothesis, and it states that reduced exposure to microbes changes immune defense, causing improper reactivity to harmless components, like food and self cells. In food allergic mice, the gut microbiota has a very specific composition and transferring this flora set can actually make others more likely to develop food allergies. Dysbiosis has been noted in children with food allergies and a sequencing study demonstrated that food allergic children with atopic dermatitis have reduced microbial diversity in the gut.

 

References:

Cecilia Berin, Hugh A. Sampson. Food allergy: an enigmatic epidemic. Trends in Immunology, Volume 34, Issue 8, August 2013, pages 390-397.

Cecilia Berin, Hugh A. Sampson. Mucosal Immunology of Food Allergy. Current Biology, Volume 23, Issue 9, May 2013, pages R389-R400.

Food allergy series: Food related allergic disorders

The term “food allergy” is generally used by medical professionals to refer to IgE mediated allergic responses. However, it is used in a broader sense by patients who have similar conditions because the term is more likely to be understood. The truth is that there are several types of allergic disorders provoked by foods. They are all listed below and will be expounded upon in the coming days.

IgE antibodies mediate the following types of reactions. All of them have immediate onset of symptoms following interaction with the antigen.

  • Oral allergy syndrome. This presentation is usually mild. It causes itching and mild swelling in the mouth, progressing into the throat about 7% of the time, with less than 2% of cases progressing to anaphylaxis. OAS occurs due to sensitization to pollens. These pollens have specific shapes that are recognized by the IgE molecules; certain raw fruits and vegetables may shapes that are close enough to be recognized by the same IgE molecules. This is known as crossreactivity. Cooking the food changes the shapes seen by the IgE molecules and is therefore cooked forms are usually safe. In birch pollen sensitive people, apples, peaches, pears and carrots can cause crossreaction; in ragweed sensitive people, melons can be problematic. This is usually diagnosed by skin testing with the raw fruits/ vegetables. OAS can persist and be problematic during the season when the offending pollens are most prevalent.
  • Asthma irritation, including rhinitis. This can be caused by inhaling the food protein. It is most common in infants and children with the exception of work exposures in adults, like Baker’s asthma. This most commonly occurs with the eight major allergens: egg, milk, wheat, soy, peanut, tree nuts, fish and shellfish. Skin testing and serum IgE measurement can be used for diagnosis.
  • Urticaria and angioedema. This occurs when an offending food is ingested or contacts the skin (contact urticaria.) Food exposures cause 20% of acute urticaria cases and 2% of chronic urticaria cases. It is much more common in children and usually occurs after exposure to the eight major allergens. Skin testing and serum IgE measurement can be used for diagnosis.
  • GI hypersensitivity.Immediate onset vomiting can occur in response to the major food allergens. Skin testing and serum IgE measurement can be used for diagnosis.
  • Food associated, exercise induced anaphylaxis. This occurs following ingestion of food after recent completion of exercise. It is thought that exercise affects the way the GI tract absorbs and digests allergens. This most commonly affects adults, with wheat, shellfish and celery being the most common foods to provoke this reaction. Skin testing, serum IgE measurement, component testing and exercise testing can be used for diagnosis.
  • Delayed food-induced anaphylaxis to meat. This occurs several hours after ingesting the meat. It occurs when the body generates antibodies to carbohydrate a-Gal, which can be induced by tick bites. Beef, pork and lamb are known to cause reactions in a-Gal sensitive people. Testing should include serum IgE to a-Gal.
  • Anaphylaxis. I have addressed this in detail before. It can occur in response to any food, but the eight major allergens are most common. It results in massive mast cell degranulation, leading to cardiovascular collapse.

Some allergic responses to food are due to both IgE mediated reactions and delayed cell-mediated reactions.

  • Atopic dermatitis. In children with AD, about 35% of moderate/severe rashes are due to food reactions. This is thought to be due to food reactive T cells locating to the skin. It is most common in infants and least common in adults. All major allergens can be causative, but egg and milk are the most common. AD is usually self limiting. Skin testing and serum IgE measurement can be used for diagnosis.
  • Eosinophilic GI disease (EGID.) Eosinophils are inflammatory cells that share a lot of functions and behaviors with mast cells. Like mast cell disease, eosinophilic disease can affect a variety of organs, most commonly the GI tract. Symptoms are widely variable and related to level of inflammation and infiltration. It often causes difficult or painful swallowing, weight loss, obstruction and edema. EGID is related to the activity of several mediators, include IL-5, eotaxin, which causes eosinophils to home to various inflamed locations. Much like mast cell disease, it can occur in response to a wide array of foods. Elimination diets are first line treatments for EGID. Endoscopy, kin testing and serum IgE measurement can be used for diagnosis, but elimination diets are often used empirically for diagnosis.

Some allergic type responses to food are not due to IgE antibodies.

  • Food protein induced enterocolitis syndrome (FPIES.) Usually found in infants, repeat exposure to certain proteins causes chronic vomiting, diarrhea, low energy and poor growth. Exposure again following a period of abstinence from offending substance can cause vomiting, diarrhea and 15% drop in blood pressure. These reactions occur about two hours after ingestion. Cow’s milk, soy, rice and oat are the most frequently reported sources, but many others have been recorded. In FPIES children, their cells are more responsive to TNF-a and less responsive to TGF-b. FPIES usually resolves with age, but can be difficult to diagnose due to skin testing and serum IgE testing usually being negative.
  • Food protein induced allergic proctocolitis. This causes mucuosy, bloody stools as a result of eosinophilic response in infants. This occurs in response to milk through breast feeding and resolves when the substance is removed from the mother’s diet.
  • Heiner syndrome. This rare condition is marked by pulmonary infiltration, upper respiratory symptoms, iron deficiency anemia and failure to thrive. It occurs in infants and is triggered specifically by milk. It is thought that there may be a milk specific IgG reaction.
  • Celiac disease. This autoimmune disease causes malabsorption and enteropathy. It is a response to gliadin, a gluten protein in wheat and other grains. It can cause bone abnormalities, IgA deficiency, dermatitis herpetiformis and a variety of other complications. It can present at any age and is lifelong. Blood testing during food challenges, GI biopsies, and testing for HLA DQ2 and DQ8.

Cell mediated reactions are not due to IgE antibodies.

  • Allergic contact dermatitis. This type of eczema occurs in response to metals in foods. This occurs mainly in adults. It is diagnosed by atopy patch testing.

Mast cell reactions to food are related to inappropriate degranulation which has not been fully characterized. Mast cell food reactions will be discussed more completely in an upcoming post.

 

Reference:

Sicherer, Scott, Sampson, Hugh. Food allergy: Epidemiology, pathogenesis, diagnosis and treatment. J Allergy Clin Immunol 2014, 133 (2): 291-307.