February 2015: Post summaries and take home points

How to activate mast cells: Complement protein C3a

  • The complement system is part of the immune system. It allows infecting organisms to be more readily found and destroyed by the immune system.
  • Mast cells express a receptor for C3a, a fragment produced during activation of the immune system.
  • C3a is an anaphylatoxin. It participates in exaggerating the anaphylactic response.
  • C3a increases vascular permeability, causes smooth muscle contraction, and draws white blood cells to inflamed spaces.
  • In mucosal mast cells (GI mucosa), C3a inhibits histamine and TNF release.
  • In serosal mast cells (skin, peritoneum, respiratory tract), C3a induces degranulation when stimulated by IgE or IgG.
  • Inhaled allergens activate complement system in mucosa of respiratory tract, resulting in formation of C3a.
  • Tryptase can change C3 to C3a.

 

Corticotropin releasing hormone, cortisol and mast cells

  • The term HPA axis refers to the mechanisms by which the hypothalamus, pituitary gland and adrenal glands control each other.
  • The HPA axis regulates many things, including the stress response, immune modulation, emotions, sexuality and digestion.
  • The hypothalamus is in the brain. It turns signals from the nervous system into endocrine signals that allow changes by using hormones.
  • The hypothalamus makes corticotropin releasing hormone (CRH).
  • The pituitary gland makes and releases many hormones, including adrenocorticotropic hormone (ACTH), thyroid stimulating hormone, growth hormone and others.
  • When the pituitary gland receives signals from the hypothalamus, it releases these hormones.
  • CRH from the hypothalamus stimulates the pituitary to produce ACTH.
  • The adrenal glands make and release cortisol, epinephrine, norepinephrine and other molecules in response to hormones from the pituitary.
  • ACTH from the pituitary stimulates the adrenals to produce cortisol.
  • Cortisol tells the hypothalamus to stop releasing CRH and the pituitary to stop making ACTH.
  • Taking steroids regularly suppresses ACTH so your body stops making its own steroids. This is weaning steroids is important.
  • CRH is released in response to stress, such as anaphylaxis.
  • CRH can bind to mast cells and cause release of VEGF.
  • CRH is also released by mast cells.