C5a

Examples of C5a in the following topics:

• Macrophages

  • Monocytes may also migrate towards increasing concentrations of molecules produced by microorganisms themselves, by damaged tissues, or by the activation of the complement or clotting cascades which release bioactive peptides such as C5a.

• The Complement System

  • C5a is an important chemotactic protein, helping recruit inflammatory cells.
  • Both C3a and C5a have anaphylatoxin activity, directly triggering degranulation of mast cells, as well as increasing vascular permeability and smooth muscle contraction.

• Role of the Complement System in Immunity

  • Note that C5a has a number of other functions in the immune system, such as causing vasodilation during inflammation and stimulating neutrophil chemotaxis.

• Immune Complex Autoimmune Reactions

  • Activation of complement primarily results in cleavage of soluble complement proteins forming C5a and C3a, which activate recruitment of PMNs and local mast cell degranulation (requiring the binding of the immune complex onto FcγRIII), resulting in an inflammatory response.

• Type III (Immune Complex) Reactions

  • The cause of damage is as a result of the action of cleaved complement anaphylotoxins C3a and C5a, which, respectively, mediate the induction of granule release from mast cells (from which histamine can cause urticaria), and recruitment of inflammatory cells into the tissue (mainly those with lysosomal action, leading to tissue damage through frustrated phagocytosis by polymorphonuclear neutrophils and macrophages).