Depending on their structre and function there are five types of antibodies
IgG – Highest concentration in serum and excellent penetration into tissues. Can cross the placenta by week 16 of pregnancy. Fixes complement.
IgA – Most important antibody for host defense at mucosal surfaces (sites of antigen entry). Produced locally and often present in a modified form in secretions such as tears and salvia (secretory IgA). Secretory IgA is more resistant to enzymatic degradation.
IgM – The first class of antibody made in the primary response to antigen. Vigorously fixes complement and is very important in host defense against blood-borne antigens.
IgD – Functions mainly as an antigen receptor on B cells that have not been exposed to antigens. It has been shown to activate basophils and mast cells to produce antimicrobial factors.
E – IgE – Binds to the surface of mast cells and basophils, and when cross-linked, results in release of granular contents (primarily histamine). Important in allergic diseases and host defense against parasites.
