Antibody-Mediated Immunity
An antigen is present within body fluids, when a phagocyte engulfs the antigen and presents it on an MHC II molecule as an APC. A T helper cell recognizes and correctly fits with the MHC II complex. This stimulates clonal selection of B cells, B memory cells and plasma cells. Plasma cells are the effector cells of a B cell clone; they secrete antibodies, which in turn circulate in the lymph and blood to reach the site of invasion. They secrete hundreds of millions of antibodies each day for about 4 to 5 days until the plasma cell dies.
Antibodies
An antibody can combine specifically with the epitope on the antigen that triggered its production. The antibody’s structure matches its antigen like a lock and key. Antibodies are known as immunoglobulins (Igs). Igs have an Antigen-Binding Site. This is the part that recognizes and attaches specifically to a particular antigen. There are five different classes of Igs: IgG, IgA, IgM, IgD, IgE each with a distinct structure and a specific role in the body.
Antibody Action
Neutralization – Ab neutralizes antigen Immobilization – Ab decreases the mobility of the antigen Agglutination – Ab and antigen clump together Precipitation – Ab and antigen complex falls out of solution Phagocytosis – Ab and antigen complex is phagocytized
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