Humoral Immune Response
. The humoral immune response involves a complex series of events after antigens enter the body. First, macrophages take up some of the antigen and attach it to class II MHC molecules, which then present the antigen to T helper cells. The T helper cells bind the presented antigen, which stimulates the T helper cells to divide and secrete stimulatory molecules called interleukins. The interleukins in turn activate any B lymphocytes that have also bound the antigen. The activated B cells then divide and secrete antibodies. Finally, the secreted antibodies bind the antigen and help destroy it. Antibodies Antibodies are Y-shaped proteins called immunoglobulins (Ig) and are made only by B cells. The antibody binds to the antigen at the ends of the arms of the Y. The area at the base of the Y determines how the antibody will destroy the antigen. This area is used to categorize antibodies into five main classes: IgM, IgG, IgA, IgD, and IgE. During the humoral immune response, IgM is the first