1113Your immune system is responsible for helping to eliminate any unwanted invaders, or antigens, such as infectious organisms. The key cells in your immune system are lymphocytes known as B cells and T cells, which originate in the bone marrow. After T cells further develop in the thymus, all the immune cells gather in lymph nodes and the spleen. Antigens are ingested (1), partially digested (2), and then presented to helper T cells (3) by special cells called macrophages. This process activates the helper T cell to release hormones (lymphokines) (4) that help B cells develop. These hormones along with recognition of further antigens (5) change the B cell (6) into an antibody-producing plasma cell. The antibodies produced (7) can be one of several types (IgG, IgM, IgA, and IgE). The antibody "fits" the antigen much like a key fits a lock. The antigen is thus rendered harmless. Helper T cells also aid in development (8) of cytotoxic T cells, which can kill antigens directly. Memory T cells are produced (9) so that re-exposure to the same antigen (10) will provide a more rapid and effective response.
