An antibody is a protein produced by a host to bind to foreign particles and inactivate them. Ideally, the antibody binds to only their specific antigen. Antigens are defined as anything that makes the immune system respond by producing antibodies. They are often viruses, bacteria, or fungi, but can sometimes be dust, chemicals, pollen, or food proteins that cause allergic reactions. (Antigens that cause allergic reactions are called allergens). An epitope is the part of the antigen to which the antibody binds.

Once the immune system has created and antibody for an antigen whose attack it has survived, it continues to produce antibodies for subsequent attacks from that antigen. The long term memory of the immune system is the basis for vaccinations against disease. The immune system has the ability to recognize, remember, and destroy over a million different antigens. T cells vs. B cells In the embryo, T lymphocytes are produced in the bone marrow and thymus. They then migrate to the spleen, lymph nodes, and lymph nodules. B lymphocytes are produced in the embryonic bone marrow and migrate to the spleen and lymph nodes and nodules as well.

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T and B cell immunity is specific, meaning that one foreign antigen is the target each time a mechanism is activated. Both T and B cells are capable of recognizing foreign antigens. Foreign antigens are phagocytized by a macrophage and parts of it are presented on the macrophage’s cell membrane, along with the macrophage’s self antigens. Helper T cells encounter the macrophage and see both the self and foreign antigens for comparison. This causes the helper T cells to become sensitized to and specific for the foreign antigen.

Memory T cells remember the specific foreign antigen and become active if it enters the body again. Cytotoxic T cells are able to chemically destroy foreign antigens by disrupting cell membranes. They also produce cytokines, which attract macrophages to the area and activate them to phagocytize the foreign antigen. Antibody-mediated immunity happens when a foreign antigen is recognized by macrophages, helper T cells, and B cells. The helper T cell presents the foreign antigen to B cells and the B cells manufacture the antibodies to fight off the antigens.