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Unformatted text preview: antigens might be bacteria, viruses, protozoa, fungi or helminths. Substances include pollen, insect venom, and transplanted tissue. Body cells that change and become cancerous may also be perceived as foreign and act as antigens, so cancers may be eliminated in very early stages by our immune system. HUMORAL (ANTIBODY-MEDIATED) IMMUNITY This involves the production of antibodies, which are found in extracellular fluids such as blood plasma, lymph, and mucus secretions. Antibodies are produced by B lymphocytes (B cells) which have changed in response to the presence of foreign material and become plasma cells. This type of defense works best against: Most bacteria Bacterial toxins Viruses that have not yet invaded cells Part of the response against transplanted tissue...
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- Fall '09