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| any disease-producing agent, especially a virus, bacterium, or other microorganism. |
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| A disease resulting from the presence and activity of a pathogenic microbial agent. |
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| a heterocyclic amine, C 5 H 9 N 3 , released by mast cells when tissue is injured or in allergic and inflammatory reactions, causing dilation of small blood vessels and smooth muscle contraction. |
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| any of various proteins, produced by virus-infected cells, that inhibit reproduction of the invading virus and induce resistance to further infection. |
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| the state of being immune from or insusceptible to a particular disease or the like. |
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| any substance that can stimulate the production of antibodies and combine specifically with them. |
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| any of numerous Y -shaped protein molecules produced by B cells as a primary immune defense, each molecule and its clones having a unique binding site that can combine with the complementary site of a foreign antigen, as on a virus or bacterium, thereby disabling the antigen and signaling other immune defenses. |
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| a type of lymphocyte, developed in bone marrow, that circulates in the blood and lymph and, upon encountering a particular foreign antigen, differentiates into a clone of plasma cells that secrete a specific antibody and a clone of memory cells that make the antibody on subsequent encounters. |
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| any of several closely related lymphocytes, developed in the thymus, that circulate in the blood and lymph and orchestrate the immune system's response to infected or malignant cells, either by lymphokine secretions or by direct contact: helper T cells recognize foreign antigen on the surfaces of other cells, then they stimulate B cells to produce antibody and signal killer T cells to destroy the antigen-displaying cells; subsequently suppressor T cells return the immune system to normal by inactivating the B cells and killer T cells. |
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| an antibody-secreting cell, derived from B cells, that plays a major role in antibody-mediated immunity. |
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| acquired immunity in which the role of circulating antibodies is predominant. |
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| immunity independent of antibody but dependent on the recognition of antigen by T cells and their subsequent destruction of cells bearing the antigen or on the secretion by T cells of lymphokines that enhance the ability of phagocytes to eliminate the antigen. |
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| a T cell that stimulates B cells to produce antibody against a foreign substance, using lymphokines or direct contact as a signal. |
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| any small, long-lived lymphocyte that has previously encountered a given antigen and that on reexposure to the same antigen rapidly initiates the immune response (memory T cell) or proliferates and produces large amounts of specific antibody (memory B cell) the agent of lasting immunity. |
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| any preparation used as a preventive inoculation to confer immunity against a specific disease, usually employing an innocuous form of the disease agent, as killed or weakened bacteria or viruses, to stimulate antibody production. |
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| immunity in an organism resulting from its own production of antibody or lymphocytes. |
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| immunity in an organism resulting from its own production of antibody or lymphocytes. |
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| an abnormal reaction of the body to a previously encountered allergen introduced by inhalation, ingestion, injection, or skin contact, often manifested by itchy eyes, runny nose, wheezing, skin rash, or diarrhea. |
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| a disease resulting from a disordered immune reaction in which antibodies are produced against one's own tissues, as systemic lupus erythematosus or rheumatoid arthritis. |
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| a disease of the immune system characterized by increased susceptibility to opportunistic infections, as pneumocystis carinii pneumonia and candidiasis, to certain cancers, as Kaposi's sarcoma, and to neurological disorders: caused by a retrovirus and transmitted chiefly through blood or blood products that enter the body's bloodstream, especially by sexual contact or contaminated hypodermic needles. |
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| Human immunodeficiency virus, a retrovirus that causes AIDS. |
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