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A fragment (also known as C3a) of complement C3 that causes cellular release of histamine.


An immunoglobulin protein produced by the immune system, designed to bind to a specific single antigen. Antibodies neutralize foreign antigens; form immune complexes; activate complement; sensitize target cells, mast cells, and basophils; and initiate opsonization.


Any substance (or molecule) capable of inducing a specific immune response. Antigens include a wide variety of plant and microorganism components or toxins.


An acute-phase reactant plasma glycoprotein.

Arthus reactions.

Dermal skin test reactions (characteristic of Type III hypersensitivities), that occur during a 4–12 h interval.

Autoimmune disease.

Any disease caused by the immune system's erroneous and destructive actions on the body's own tissues, such as thyroiditis, myocarditis, glomerulonephritis, and lupus erythematosus.



A white blood cell (WBC) with granules that can be stained by basic dyes. Basophils participate in inflammatory processes and in allergic and hypersensitivity reactions by releasing histamine.

B-cells (or B-lymphocytes).

Thymus-independent, bursa-equivalent lymphocytes produced by bone marrow to populate all lymphoid organs and tissues. They are capable of producing antibodies and maturing into plasma cells. B-cells express antibody on their surfaces that can respond to foreign protein, polysaccharide, and lipid antigens in soluble form.



A proteinase enzyme released by polymorphonuclear leukocytes during inflammation.

Cell-mediated immunity.

Antigen-specific and nonspecific immunity provided by the direct localized cellular activity of T-lymphocytes and natural killer cells. Specific cells include T–helper cells (Th) and T–cytotoxic cells (Tc); nonspecific cells include macrophages, neutrophils, eosinophils, and NK-cells.

CD4+ cells.

Helper T-cells recognized by the presence of cluster of differentiation antigen 4 on their exterior cell surfaces.

CD8+ cells.

Suppressor T-cells recognized by the presence of cluster of differentiation antigen 8 on their exterior cell surfaces.

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