Aberrant humoral responses

Self-directed humoral immunity

Immunological tolerance is the process that normally prevents lymphocytes from reacting with self antigens. Under certain circumstances, immunological tolerance breaks down and autoimmune disease results. Humoral antibodies to self antigens on cell surfaces can lead to cell death by direct complement-mediated cell lysis, by ADCC or by opsonization. Antibodies directed against hormones or against cell surface receptors may interfere with cell function. One such example is the autoimmune disease myasthenia gravis, where antibodies react with the receptor for acetylcholine at the neuromuscular junction.

In addition in autoimmune diseases such as systemic lupus erythematosus, the continued production of autoantibody to self antigens leads to the formation of large amounts of immune complexes which are deposited in various tissues. These complexes activate the complement cascade, which leads to acute local inflammation at the site of deposition. Various serious diseases such as vasculitis, nephritis, endocarditis or rheumatoid arthritis may be the result.

Immediate-type hypersensitivity reaction

The immediate-type reaction, in contrast to delayed-type hypersensitivity, is always a humoral immune response. In an organism sensitized by a given allergen, a new contact with the allergen will lead to an immediate reaction. The localization of the allergen by specific antibodies of the IgE class (reagin) on to mast cells leads to the activation of the mast cells. The resulting degranulation of the mast cells releases mediators such as histamine, serotonin, heparin and proteolytic enzymes. The result is an immediate inflammation reaction which may range from a local skin reaction to a potentially lethal anaphylactic shock.

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