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1. The production by B lymphocytes of specific antibodies and by T lymphocytes of specific cellular reactions to a foreign antigen. When the antigen is encountered again, an immune response occurs. The production of antibodies by B lymphocytes or the activation of T lymphocytes when an allergen is first encountered. When the allergen is encountered again, an abnormal immune response occurs.
SEE: hypersensitivity.
2. The process of making a person susceptible to a substance by repeated injections of it.
SYN: SEE: sensibilization.

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