Impaired IMMUNITY resulting from inherited or acquired abnormalities of the immune system. This leads to increased vulnerability to infection. Important inherited examples of immunodeﬁciency are defects in function of GRANULOCYTES and the COMPLEMENT SYSTEM. Common acquired forms of immunodeﬁciency are defective function of B-type lymphocytes and hence antibody deﬁciency in ‘common variable hypogammaglobulinaemia’, and grossly deﬁcient CD4 T-cell function – malfunctioning T-type lymphocytes – in AIDS, secondary to HIV infection (see AIDS/HIV).
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