immunodeficiency disease /-difish″ənsē/ , any of a group of diseases caused by a defect in the immune system and generally characterized by susceptibility to infections and chronic diseases. Such diseases are sometimes classified as B cell (antibody) deficiencies, T cell (cellular) deficiencies, combined T and B cell deficiencies, defects of cell movement, and defects of microbicidal activity. See also severe combined immunodeficiency disease.
