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a deficiency of immune response or a disorder characterized by deficient immune response; classified as antibody (B cell), cellular (T cell), or combined deficiency disorders. Antibody immunodeficiencies are marked by hypo- or dysgammaglobulinemia, recurrent bacterial otitis media, and sinopulmonary infections. Cellular immunodeficiencies are characterized by recurrent low-grade or opportunistic infections, by graft-versus-host disease or reaction after blood transfusions, and by severe disease after immunization with live vaccines. See also acquired immunodeficiency syndrome.
common variable immunodeficiency (CVID) a heterogeneous group of disorders characterized by hypogammaglobulinemia, decreased antibody production in response to antigenic challenge, and recurrent pyogenic infections, often associated with hematologic and autoimmune disorders. Most patients have normal numbers of circulating B cells but lack plasma cells and appear to have an intrinsic defect of B cell differentiation. However, two other forms are also recognized: that due to a disorder of T lymphocyte regulation and that due to production of autoantibodies against T and B lymphocytes.
severe combined immunodeficiency (SCID) any of several rare congenital diseases, some of autosomal recessive and some of X-linked inheritance, in which both humoral and cell-mediated immunity fail to develop normally and T lymphocytes are absent or nearly so. In some forms, B lymphocytes are also absent. Early diagnosis is essential to prevent opportunistic infections. Persistent diarrhea, chronic mucocutaneous candidiasis, and failure to thrive may occur in infancy. Blood transfusions can result in graft-versus-host disease and routine vaccinations in fatal infection. Unless immune function is restored by a matched-donor bone marrow or fetal tissue transplantation or the patient is kept in complete isolation, the prognosis is poor.