Primary and secondary abnormalities of T cell subpopulations.

Ataxia telangiectasia patients had normal numbers of T lymphocytes in their blood but IgM-binding T lymphocytes (T(M)) were selectively reduced. These changes provide a cellular basis for the defects in cell-mediated immunity which occur in this primary condition. One child with severe combined immunodeficiency lacked both T(M) and IgG-binding (T(G)) T lymphocytes, but no consistent abnormalities of T cell subsets were found in other primary immunodeficiency syndromes. Secondary increases in IgG-binding T lymphocytes (T(G)) were found in children receiving steroids.