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 (TM) 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 TM and IgG-binding (TG) T lymphocytes, but no consistent abnormalities of T cell subsets were found in other primary immunodeficiency syndromes. Secondary increases in IgG-binding T lymphocytes (TG) were found in children receiving steroids.