Phenotypic and functional T cell subset abnormalities in patients with aplastic anaemia and hypogammaglobulinaemia.

We have investigated T cell abnormalities present in blood of two patients with aplastic anaemia and hypogammaglobulinaemia. There was a marked increase in class II, major histocompatibility complex, HLA-DR+ antigen, and interleukin-2 receptor (Tac+) bearing CD4+ helper/inducer T cells, and a concurrent reduction of CD8+ suppressor/cytotoxic T cells. These CD4+ T cells produced an elevated proliferative response to phytohaemagglutinin and concanavalin A. Interestingly, the T cell subset mainly responsible for elevated production of the lymphokine, interleukin-2, under the stimulus of phytohaemagglutinin, was characterized as belonging to a CD4+ T cell subset. Functional studies, using a pokeweed mitogen driven IgG, IgA and IgM synthesis, demonstrated a correlation between CD4+ T cell deficient helper function for B cell differentiation and the clinical finding of the patient's hypogammaglobulinaemia.