Impaired autologous mixed lymphocyte reaction (AMLR) in patients with ataxia-telangiectasia and their family members.

We used the autologous mixed lymphocyte reaction (AMLR) to test T cell function in four patients with Ataxia-telangiectasia (AT), in 11 first-degree relatives and in 20 controls. There was a marked reduction of AMLR in the patients and in three relatives compared to the age-matched controls. In the AT patients the defect in AMLR was intrinsic to the CD4 subpopulation, since exogenous IL-2 did not improve the response of isolated CD4 cells. In contrast to normal controls, pre-incubation of autologous B cells with Epstein-Barr virus (EBV) did not enhance the reduced AMLR in the AT patients and the three first-degree relatives. We conclude that in both patients with AT and in some of their family members there is an intrinsic defect in CD4 T cells. This defect leads to diminished reactivity to EBV infected autologous B cells, and may explain in part the high incidence of malignancies observed in such families.