Cell-mediated immunity to Epstein-Barr virus (EBV) and natural killer (NK)-cell activity in the X-linked lymphoproliferative syndrome.

The activity of T-cell-mediated immunity to Epstein-Barr virus (EBV) was assessed by an assay of regression of the outgrowth of EBV-infected autologous B cells. Regression and natural killer (NK)-cell activities were compared for patients and their mothers from five families with X-linked lymphoproliferative syndrome (XLP) and three control groups. Seven of the 10 patients with XLP exhibited weak T-cell activity against autologous EBV-infected lymphoblastoid cell lines (LCL) comparable to EBV-seronegative controls. In contrast, 8 of 10 obligate carrier females of XLP had unusually strong activity, which was comparable to anti-early-antigen (EA) positive controls. The results of the regression assays correlated with their EBV serology: mothers showed high titers, and their affected sons showed low-titer EBV-specific antibody responses. Defective NK-cell activity was found only in the patients with XLP. NK and regression activities did not correlate. Our findings explain, in part, the vulnerability to EBV of males with XLP and why their mothers are protected from life-threatening phenotypes of XLP.