Monoclonal proliferation of CD4+ large granular lymphocytes with cytolytic activity

Summary. A rare case of monoclonal proliferation of CD3⁺4⁺8～ T-cell receptor-αβ⁺ large granular lymphocytes (LGL) is presented. CD4⁺ LGL in the present case showed spontaneous cytotoxicity against herpes simplex virus-infected cells and antibody- and lectin-dependent cytotoxicity. Perforin, which is one of the important cytolytic mediators of cytotoxic T cells (CTL) and natural killer cells, was abundantly expressed in CD4⁺ LGL of this case. The present case suggests that perforin-positive CD4⁺ CTL, which have recently been shown in the in vitro studies, certainly exist in vivo.