Human natural cytotoxic cells: activation by a measles virus-induced lymphocyte factor which increases the expression of the HNC-1A3 antigen.

When human lymphocytes were exposed to measles virus antigen or to SSPE virus-infected cells, their cytotoxic activity against uninfected MA-160 cells was markedly enhanced. In contrast, mumps virus or herpes simplex virus-infected cells did not show such an enhancing effect and were rather inhibitory. SSPE cells and measles virus antigen, but not mumps-virus-infected cells or mumps virus antigen, also induced a two-fold increase in the number of lymphocytes bearing the HNC-1A3 membrane antigen, which we recently reported to be associated with a natural cytotoxic cell population. Pretreatment of SSPE cells or measles virus antigen with anti-measles antibody abolished the enhancing effect. Heat-treating the cells or the antigen at 56 degrees C for 30 min similarly abolished the effect. Supernatants of lymphocyte-SSPE cell cocultures were also effective in enhancing natural cytotoxicity. The soluble factor was a low molecular weight dialyzable molecule which was unaffected by boiling or trypsinization. It was released within 4 hours of coculture even in the presence of cycloheximide or following irradiation. Neither interferon nor leukotriene B4 appeared to be responsible for this enhancement. Virus-lymphocyte interaction may thus enhance natural cytotoxic cell activity through the rapid production or release of a virus-induced small molecular weight lymphocyte factor.