Direct anticryptococcal activity of lymphocytes from Cryptococcus neoformans-immunized mice

Assessment of the direct anticryptococcal activity of murine lymphocytes from both Cryptococcus neoformans-immunized and control mice was the focus of this investigation. We demonstrate that at a 2:1 effector cell-to-cryptococcal target cell ratio, effector cell populations comprised of alpha beta T-cell receptor-positive T lymphocytes (98 to 99% CD3+) from C. neoformans-immunized mice inhibited the growth of cryptococcal cells better than similar populations of lymphocytes from nonimmunized control mice. Almost immediately after mixing of cryptococci with the effector cells, C. neoformans-lymphocyte conjugates were observed. The percentage of conjugates increased over the first 30 min of incubation and then remained constant over the next 1.5 h. T-lymphocyte-enriched populations from C. neoformans-immunized mice formed significantly greater percentages of conjugates with cryptococci than control T lymphocytes at each time period that assessment was made. For growth inhibition to occur, direct contact between the effector and target cells was necessary, as evidenced by abrogation of cryptococcal growth inhibition when lymphocyte and cryptococcal cell populations were separated by a porous membrane during the growth inhibition assay. Vital staining of cryptococci after incubation with the T-cell-enriched populations showed that the T lymphocytes killed the cryptococcal cells.