DIRECT ACTIVITY OF HUMAN T-LYMPHOCYTES AND NATURAL-KILLER-CELLS AGAINST CRYPTOCOCCUS-NEOFORMANS

Lymphocytes constitute a critical component of host defenses against c ryptococcosis, Previously, we demonstrated that human lymphocytes cult ured with interleukin-2 formed conjugates with, and directly inhibited the growth of, Cryptococcus neoformans. Here, we explore the anticryp tococcal activity of freshly isolated, highly purified populations of human peripheral blood lymphocytes. Lymphocytes were incubated with en capsulated C. neoformans for 24 h, after which the lymphocytes were ly sed, dilutions and spread plates were made, and CFU were counted. Fung istasis was determined by comparing growth in wells with and without l ymphocytes. Nylon wool-nonadherent peripheral blood mononuclear cells (NWNA PBMC) were highly fungistatic, even if either T cells or natural killer (NK) cells were depleted by panning. A mixed population of T c ells and NK cells, obtained by resetting NWNA PBMC with sheep erythroc ytes, completely inhibited cryptococcal growth, whereas the nonrosetti ng cells had little fungistatic activity. CD4(+), CD8(+), and CD16/56( +) lymphocytes, isolated by positive immunoselection, had potent growt h-inhibitory activity. In contrast, purified B cells had no activity. Fungistasis was seen even in the absence of opsonins. Antifungal activ ity was markedly diminished when surface receptors on NWNA PBMC were c leaved by treatment with trypsin or bromelain, Supernatants from stimu lated lymphocytes or concentrated lymphocyte sonicates were not active . Lymphocyte-mediated fungistasis was seen with two different strains of C. neoformans. CD4(+), CD8(+), and CD16/56(+) lymphocytes formed co njugates with C. neoformans, as observed under Nomarski differential i nterference contrast microscopy and videomicroscopy. These data demons trate that freshly isolated peripheral blood T cells and NK cells have the capacity to bind and directly inhibit the growth of C. neoformans .