Direct activity of human T lymphocytes and natural killer cells against Cryptococcus neoformans

Abstract

Lymphocytes constitute a critical component of host defenses against cryptococcosis. Previously, we demonstrated that human lymphocytes cultured with interleukin-2 formed conjugates with, and directly inhibited the growth of, Cryptococcus neoformans. Here, we explore the anticryptococcal activity of freshly isolated, highly purified populations of human peripheral blood lymphocytes. Lymphocytes were incubated with encapsulated C. neoformans for 24 h, after which the lymphocytes were lysed, dilutions and spread plates were made, and CFU were counted. Fungistasis was determined by comparing growth in wells with and without lymphocytes. 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 cells and NK cells, obtained by rosetting NWNA PBMC with sheep erythrocytes, completely inhibited cryptococcal growth, whereas the nonrosetting cells had little fungistatic activity. CD4+, CD8+, and CD16/56+ lymphocytes, isolated by positive immunoselection, had potent growth-inhibitory activity. In contrast, purified B cells had no activity. Fungistasis was seen even in the absence of opsonins. Antifungal activity was markedly diminished when surface receptors on NWNA PBMC were cleaved by treatment with trypsin or bromelain. Supernatants from stimulated 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 conjugates with C. neoformans, as observed under Nomarski differential interference contrast microscopy and videomicroscopy. These data demonstrate that freshly isolated peripheral blood T cells and NK cells have the capacity to bind and directly inhibit the growth of C. neoformans.

The Regulation of Pulmonary Immunity

“…Recent studies indicated that human NK cells and T cells had direct activity in vitro against Cne (Levitz et al, 1994;Murphy et al, 1993), although there was conflicting evidence that human NK cells had no growth-inhibiting activity unless antibody against the organism was present (Miller et al, 1990). We demonstrated that murine NK cells had a minor effect against the organism following iv inoculation, but failed to play a role in early lung clearance if the organism was inoculated via the trachea .…”

The immune response to fungal infections

“…T cells and NK cells have direct anti-cryptococcal activity. In vitro, CD4 + and CD8 + T lymphocytes directly inhibit fungal growth by attaching to the cryptococcal cell surface (Murphy et al, 1993;Levitz et al, 1994). Binding of NK cells to the fungus and release of cytolytic compounds leads to direct killing.…”

Cryptococcus neoformans infection in mice previously infected with LP-BM5 MuLV, the agent of murine AIDS (MAIDS)

“…Experimental studies have shown that CD4 T lymphocyte depletion leads to the dissemination of C. n e o f o m n s from the lungs [22], and CD8 T cell depletion impairs clearance of both avirulent and virulent strains from the lungs [3,4]. CD4 and CD8 T cells also have a fungistatic activity, by direct contact with cryptococci [23]. In our study, the failure of MAIDS-induced immunosuppression to affect the control of C. neoformans could be related to the lack of decrease in CD4+ and CD8+ cells in blood (data not shown) and spleen ( Table 3).…”