The capacity of human peripheral blood monocytes, neutrophils, and monocyte-derived macrophages to bind the yeast Cryptococcus neoformans was increased when the phagocytes were cultured on surfaces containing recombinant human mannose-binding protein. In contrast, soluble mannose-binding protein had no effect on cryptococcal binding by phagocytes.

The lymphokine interleukin-2 (IL-2), which is necessary for the generation of an optimal cell-mediated immune response, has recently been shown to have lectinlike properties, with specificity for high-mannose groups. Therefore, the ability of IL-2 to bind to the mannose-rich fungus Candida albicans was examined. Heat-killed fungi preincubated with IL-2 stimulated, in a dose-dependent manner, proliferation of the IL-2-dependent cell line CTLL20. Soluble mannan, which is rich in exposed mannose groups, inhibited binding of IL-2 to C. albicans by approximately 60%, suggesting that the lectinlike properties of IL-2 are partially responsible for its fungal binding capacity. Binding of IL-2 to fungi appeared to be reversible, as C. albicans preincubated with IL-2 stimulated CTLL20 proliferation even when the fungi and cells were separated by an 0.4-,um-pore-size membrane. The lymphoproliferative response of normal human peripheral blood mononuclear cells to C. albicans was augmented when the fungus was preincubated with IL-2. Binding of 1251-IL-2 could not be inhibited by unlabeled IL-2, suggesting the absence of high-affinity receptors on C. albicans for IL-2. While the in vivo relevance remains to be determined, these data demonstrate that IL-2 can bind to C. albicans in vitro and thereby influence the host response to this medically important fungus.

No abstract