Candida, the most common causes of opportunistic mycoses, are increasingly important complications of transplantation, antitumor therapy, and AIDS. Neutrophils (PMN), the critical determinants of resistance to dissemination of candidiasis, can attach to and then kill opsonized or unopsonized C. albicans hyphae by a process requiring oxidant generation. Recombinant human interferon-gamma (IFN), tumor necrosis factor-alpha (TNFalpha), and a granulocyte-macrophage colony stimulating factor (GM-CSF), 3 cytokines known to enhance PMN responses, all increase hyphal-stimulated release of direct respiratory burst products but both IFN and GM-CSF augment fungicidal activity, while TNFalpha reduces it and fosters less HOC1 release, a product formed by combined respiratory burst and degranulation responses. Optimum killing efficiency requires coordinated and modulated release of oxidants and granule constituents to maximize antimicrobial cytotoxicity while minimizing adverse inflammatory effects on host cells. Since the respiratory burst and degranulation are separately regulated responses, factors controlling their coordination must be better defined. In unprimed PMN, opsonized or unopsonized hyphae and other stimuli elicit strikingly different patterns of early biochemical events, making them invaluable probes for defining signal transduction pathways. Likewise, specific opsonins are critical determinants of PMN responses, since triggering via various surface receptors elicits different specific events. A remarkable heterogeneity of responses to hyphae also is likely to affect microbicidal activity by individual PMN. Cytokines also have unique effects on PMN activation responses, some correlating with increased RNA transcription. To define molecular mechanisms for the differing effects of IFN, TNFalpha, and GM-CSF on PMN fungicidal activity, we will determine and compare changes induced by each cytokine on hypal attachment and killing responses; define receptor-specific response patterns using selectively opsonized hyphae and antireceptor monoclonal antibodies; then correlate these findings with specific patterns of activation of biochemical events (ion fluxes, patterns of activation of guanine nucleotide regulatory proteins, membrane lipid metabolism, dependence on phosphorylation mediated by protein kinase C, cytoskeleton responses, antioxidant control mechanisms) defined in individual PMN and whole PMN populations. Dependence and independence of cytokine responses on RNA and protein synthesis will be identified, and changes in RNA transcription responsible for specific, cytokine-mediated effects on the events that determine efficacy of PMN mechanisms then defined.
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