title: Independence of neutrophil respiratory burst oxidant generation from the early cytosolic calcium response after stimulation with unopsonized Candida albicans hyphae.
abstract: We previously noted differences between neutrophil responses to unopsonized Candida albicans hyphae and responses to other particulate stimuli such as opsonized hyphae or zymosan; these differences include delayed rises in cytosolic calcium [( Ca2+]i), 1,4,5-inositol trisphosphate, and superoxide release and the total absence of early membrane depolarization. Respiratory burst stimulation is required for killing of C. albicans hyphae. Since an early rise in [Ca2+]i may act as a second messenger for burst activation by most agonists, we chelated (Ca2+)i and extracellular Ca2+ [( Ca2+)e] to compare requirements for superoxide responses to hyphae and other stimuli. Intracellular chelation, which ablated early [Ca2+]i rises, eliminated the fMet-Leu-Phe-induced respiratory burst and profoundly reduced that response to opsonized zymosan (by 96.7%), but chelation of both (Ca2+)i and (Ca2+)e only partially inhibited responses to opsonized and unopsonized hyphae (60.5 and 23.3%, respectively; the latter exceeded absolute responses evoked by opsonized zymosan, a 12-fold-more-potent stimulus for unchelated cells). Simultaneous (Ca2+)i and (Ca2+)e chelation further decreased superoxide responses to opsonized zymosan and hyphae (99.4 and 90.4%, respectively) but not to unopsonized hyphae (26.7% inhibition). Though both ingestible (zymosan) and uningestible (hyphae) opsonized particulate stimuli elicited reduced but significant respiratory bursts without early [Ca2+]i rises, the greater superoxide responses and sensitivity to chelation with opsonized zymosan suggest important differences in initiation and/or regulation of responses to these particulate stimuli. In contrast, the respiratory burst elicited by unopsonized hyphae appeared largely Ca2+ independent. If different events mediate neutrophil activation by opsonized and unopsonized hyphae, candidacidal activity in vivo may vary under divergent conditions with specific localized sites of infection.
authors.affiliation: Evans Memorial Department of Clinical Research, University Hospital, Boston University Medical Center, Massachusetts 02118.
authors.forename: D R
authors.initials: DR
authors.lastname: Wysong
authors.forename: C A
authors.initials: CA
authors.lastname: Lyman
authors.forename: R D
authors.initials: RD
authors.lastname: Diamond
mesh_terms: D002118:Calcium / Q000502:physiology*; D002176:Candida albicans / Q000276:immunology*; D003600:Cytosol / Q000502:physiology; D004533:Egtazic Acid / Q000494:pharmacology / Q000031:analogs & derivatives; D006801:Humans; D066298:In Vitro Techniques; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils / Q000502:physiology*; D010587:Phagocytosis; D013481:Superoxides / Q000378:metabolism*; D015054:Zymosan / Q000494:pharmacology
chemical_list: D013481:Superoxides; D004533:Egtazic Acid; D009240:N-Formylmethionine Leucyl-Phenylalanine; D015054:Zymosan; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium