Unopsonized Candida albicans hyphae stimulate a neutrophil respiratory burst and a cytosolic calcium flux without membrane depolarization.

We have defined major differences between events elicited during activation of human neutrophils by opsonized Candida hyphae (noningestible) or zymosan (ingestible) and by unopsonized Candida hyphae (also noningestible). In response to opsonized particles, a transient increase in cytosolic free calcium was initially observed, followed by depolarization in the transmembrane potential and a respiratory burst. Without opsonins, zymosan did not elicit a response from neutrophils. In contrast, unopsonized Candida hyphae elicited a transient increase in cytosolic calcium, as well as triggered a respiratory burst; they did not, however, elicit a depolarization of the neutrophil membrane. Furthermore, the rate of superoxide generation decreased after a prolonged lag period. The calcium flux was also delayed and coincided with the onset of superoxide generation. Thus, our data demonstrate that Candida albicans hyphae activate neutrophils in the absence of added serum components and initiate a neutrophil respiratory burst without an antecedent membrane depolarization.