Generation of chemotactic factors by Rhizopus oryzae in the presence and absence of serum: relationship to hyphal damage mediated by human neutrophils and effects of hyperglycemia and ketoacidosis

Abstract

As our previous studies had shown that human neutrophils could kill Rhizopus oryzae hyphae in vitro, interactions of these hyphae with neutrophils and serum were further explored. Heated or fresh normal human sera suppressed hyphal metabolic activity as determined by [14C]uracil uptake, but severe ketoacidosis (8 X 10(-3) M beta-hydroxybutyric acid plus 2 X 10(-3) M acetoacetic acid at pH 7.0) negated this effect. Hyperglycemia (500 mg/dl) and severe ketoacidosis did not affect damage to hyphae by human neutrophils. Hyphae generated factors from sera which induced comparable chemotactic responses by neutrophils obtained from both normal and diabetic subjects, using a leading front assay performed in modified Boyden chambers. Zymosan-stimulated neutrophil chemotaxis was marginally depressed only by the combined elevation of both glucose (500 mg/dl) and ketoacids (10(-2)M) irrespective of pH (7.0 to 7.4), but not by any of these factors alone. Protein-containing supernatants from live or killed hyphae were chemotactic in the absence of serum based upon "checkerboard" assays varying the concentrations of hyphal supernatants above and below filters in the Boyden chambers. The supernatant-induced chemotactic response by neutrophils from diabetic subjects was minimally less than that of normal neutrophils (P less than 0.05). These findings indicate that R. oryzae hyphae can generate chemotactic factors which might prove to influence the inflammatory response to infections in vivo, and that severe hyperglycemia and ketoacidosis might affect interaction between the host and invading hyphae in mucormycosis.