Inhibition of neutrophil killing of Candida albicans pseudohyphae by substances which quench hypochlorous acid and chloramines.

Using a microtiter plate killing assay, we investigated the in vitro killing of Candida albicans by human neutrophils and by hypochlorous acid/hypochlorite ion (HOCl/OCl-) or chloramine solutions to evaluate the inhibition of this process by quenchers of these oxidants. Methionine, tryptophan, and alanine were able to effectively inhibit neutrophil killing of candida pseudohyphae. These substances were capable of quenching the oxidant activity of NaOCl, monochloramine (NH2Cl), and to a lesser extent, taurine chloramine. NaOCl and NH2Cl were able to kill C. albicans in the absence of inhibitors in concentrations of less than 5 microns M, whereas greater than 100 microns M taurine chloramine was required for killing. Methionine and tryptophan were capable of markedly inhibiting killing by all three oxidants, whereas alanine affected only killing by NaOCl. The oxidant activity of NaOCl was more readily quenched by opsonized or unopsonized Candida yeast than was the oxidant activity of either NH2Cl or taurine chloramine. These results suggest that some substances which quench the oxidizing activity of the products of the neutrophil myeloperoxidase system can inhibit the killing of C. albicans by these cells.