Enhanced killing of Blastomyces dermatitidis by gamma interferon-activated murine peripheral blood polymorphonuclear neutrophils

Abstract

Normal peripheral blood polymorphonuclear neutrophils (PB-PMNs), challenged in vitro with yeast form Blastomyces dermatitidis, reduced inoculum colony-forming units of a virulent strain by 37.5 ± 9.5%. Pre-incubation of PB-PMNs with 10–100,000 U/ml of purified recombinant murine γ-interferon (IFN) for 1 h prior to challenge with fungi resulted in significant enhancement of PB-PMN fungicidal activity. No direct fungicidal activity by IFN alone was observed. Pretreatment of selected concentrations of IFN shown to have PMN-enhancing activity (100 or 1000 U/ml) with rabbit hyperimmune anti-IFN antiserum for 1 h before addition to PB-PMNs abrogated the enhancement of fungicidal activity. Isolated peripheral blood mononuclear cells failed to kill B. dermatitis, even when mononuclear cells were present at a concentration ten times greater than that normally used in killing assays, and failed to be activated by IFN. Treatment of unstimulated or IFN-activated PB-PMNs with complement and hybridoma-derived monoclonal antibody specific for PMNs eliminated PB-PMN fungicidal activity. Exogenously added lipopolysaccharide (0.0005 – 50,000 ng/ml) did not activate PB-PMNs, whether added alone or in conjunction with IFN. The PB-PMN activating capacity of IFN could be destroyed by heat treatment (100°C, 15 min) or by acid treatment with HCl (pH 2). These results demonstrate that recombinant γ-interferon can stimulate PB-PMNs to kill B. dermatitidis, that the PB-PMN activating moiety is IFN and that PB-PMNs are responsible for fungal killing in this assay system. These results suggest that PB-PMNs may play an important role in host defense againts B. dermatitidis and that in vivo activation of PB-PMNs by IFN may augment this defense. IFN may also represent a therapeutic approach to fungal diseases.