Gamma interferon induces monocyte killing of Listeria monocytogenes by an oxygen-dependent pathway; alpha- or beta-interferons by oxygen-independent pathways.

Human peripheral blood monocytes purified by counterflow centrifugal elutriation were treated with recombinant interferons-gamma (IFN-gamma), alpha (IFN-alpha), or beta (IFN-beta)--and tested for their capacity to kill Listeria monocytogenes. All three IFNs increased the monocyte bactericidal activity in a dose-dependent fashion. Exogeneous catalase, an inhibitor of monocyte-generated hydrogen peroxide, did not affect bactericidal activity. However, exogenous superoxide dismutase inhibited killing by IFN-gamma-activated monocytes, but not by IFN-alpha- or IFN-beta-activated monocytes. By contrast, exogenous soybean trypsin inhibitor inhibited killing by IFN-alpha or IFN-beta-activated monocytes, but not by IFN-gamma-activated monocytes. Combinations of IFN-gamma and IFN-alpha resulted in no increase in bactericidal activity. Finally, treatment with IFN-gamma resulted in different receptiveness of the cell to subsequent oxidative burst-stimulating signals than did treatment with either IFN-alpha or IFN-beta. These results suggest that monocytes treated with IFN-gamma kill L. monocytogenes by an oxygen-dependent mechanism, but treatment with IFN-alpha or IFN-beta elicits principally oxygen-independent mechanisms.