How does gamma-interferon mediate resistance to Listeria monocytogenes?

Gamma-interferon (IFN-gamma) seems to be required for resistance to Listeria monocytogenes in vivo, but acts early in infection, before apparent T cell involvement. The early role of IFN-gamma is unknown, but might include enhancing antigen presentation, inducing secretion of tumor necrosis factor alpha and helping early precursor macrophages to express nonspecific listericidal activity.