The defensive role of interferon-γ-producing immature myeloid cells in severe invasive group A Streptococcus infections (118.7)

Abstract

Abstract Streptococcus pyogenes (group A Streptococcus; GAS) is one of the most versatile bacteria among human pathogens. Non-invasive GAS infections can cause common diseases, such as pharyngitis and impetigo. Whereas, severe invasive GAS infections can lead to rapid progressive and life-threatening manifestations, including sepsis, necrotizing fasciitis, and streptococcal toxic shock syndrome (STSS). Although GAS-derived superantigens activate T cells to release excessive amounts of cytokines which are considered to participate in the pathogenesis of STSS following severe invasive GAS infections, it remains unclear which factors are protective against such infections and which cell population is the source of them. Here we show that mice infected with severe invasive GAS isolates, but not with non-invasive GAS isolates, exhibit high concentrations of plasma interferon (IFN)-γ during the early stage of infection. IFN-γ is necessary to protect mice, and is produced by a novel population of granulocyte-macrophage colony-stimulating factor (GM-CSF)-dependent immature myeloid cells with ring-shaped nuclei (IFN-γ-producing immature myeloid cells; γIMCs). These γIMCs express monocyte and granulocyte markers, and also produce nitric oxide. The adoptive transfer of γIMCs ameliorates infection in wild-type and IFN-γ-deficient mice. Our results indicate that γIMCs have a defensive role during the early stage of severe invasive GAS infections.