Macrophage-T cell interactions promote SLAMF1 expression for enhanced TB defense.

CD4+ T cells are crucial for protective immunity to intracellular pathogens. In addition to secreting cytokines, CD4+ T cells promote control of Mycobacterium tuberculosis infection through cognate interactions with macrophages, but the mechanism has been unclear. Here, we show that SLAMF1/CD150 is highly and uniquely induced in macrophages by antigen-specific interactions with CD4+ T cells. In macrophages, SLAMF1 enhances the generation of reactive oxygen species and restricts Mtb replication. Mtb-infection of mice promotes SLAMF1 expression specifically on infected macrophages, not uninfected bystanders. SLAMF1 expression depends on adaptive immunity and also autophagy. Moreover, Slamf1-/- mice have higher Mtb burden and more rapid disease progression than wild type mice. Using Slamf1fl/fl conditional knock-out mice, we show that in vivo Slamf1 is specifically required in macrophages to restrict mycobacterial growth and limit IL-1β production. In macaques, macrophage SLAMFI expression also correlates with T cell responses and protection. Combined, these data demonstrate that SLAMF1 is a marker of macrophage-T cells interactions, and it promotes protection against Mtb.