Early IL-10 promotes vasculature-associated CD4+ T cells unable to control Mycobacterium tuberculosis infection.

Cytokine-producing CD4+ T cells play a crucial role in the control of Mycobacterium tuberculosis (Mtb) infection; however, there is a delayed appearance of effector T cells in the lungs following aerosol infection. The immunomodulatory cytokine IL-10 antagonizes control of Mtb infection through mechanisms associated with reduced CD4+ T cell responses. Here, we show that IL-10 overexpression only before the onset of the T cell response impairs control of Mtb growth. During chronic infection, IL-10 overexpression reduces the CD4+ T cell response without impacting the outcome of infection. IL-10 overexpression early during infection did not significantly impair the kinetics of CD4+ T cell priming and effector differentiation; however, CD4+ T cells primed and differentiated in a IL-10-enriched environment display reduced expression of CXCR3 and do not migrate into the lung parenchyma thereby limiting their ability to control infection. Importantly, these CD4+ T cells maintain their vasculature phenotype and are unable to control infection even after adoptively transferred into low IL-10 settings. Together our data support a model wherein, during Mtb infection, IL-10 acts intrinsically on T cells impairing their parenchymal migratory capacity and ability to engage with infected phagocytic cells thereby impeding control of infection.