Defective positioning in granulomas but not lung-homing limits CD4 T-cell interactions with Mycobacterium tuberculosis-infected macrophages in rhesus macaques

Protection against Mycobacterium tuberculosis (Mtb) infection requires CD4 Tcells to migrate into the lung and interact with infected macrophages. In mice, less-differentiated CXCR3(+) CD4 Tcells migrate into the lung and suppress growth of Mtb, whereas CX3CR1(+) terminally differentiated Th1 cells accumulate in the blood vasculature and do not control pulmonary infection. Here we examine CD4 T-cell differentiation and lung homing during primary Mtb infection of rhesus macaques. Mtb-specific CD4 T cells simultaneously appeared in the airways and blood B21-28 days post exposure, indicating that recently primed effectors are quickly recruited into the lungs after entering circulation. Mtb-specific CD4T cells in granulomas display a tissue-parenchymal CXCR3(+)CX3CR1(-)PD-1(hi)CTLA-4(+) phenotype. However, most granuloma CD4 Tcells are found within the outer lymphocyte cuff and few localize to the myeloid cell core containing the bacilli. Using the intravascular stain approach, we find essentially all Mtb-specific CD4 T cells in granulomas have extravasated across the vascular endothelium into the parenchyma. Therefore, it is unlikely to be that lung-homing defects introduced by terminal differentiation limit the migration of CD4 T cells into granulomas following primary Mtb infection of macaques. However, intralesional positioning defects within the granuloma may pose a major barrier to T-cell-mediated immunity during tuberculosis.