CD4 and Granuloma: They demonstrated that animals with pre-existing SIV infection had 1) lower CD4/CD8 T cell ratios across all tissue compartments including granulomas, 2) higher frequencies of CD4+ and CD8+ T cells expressing PD-1 or TIGIT (markers associated with immune activation) at sites of Mtb infection, and 3) fewer CD4+ T cells producing TNF in granulomas (28).