CD4 and infection: In the absence of infection, PBMCs remain as single cell monolayers but upon infection with live M.tb, PBMCs form granuloma-like structures that are up to 15 cell layers thick, contain macrophages, multinucleated giant cells, CD4 + and CD8 + T cells, B cells, NK cells, and intracellular M.tb (Fig S4A-D, Movies S1,S2)[20,21].