CD4 and infection: To investigate the determinants of HIV transmission from infected CD4+ T lymphocytes to macrophages (Mf), PBMC-derived Mf were first polarized into M0, M1, or M2 phenotypes and then co-cultured with Jurkat (Jk) cells: mock-infected (Jk-Mock), infected with R5- (Jk-R5) or X4-tropic (Jk-X4) HIV strains (see experimental timeline in Supplementary Figure S1A), harboring comparable infection rate (25.5 ± 2.7% and 24.0 ± 6.4%, respectively; Supplementary Figure S1B).