CD9 and infection: Titration assays showed that infection rates increased progressively with higher Jurkat-R5 to macrophage (Jk-R5:Mf) ratios in cocultures, reaching approximately 36.5 ± 9.2% p24+ macrophages at a 2:1 ratio and remaining detectable (~2.5 ± 1.9%) even at a 1:1, 000 ratio.