Overall, our findings suggest that high levels of PD-1 expression on CD4+ T cells in LN of rhesus macaques can serve as a valuable marker to identify Tfh cells and has implications for studying the role of Tfh cells in Human immunodeficiency virus (HIV), Simian immunodeficiency virus (SIV) and other infectious diseases that use the rhesus macaque model. This evidence concerns the gene CD4 and infectious disease.