T_FH cell dynamics in SIV and HIV infection

HIV targets CD4⁺ T cells, but two studies now report an accumulation of CD4⁺ T follicular helper (T_FH) cells in humans and primates with chronic HIV and SIV infection, respectively. The relative abundance of CXCR5⁺PD1^hi T_FH cells was increased in the lymph nodes of patients with HIV, with a large fraction of T_FH cells being HIV-specific. T_FH cell accumulation correlated with the presence of more germinal centre B cells and plasma cells, and increased IgG1 levels. Similarly, primates with chronic SIV infection had an increased percentage of CCR7^lowPD1^hiICOS^hiCD150^low T_FH cells. T_FH cell accumulation resulted from the differentiation of naive CD4⁺ T cells into T_FH cells, as a result of high IL-6 levels. T_FH cell accumulation in SIV-infected primates also correlated with high IgG levels, but how it may influence antibody maturation remains to be determined.