In previous studies a correlation with Tfh cells and infection was found (35–37), but each research group uses different phenotypic markers to define these circulating Tfh [e.g., CD4+CXCR5+ T cells (35), CD4+ICOS+CXCR3+CXCR5+ (36), CD4+CXCR5+CXCR3+PD1low/high (37)]. This evidence concerns the gene ICOS and infection.