IL21 and HIV infectious disease: Remarkably, the expression levels of genes implicated in Tfh differentiation such as BCL6, BATF, and MAF were not affected by HIV infection, appearing slightly increased in Tfh and GCTfh from HIV+ samples (Fig 3B), while IL-21 and CXCL13 expression, two key mediators of Tfh function, were increased in Tfh from HIV+ spleens.