Similar to Tfh responses during primary infection (Fig 5 A-C and Fig 9 D), Tfh responses during second P. chabaudi infection (Fig 9 E) and IFN-γ responses of CD4+ T cells during primary and second P. chabaudi infection (Fig 9 F and G) were not altered by the absence of IL-21 signaling. The gene discussed is CD4; the disease is infection.