CD4 and infection: Furthermore, while the ratio of Th1 to Tfh cells was similar in SLOs early after infection (3–5 dpi) during the primary and secondary responses, despite the likely rapid clearance of Lm antigen, the secondary 2W-specific CD4+ T cell response surprisingly (7) favored a Tfh phenotype between days 7 and 21 post-infection (Figures 2F–H).