Moreover, while the TFH master regulator (54) Bcl-6 (Figures 1D, E) and TFH-supporting receptor SLAMF1 (CD150) (55) (Figure 1F) were expressed at similar levels in the msLN BALB/c and Chi3l1-/- TFH cells, expression of ICOS, a key co-stimulatory molecule for TFH cells (39, 54, 56–58), was significantly decreased on the Chi3l1-/- CXCR5+PD-1hi TFH cells throughout infection (Figures 1G, H). Here, ICOS is linked to infection.