KD025 inhibits Stat3 phosphorylation and increases Stat5 activation decreasing the germinal center response. Day 60 spleens from B10.BR mice transplanted with B6 BM and T cells were analyzed for the (A) frequency of GCs in situ, (B) T follicular regulatory cell frequency, (C) T follicular helper cell frequency, and (D) germinal center B cell frequency. (E) Western blots of whole splenocytes for phosphorylation of Stat3 or Stat5 normalized to actin and (F) IRF4, RORγt, and Bcl6, which are quantified from 5 blots from 2 independent experiments in G and H, respectively. *P < .05; **P < .01; ***P < .001; ****P < .0001. Error bars represent SEM; data from 3 separate experiments with n = 8 per group.