B cells need IL-21R for full maturation and progression of cGVHD. B10.BR recipients were transplanted with either WT BM or IL-21R KO BM and WT splenic (S) T cells. (A) Mice were evaluated for pulmonary function. (B) Whole spleen sections were stained with rhodamine-conjugated PNA, and the size of the PNA-positive sections was measured. Frequency of (C) Tfh and (D) GC B cells in the spleens of transplanted mice on D60. (E) Lung sections were stained with FITC-conjugated anti-mouse Ig, and the area of Ig deposition was measured, and (F) representative images. (G) Lungs of mice were stained with trichrome, and the ratio of collagen stain to total stain surrounding the bronchioles was measured with (H) representative images. Representative data from 3 experiments with n = 8 mice per group. *P < .05; **P < .01; ***P < .001.