WT or signaling-selective APC-induced therapeutic improvement in cGVHD/BO involves decreased percentages of IL-17 and TFHs associated with reductions in GCs, Ig, and collagen deposition. cGVHD/BO was induced per Figure 1, and mice were given WT APC or signaling-selective 3A-APC or 5A-APC intraperitoneally from days 28 to 56. (A) Pulmonary function test results are shown. Spleens of BM-only (no cGVHD) or cGVHD mice, treated as indicated, were analyzed on day 56 by flow cytometry for IL-17⁺ T cells (B) and TFHs (C). (D) Immunofluorescent microscopy and quantitative imaging were performed for spleen GC size and frequencies. (E) Lung Ig deposition data using 4′,6-diamidino-2-phenylindole (blue) and anti-IgG-FITC (green) (BD Pharmigen). (F) Lung collagen deposition was analyzed by Masson’s trichrome staining. One experiment is shown, with 4 or 5 mice analyzed per group. Mean values ± standard error of the mean are shown. Original magnification ×200 for panels D-F. *P < .05, **P < .01, ***P < .001, ****P < .0001.