Thymic IL-22 levels are reduced in mice with GVHD. (A-B) BALB/c (H-2^d) recipients were transplanted with 5 × 10⁶ TCD bone marrow (BM) cells from B6 mice (H-2^b) with or without 1 × 10⁶ BALB/c T cells to induce GVHD. (A) Total thymic cellularity on day 7 after transplant. (B) Thymic cellularity on day 7 and day 21 after transplant, analyzed by linear regression with slope comparison (1/slope for each line displayed on the graph). (C) B6 (H-2^b) recipients were transplanted with 5 × 10⁶ TCD BM cells from B10.BR mice (H-2^k) with or without 2 × 10⁶ B10.BR T cells to induce GVHD. Absolute levels of IL-22 were measured on day 7 post-BMT in B6 recipients or normal non-BMT controls (n = 10 per group). (D) BALB/c (H-2^d) recipients were transplanted with 5 × 10⁶ TCD BM cells from B6 mice (H-2^b) with or without 1 × 10⁶ BALB/c T cells to induce GVHD. Absolute levels of IL-22 were measured on day 7 post-BMT in BALB/c recipients or normal non-BMT controls (n = 9-10 per group). (E) Correlation of thymic cellularity and IL-22 levels in BMT recipients or normal controls from panels C and D. Left panel shows values from allo-BMT without T cells (blue circles and squares), indicating that after TCD BMT, the thymic cellularity and intrathymic IL-22 levels have a strong negative correlation. Right panel shows values from mice transplanted with allogeneic T cells (gray circles and squares), indicating that GVHD causes a loss of the correlation between thymic cellularity and the compensatory IL-22 response. Untransplanted normal controls are the same in both panels (white circles and squares). Bar graphs represent mean ± standard error of the mean (SEM) of at least 2 independent experiments. *P < .05; **P < .01; ***P < .001.