Both wt→wt and wt→IA^bβ^−/− CD4 recipients develop histologic GVHD. (A) Representative histology (original magnification ×200). (B) Combined histology scores from 3 independent experiments. Each symbol is the score from an individual mouse; horizontal lines represent mean scores. P values are shown below the group labels. (C) Immunofluorescent staining of small intestine and skin from both wt→wt and wt→IA^bβ^−/− recipients of 129 CD4⁺ T cells. Blue indicates DAPI-stained nuclei; green, CD4⁺ cells; red, MHCII⁺ cells. Note infiltrating CD4⁺ cells in both bowel and skin of CD4 recipients, frequently adjacent to MHCII⁺ cells.