Figure 1 Immunohistochemical staining for the spleen of wild‐type (WT) (A–D) and Aα^0/0 mice (E–H) using antibodies for I‐A (A, E), CD4 (B, F), CD8 (C, G), and B220 (D, H). Many I‐A positive cells (A) were observed, mainly in the B220⁺ site (D) in the spleen of WT mice. Despite many B220⁺ cells (H), no I‐A positive cells were observed in Aα^0/0 mice (E). The number of CD8⁺ cells was similar between WT mice (C) and Aα^0/0 mice (G) but the number of CD4⁺ cells (F) was much smaller in Aα^0/0 mice than in WT mice (B). Original magnification: A–H ×100.