Histopathology of Spleen.

(A) S1PL^+/+ spleen: Densely packed lymphocytes comprise the thick periarteriolar sheaths (PALS) in Wt mice. (B) S1PL^−/− spleen: There is severe depletion of T cells in the PALS. The lymphocytes in the PALS have been replaced by small numbers of macrophages, granulocytes, and plasma cells. B cell areas are still evident, with remaining lymphoid follicles and some germinal centers appearing more prominent due to lymphoid depletion of PALS. (C) S1PL^H/H spleen: The splenic white pulp contains essentially normal numbers and distributions of lymphocytes in the PALS and follicles. (D) S1PL^H/− spleen: Again, the splenic white pulp contains essentially normal numbers and distributions of lymphocytes in the PALS and follicles. H&E stain.