FIG 2.

B cells do not require T cell-mediated help to facilitate protection from bone marrow failure as a result of Pneumocystis lung infection, but they promote extramedullary hematopoiesis as evidence for a bone marrow stress response. (A) Total bone marrow cell numbers of uninfected IFrag^−/− mice compared to those of IFrag^−/− mice infected with Pneumocystis murina on day 16 postinfection that were either left unreconstituted or that had received either total wild-type splenocytes or purified wild-type B cells prior to infection. Five mice per group were assessed. (B) H&E-stained histological sections of formalin-fixed and paraffin-embedded livers and spleens of mice in the groups compared, demonstrating evidence of extramedullary hematopoiesis in the form of cell nests in the liver (marked by an asterisk) and accumulation of megakaryocytes in the spleen (marked by arrows). For statistical analysis of data, a one-way ANOVA was performed followed by a Tukey posthoc test. Values that are significantly different are indicated as follows: *, P < 0.05; **, P < 0.01; ***, P < 0.001. Values that are not significantly different (n.s) are also indicated.