In contrast, these changes in bone marrow erythropoiesis were not evident in B6.Rag2−/− mice, but could be fully reconstituted by adoptive transfer of IFNγ-producing but not IFNγ-deficient CD4+ T cells, mimicking the expansion of IFNγ-producing CD4+ T cells that occurs during infection in wild type mice. The gene discussed is CD4; the disease is infection.