Effect of Trypanosoma brucei brucei on erythropoiesis in infected rats

Anemia generated from African trypanosome infection is considered an important symptom in humans and in domestic animals. In order to recover from anemia, the process of erythropoiesis is essential. Erythropoiesis is affected by erythropoietin (EPO), an erythropoietic hormone, supplying iron and inflammatory and proinflammatory cytokines. However, the role of these factors in erythropoiesis during African trypanosome infection remains unclear. In the present study, we analyze how erythropoiesis is altered in anemic Trypanosoma brucei brucei (interleukin-tat 1.4 strain [ILS])-infected rats. We report that the packed cell volume (PCV) of blood from ILS-infected rats was significantly lower 4 days after infection, whereas the number of reticulocytes, as an index of erythropoiesis, did not increase. The level of EPO mRNA in ILS-infected rats did not increase from the third day to the sixth day after infection, the same time that the PCV decreased. Kidney cells of uninfected rats cultured with ILS trypanosome strain for 8 hr in vitro decreased EPO mRNA levels. Treatment of both ILS and cobalt chloride mimicked hypoxia, which restrained the EPO-production-promoting effect of the cobalt. Messenger RNA levels of β-globin and transferrin receptor, as markers of erythropoiesis in the bone marrow, also decreased in ILS-infected rats. Levels of hepcidin mRNA, which controls the supply of iron to the marrow in liver, were increased in ILS-infected rats; however, the concentration of serum iron did not change. Furthermore, mRNA levels of interleukin-12, interferon-γ, tumor necrosis factor-α, and macrophage migration inhibitory factor in the spleen, factors that have the potential to restrain erythropoiesis in bone marrow, were elevated in the ILS-infected rats. These results suggest that ILS infection in rats affect erythropoiesis, which responds by decreasing EPO production and restraining its function in the bone marrow.