Changes in hemopoietic and regulator levels in mice during fatal or nonfatal malarial infections. I. Erythropoietic populations.

Erythroid precursors BFU-E and CFU-E and erythroblasts (ERB) were monitored in the marrow and spleen of mice during fatal or nonfatal malaria. Transient depletions of marrow CFU-E and ERB without modification of BFU-E or erythropoietin (Epo) levels were found as early events in fatal infections. Before anemia development, erythropoiesis was reduced in the bone marrow but increased in the spleen. During the anemic phase, for comparable levels of anemia, plasma Epo levels were elevated to a similar degree in fatal and nonfatal malaria. In the bone marrow, CFU-E increased twofold and BFU-E were usually reduced as expected in severe anemia. ERB populations increased but remained below or within normal values, suggesting an impairment of marrow erythropoiesis related to early events following infection. In contrast, in the spleen, ERB production was strongly simulated but amplification of ERB, CFU-E, and BFU-E populations was 2.5-fold lower in fatal than in nonfatal malaria. The results suggest that a defect in amplification of splenic erythropoiesis is a crucial determinant of the fatal outcome of malarial infection. This may have been mediated by a defective stem cell migration or multiplication. Some evidence obtained during recovery stages suggested that a factor(s) other than Epo may control splenic erythropoiesis during the anemia associated with malaria.