Frequencies of peripheral blood myeloid cells in healthy kenyan children with α+ thalassemia and the sickle cell trait

The high frequencies of both + thalassemia and the sickle cell trait (hemoglobin AS (HbAS)) found in many tropical populations are thought to reflect selection pressure from Plasmodium falciparum malaria. For HbAS, but not for + thalassemia, protection appears to be mediated by the enhanced phagocytic clearance of ring-infected erythrocytes. We have investigated the genotype-specific distributions of peripheral blood leukocyte populations in two groups of children living on the coast of Kenya: a group of healthy P. falciparum parasite-negative children sampled at cross-sectional survey during a period of low malaria transmission, and a group of children attending the hospital with acute malaria. We report distinctive distributions of peripheral blood myeloid dendritic cells and monocytes in children with + thalassemia and HbAS during healthy periods and disease, and suggest ways in which these might relate to the mechanisms of protection afforded by these conditions.