Mononuclear cells in sickle cell disease: subpopulations and in vitro response to mitogens

The subpopulations of mononuclear cells and the lymphocyte proliferative capacity following mitogen stimulation were studied in 22 patients with homozygous sickle cell (SS) disease and 25 controls with a normal haemoglobin (AA) genotype. The total number of lymphocytes in peripheral blood samples was higher in SS patients compared to controls. Expressed as a percentage of total lymphocytes, the number of B lymphocytes (detected by membrane immunoglobulin fluorescence) was normal and of T lymphocytes (identified by sheep erythrocyte rosetting) was slightly reduced in SS disease. Expressed in absolute numbers, both B and T lymphocytes were increased. Lymphocyte proliferation measured by tritium labelled thymidine incorporation following stimulation with phytohemagglutinin A, and concanavalin A was normal. Following pokeweed mitogen stimulation, thymidine incorporation was significantly increased in SS disease although normal when expressed as a stimulation index. These results do not suggest a major defect in cell mediated immunity in sickle cell disease. The number of circulating monocytes was increased in SS disease and correlated inversely with the number of reticulocytes (r = -0.58, p less than 0.005).