TNF and sickle cell disease: To determine differences in TNF-α, IL-1β, IL-10, sICAM-1 concentrations, leg hypoxia and whole blood viscosity (WBV) at shear rates of 46 sec-1 and 230 sec-1 in persons with homozygous S sickle cell disease (SCD) with and without chronic leg ulceration and in AA genotype controls.