Some aspects of the pathophysiology of homozygous Hb CC erythrocytes

We have studied erythrocytes from homozygous CC patients in vitro and in perfused rat mesoappendix vasculature to answer some long-standing questions. By examination of wet whole blood preparations, and by comparing the cell distribution on isopycnic continuous density gradients of whole blood samples from a splenectomized CC patient with those from three intact CC patients, we have demonstrated the presence of a distinct crystal-containing band of cells that is present in the former, but totally absent from the latter. We conclude that Hb CC cells containing crystals circulate in Hb CC individuals, but in intact patients they are effectively removed by the spleen. By use of 31P nuclear magnetic resonance and viscosity measurements on cells, we have demonstrated that intracellular aggregation of hemoglobin C occurs on deoxygenation even when no crystal formation is detectable by morphological methods. These two observations are in apparent contradiction with the absence of clinical microcirculatory impairment found in both intact and splenectomized CC patients. The contradiction was resolved by rheological studies on isolated rat mesoappendix preparations and erythrocyte diameter measurements that lead to the conclusion that the hemorheological properties of CC cells in the microcirculation are nearly normal because their increased viscosity is offset by their smaller diameter and size.