Image analysis studies of the degree of irreversible deformation of sickle cells in relation to cell density and Hb F level.

We analyzed, quantitatively by image analysis, the degree of irreversible deformation of red cells (SS cells) from patients with homozygous sickle cell disease, and studied the relationships among the degree of irreversible cell deformation, cell density, and Hb F level. SS cells from 25 patients (aged 1-36 years) whose Hb F levels ranged from 2.5% to 40.0%, were fully oxygenated and then were separated into four fractions by density centrifugation. Every fraction was studied for morphology and Hb F content. We found that the irreversible deformation of SS cells from the circulation occurred mainly by elongation and that the degree of elongation was extremely variable. We also found that in the cells of patients with Hb F levels < 20% the degree of irreversible elongation increases as cell density increases, suggesting that dehydration occurs concomitantly with irreversible elongation. Statistical analysis (Student t test) indicated that there were significant differences (P = 0.008 or < 0.001) in the degree of elongation among density-fractionated SS cells from patients with Hb F < 20%, although there was no significant difference (P > 0.1) among those from patients with Hb F > or = 20%. We also found that cell density increased as Hb F level of the density fraction decreased in all patients with Hb F < 20% but not always in those with Hb F > or = 20%. This suggests that cells with lower Hb F levels are selectively susceptible to dehydration. Furthermore, we found that the mean degree of irreversible elongation decreases linearly with increasing levels of Hb F and reaches the normal range at 21-24%. Since the degree of irreversible deformation of SS cells quantified by image analysis is directly related to cell density, and inversely to Hb F levels, mechanical stress or membrane damage caused by Hb S polymerization may be an important factor in the formation of dense cells in vivo.