Recent interest in therapies for sickle cell anemia based on elevating fetal Hb has made accurate estimates of the sparing effect offetal Hb (Hb F) and other non-sickle Hbs on sickle Hb (Hb S) polymerization essential. We have developed a technique, using HbCO as surrogate for HbO2, that enables us to assess the solubility of Hb S as a function of ligand saturation under conditions that mimic those of the sickling disorders. Equimolar mixtures of unliganded Hb S with Hb F or normal Hb A2 were isosoluble. Solubilities for equimolar mixtures with normal (Hb A) or abnormal (Hb C) Hbs were also identical but were lower than in the prior case. Thus, the sparing effect of both Hb F and Hb A2 should be considered in therapeutic strategies designed to modify Hb S polymerization. Hemolysates, stripped of 2,3-bisphosphoglycerate, from sickle cell disease patients with Hb (F + A2) levels varying from 6 to 25%, as well as from a sickle trait individual, were used to evaluate equilibrium solubiity as a function of ligand saturation over the range of pathophysiologic interest (25-70%). Our results show that the sparing effect of Hb (F + A2) increases relative to that of Hb A as ligand saturation increases, and that in the absence of ligand, '30% Hb (F + A2) is essentially isosoluble with the 60% Hb A of sickle trait. Although detailed knowledge of expected therapeutic benefits is confounded by the heterogeneity of Hb F distribution and other variables, these data should provide a framework for estimating likely clinical benefit from pharmacologic efforts to modulate globin gene expression.Sickle cell anemia exists in individuals who are homozygous for a point mutation (GAG --GTG) at codon 6 of the 3-globin gene, which results in a Glu-6 -* Val substitution in P-globin. are, thus, said to have a "sparing" effect on intracellular Hb S polymerization (3, 4). For Hbs F and A2, this solubilization can be described well with a model that assumes complete exclusion of either the homotetramer (a2-y2 or a2&2) or the hybrid heterotetramer (a238y or a2138) from the nascent polymer (5-7). For Hbs A and C, the data are compatible with exclusion of only homotetramers (a2I3A and a2K) from the polymer. Hybrid heterotetrameric forms (a2f3Sf3A and a2138S,c) appear to be incorporated into the polymer, but with a copolymerization probability roughly one-half that of Hb S (8-10). These copolymerization tendencies explain why the solubility enhancement induced by Hb F or A2 in admixture with Hb S is greater than that for Hb A or C.The solubilizing properties of various non-S Hbs have been established by use of a chemical reducing agent (dithionite) to completely deoxygenate mixtures of oxy-Hb S and the oxy form of other hemoglobins (Hb X), followed by centrifugation to fractionate the resulting semisolid gel into a tightly packed polymer pellet and a supernatant consisting of soluble Hb S and Hb X. The concentration of all Hb species in the supernatant is by definition the saturation concentration (csat), or equilibrium solubility, under g...

Intracellular hemoglobin S (HbS) polymerization is most likely to be the primary determinant of the clinical and biologic manifestations of sickle cell disease (SCD). Fetal hemoglobin (HbF) does not enter the HbS polymer and its intracellular expression in sickle erythrocytes inhibits polymerization. HbF levels, high at birth but decreasing thereafter, protect the newborn from the clinical manifestations of this hemoglobinopathy. We have measured the sequential changes in HbF, F reticulocytes, and F cells in the first 2 years of life in 25 children with SCD and compared the results with those obtained in 30 normal children (AA). We have also calculated HbF per F cell (F/F cell), the preferential survival of F cells versus non-F cells, as measured by the ratio F cells versus F reticulocytes (FC/FR) and polymer tendency at 40% and 70% oxygen saturation. HbF levels decreased from about 80.4% +/- 4.0% at birth to 9.2% +/- 2.9% at 24 months. During this time, we observed a regular decrease of the F reticulocytes and the F cells. The kinetics of the decline of F/F cell was comparable with the decline of HbF, rapid from birth (mean, 27.0 +/- 3.6 pg) to 12 months of age (mean, 8.5 +/- 1.5 pg) and then slower from 12 to 24 months of age (mean, 6.2 +/- 1.0 pg) in the SCD children. In the AA children, the decrease in HbF, due to changes in both numbers of F cells and F/F cell, was more precipitous, reaching steady-state levels by 10 months of age. Calculated values for mean polymer tendency in the F-cell population showed that polymerization should begin to occur at 40% oxygen saturation at about 3 months and increase progressively with age, whereas polymerization at 70% oxygen saturation would not occur until about 24 months. These values correspond to HbF levels of 50.8% +/- 10.8% and 9.2% +/- 2.9%, respectively, and F/F cell levels of 15.6 +/- 4.5 pg and 6.2 +/- 1.0 pg, respectively. In the non--F-cell population, polymerization was expected at birth at both oxygen saturation values. Three individuals had significantly greater predicted polymerization tendency than the remainder of the group because of early decreases in HbF. These individuals in particular, the remainder of the cohort, as well as other recruited newborns, will be studied prospectively to ascertain the relationship among hematologic parameters, which determine polymerization tendency and the various clinical manifestations of SCD.

Intracellular hemoglobin S (HbS) polymerization is most likely to be the primary determinant of the clinical and biologic manifestations of sickle cell disease (SCD). Fetal hemoglobin (HbF) does not enter the HbS polymer and its intracellular expression in sickle erythrocytes inhibits polymerization. HbF levels, high at birth but decreasing thereafter, protect the newborn from the clinical manifestations of this hemoglobinopathy. We have measured the sequential changes in HbF, F reticulocytes, and F cells in the first 2 years of life in 25 children with SCD and compared the results with those obtained in 30 normal children (AA). We have also calculated HbF per F cell (F/F cell), the preferential survival of F cells versus non-F cells, as measured by the ratio F cells versus F reticulocytes (FC/FR) and polymer tendency at 40% and 70% oxygen saturation. HbF levels decreased from about 80.4% +/- 4.0% at birth to 9.2% +/- 2.9% at 24 months. During this time, we observed a regular decrease of the F reticulocytes and the F cells. The kinetics of the decline of F/F cell was comparable with the decline of HbF, rapid from birth (mean, 27.0 +/- 3.6 pg) to 12 months of age (mean, 8.5 +/- 1.5 pg) and then slower from 12 to 24 months of age (mean, 6.2 +/- 1.0 pg) in the SCD children. In the AA children, the decrease in HbF, due to changes in both numbers of F cells and F/F cell, was more precipitous, reaching steady-state levels by 10 months of age. Calculated values for mean polymer tendency in the F-cell population showed that polymerization should begin to occur at 40% oxygen saturation at about 3 months and increase progressively with age, whereas polymerization at 70% oxygen saturation would not occur until about 24 months. These values correspond to HbF levels of 50.8% +/- 10.8% and 9.2% +/- 2.9%, respectively, and F/F cell levels of 15.6 +/- 4.5 pg and 6.2 +/- 1.0 pg, respectively. In the non--F-cell population, polymerization was expected at birth at both oxygen saturation values. Three individuals had significantly greater predicted polymerization tendency than the remainder of the group because of early decreases in HbF. These individuals in particular, the remainder of the cohort, as well as other recruited newborns, will be studied prospectively to ascertain the relationship among hematologic parameters, which determine polymerization tendency and the various clinical manifestations of SCD.

JOURNAL coccal disease have up to an 800 times greater risk of developing meningococcal disease, such as septicaemia, than those of the general population.]() The systemic treatment of a per son with a meningococcal conjunctivitis and the screening and treatment of their contacts with prophylactic antimicrobials is thus important. This case reaffirms the necessary practise of microbiologically investigating patients with conjunctivitis.

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