Hb AA Research Articles

Tumor necrosis factor-alpha is undetectable in the plasma of SS patients with elevated Hb F.

Steady-state sickle cell disease (SCD) patients may have increased plasma levels of acute phase reactants and pro-inflammatory cytokines because of subclinical inflammation. We have estimated TNF-alpha levels in the plasma and in supernatants following peripheral blood mononuclear cell (PBMC) activation with phytohemagglutinin (PHA) in a group of Kuwaiti SCD patients using ELISA. The group consisted of 28 SS, 8 Sbeta-thal, and 2 SD patients all in steady state; 5 SS patients were studied during 7 episodes of painful crisis. The subjects were aged 2 to 16 years, with a mean of 7.3 +/- 3.5 years. The beta(S)-globin gene cluster haplotype, alpha-tha1 status, and spleen function were determined in the SS group using standard techniques. Most (82%) were homozygous for the Saudi Arabia/India haplotype and had elevated Hb F levels ranging from 15% to 35%. There were 24 controls (Hb AA or AS), of whom 14 were healthy and 10 were acutely ill at the time of the study. None of the children with SCD (either in steady state or crisis) had detectable plasma TNF-alpha, but four controls (3 acutely ill and one healthy) had levels ranging from 61.7 to 249.8 pg/mL. Following PHA stimulation most subjects responded with high levels of TNF-alpha, with the median level among the steady-state SS patients being significantly higher than that in the controls (both the acutely ill or healthy). It therefore appears that because of the mild disease among our Arab SS children, TNF-alpha is not detectable in their plasma in steady state; these children, however, had a significantly higher response than controls following PBMC activation.

Nitric oxide attenuates normal and sickle red blood cell adherence to pulmonary endothelium.

Increased adherence of sickle red blood cells (RBC) to endothelium is implicated as an initiating event of vaso-occlusion in sickle cell disease. Although much is known about the humoral influences of this interaction, there has been little investigation regarding endothelial contributions. Endothelial derived nitric oxide (NO) inhibits adhesion of platelets and leukocytes to endothelium and decreases expression of VCAM-1, an endothelial adhesion site implicated in sickle RBC/endothelial adherence. However, whether NO inhibits RBC adherence to endothelium is unexplored. We tested this hypothesis with endothelial monolayers exposed to RBC from normal (Hb AA) and sickle cell (Hb SS) volunteers in a parallel plate flow chamber. To decrease NO production, endothelial monolayers were exposed to 100 microM nitro-L-arginine (NLA), an inhibitor of nitric oxide synthase, resulting in an 87% increase in normal RBC adherence (P = 0.002). Because adherence of normal RBC to endothelium was low, the effect of DETA-NO, an NO donor, was tested after activation of endothelium with TNF-alpha increased adherence by 130% (P < 0.001). Subsequent addition of 2 mM DETA-NO produced a 75% decrease in adherence of normal RBC to endothelium (P = 0.03). At baseline, sickle RBC were significantly more adherent than normal RBC (P < 0.001) and DETA-NO decreased sickle RBC adherence by 54% (P = 0.04). Thus, NO inhibits both normal and sickle RBC adherence to endothelium. Strategies that enhance NO activity may be therapeutic in sickle cell disease.

The Frequency and Clinical Significance of Structural Haemoglobin Variants in Donor Blood at University of Maiduguri Teaching Hospital

The Haemoglobin (Hb) genotypes of 1672 healthy blood donors at the university of Maiduguri Teaching hospital (UMTH) during the year 1999 were analysed. Hb AA, AS and SC were detected in 78.94%, 21% and 0.06% of the donor population respectively. There is the need for strict application of Hb electrophoresis on all donor blood in order to detect rare cases of mild forms of sickle cell disease who may present as donors. All blood banks should label their blood units with the appropriate tags to indicate the Hb genotype (Hb AA or Hb AS) status of the donor; and clinicians must indicate on transfusion request forms whenever the use of Hb AA rather than HbAS blood is specifically indicated as may be the case in the management of sickle cell disease patients on exchange transfusion. In this way we can improve the efficacy of transfusion therapy in sickle cell disease and related conditions (Nig J Surg Res 2000; 2:127-130) KEY WORDS: Haemoglobin Electrophoresis, Blood Donor

GM-CSF in Sickle Cell Anemia Patients with Elevated Hb F

We estimated plasma GM-CSF levels in a group of 28 steady-state sickle cell anemia (SS) patients in Kuwait, using an ELISA technique. There were 24 age-matched Hb AA controls, 14 of whom were healthy while 10 were acutely ill at the time of the study. Five SS patients were also studied during 6 episodes of painful crisis. Among the SS patients, 82.1% were homozygous for the Saudi Arabia/India (SAI) haplotype with Hb F ranging from 15 to 35% and total Hb from 8.5 to 11 g/dl. Three patients (siblings) were SAI/Benin compound heterozygotes with Hb F of 9–23% and total Hb >10 g/dl. One patient each was homozygous for the Benin or the Bantu haplotype; they had Hb F <2% and total Hb of 6.6 and 7.2 g/dl, respectively. Four (14.3%) steady-state SS patients had detectable plasma GM-CSF ranging from 75 to 1,817.6 pg/ml. These included the 2 patients with Hb F <2.0% and 2 with the SAI/Benin compound heterozygotes with Hb F of 11 and 9%, respectively. Four (66.7%) SS patients in crisis, 6 (42.9%) healthy controls and 6 (60%) acutely ill controls had detectable plasma GM-CSF. A clearcut association of GM-CSF with Hb F level or degree of anemia in steady-state SS patients could not be established. The appearance of GM-CSF in the plasma of patients in crisis and also among control subjects raises the possibility that other factors are involved in the production of this cytokine in the subjects studied.

Pattern for alpha-thalassaemia in Yemeni sickle-cell-disease patients

A group of Yemeni patients with sickle-cell disease (SCD) and normal Hb AA individuals living in Riyadh were studied to determine the incidence of the alpha-gene molecular defect. Blood samples were obtained from 26 SCD patients and 19 controls (the Hb AA group). In the SCD patients the frequency of single alpha-gene deletion (-alpha/alpha alpha) was 0.346, compared to 0.263 in the Hb AA group. The frequency of two gene deletion (-alpha/-alpha) was 0.231 (0.0 for the Hb AA group). In one Hb AA case, a triple alpha-gene arrangement (alpha alpha alpha/alpha alpha) was found (frequency 0.053). The results suggest that alpha-thalassaemia occurs frequently in Yemeni SCD patients. Further studies to determine the overall frequency of alpha-thalassaemia in the Republic of Yemen would be of value for patient management.

Molecular studies on Yemeni sickle-cell-disease patients: Xmn I polymorphism

Our studies of the Saudi population have shown that in patients with mild presentation of sickle-cell disease (SCD) from Saudi Arabia's eastern region, the prevalence of polymorphic sites is high. However, the prevalence is very low in patients with severe SCD from the south-west of the country. We expanded these studies to a group of Yemeni patients with severe SCD, resident in Riyadh. We investigated a total of 60 chromosomes carrying the sickle-cell (Hb S) gene and 14 chromosomes carrying the Hb A gene. Amongst the Hb AA group, the prevalence was 42.9% and 57.1% for the presence (+) and absence (-) of Xmn I polymorphic sites. In the Hb SS individuals, the prevalence of Xmn I polymorphic sites was similar to the prevalence reported in the south-western region of Saudi Arabia.

Alpha thalassaemia in Yemeni children with sickle cell disease.

Alpha thalassaemia frequently occurs in several of the Middle Eastern populations. This study was conducted on 26 sickle cell disease (SCD) patients from Yemen and 19 normal children (Hb AA) living in Riyadh, Saudi Arabia. Blood samples were extracted by venepuncture, and haematological and biochemical parameters were estimated. DNA was extracted from the buffy coat and analysed for alpha-gene arrangement using Bam HI and Bgl II. The frequency of alpha-gene deletion in the total Yemeni group (26 SCD + 19 Hb AA) was 0.311 for one alpha-gene deletion (-alpha/alpha alpha) and 0.13 for two alpha-gene deletions (-alpha/-alpha). When separated on the basis of the Hb phenotype the alpha-gene deletion frequency was significantly higher (-alpha/alpha alpha = 0.346 and -alpha/-alpha = 0.231) in the SCD patients compared to the normal Hb AA group (-alpha/alpha alpha = 0.263 and -alpha/-alpha = 0). In the Hb AA group one child had triple alpha-gene arrangement (alpha alpha alpha/alpha alpha) giving an overall frequency of triple alpha-gene as 0.022. Haematological parameters showed variations in the SCD patients with and without alpha-gene deletion. This paper shows for the first time that alpha-gene deletion occurs in the Yemenis and the frequency is higher in patients with SCD. Further population-based studies are required to determine the exact frequency of the different types of alpha-thalassaemias in the overall Yemeni population.

Initiation of prenatal diagnosis of sickle-cell disorders in Africa.

We introduced prenatal diagnosis of SCD in Nigeria in order to meet a rising demand. Our approach and experience are documented as a guide to others in countries with similar problems. A cost-recovery fee charged only to sustain the service predictably limited access to it. Ultrasound-guided transcervical (TC) or transabdominal (TA) sampling of 124 chorionic villi was done from nine weeks' gestation. All couples carried the sickle trait (AS) and 52 (51 per cent) women had previously had children with sickle-cell anaemia. 72 samples were obtained by the TA and 52 by the TC route. 7.2 per cent miscarried after CVS but the miscarriage rate was significantly higher (p=0.023) after TC CVS (13.5 per cent) than after TA CVS (2.8 per cent) and also higher in the first 62 (11.3 per cent) than after the last 62 CVS (3.2 per cent). DNA analysis of CVS indicated Hb AA in 29 (23.4 per cent), AS in 67 (54 per cent) and SS in 23 (18.5 per cent). No result was obtainable in five subjects for technical reasons. 96 per cent of the women with SS fetuses terminated the pregnancies. The need for a standby source of electricity where supply is unreliable and for providing an equitable service to all couples at risk are highlighted.

Serum Immunoglobulins and IgG Subclasses in SS Patients with Saudi Arabia/India Haplotype

Objectives: This study investigates serum immunoglobulin fractions (IgG, IgA and IgM) and IgG subclasses (IgGScs; IgG1–4) in SS patients with the Saudi Arabia/India (SAI) haplotype. The influence of gender, Hb F levels, spleen function and coexistent α-thal trait were studied. Methods: Immunoglobulins and IgGScs were assayed using nephelometry. β^s-globin gene cluster haplotyping and α-globin genotyping were done using a combination of PCR and allele-specific oligonucleotide hybridization techniques. Results: Twenty-nine steady-state (i.e. not acutely ill) SS patients (23 SAI homozygotes and 6 SAI/Benin compound heterozygotes) and 34 healthy age- and sex-matched Hb AA and AS controls were studied. Mean serum IgG and IgA values were significantly higher in the patient group, while there were no significant differences in the mean IgGScs. The patient group was further subdivided depending on whether the spleen was normally visualized (group 1), partially visualized (group 2) or not visualized (group 3) on ^99mTc-labeled tin colloid scintigraphy. There was a significant sequential increase in mean IgG values from group 1 to group 3 but the reverse was true for IgM, while IgA showed no consistent trend. The mean levels of IgG1 and IgG3 were significantly higher in group 3 (p < 0.01). Hb F level did not influence immunoglobulins or IgGScs, but SS patients with coexistent α-thal trait tended to have lower IgG and IgG1 levels. Conclusions: Increased serum IgG is associated with poor splenic function and recurrent infections among SAI patients, while increased IgM is seen mainly in those with relatively normal splenic function.

Effects of gamma irradiation on red cells from donors with sickle cell trait.

Transfusion-associated graft-versus-host disease can be prevented by gamma irradiation of blood components. Red cells (RBCs) from sickle cell disease patients may exhibit oxidative changes of RBC membranes due to the instability of hemoglobin (Hb) S. Persons with sickle cell trait are eligible to donate blood, and 35 to 45 percent of their total Hb is Hb S. The effect of gamma irradiation on RBCs from such persons is of interest. RBCs from 12 donors with sickle cell trait (Hb AS) and from 12 with normal Hb (Hb AA) were studied. Each of the 24 RBC units was divided equally into two transfer bags via a sterile connecting device. One bag from each RBC unit received a 2500-cGy dose of gamma irradiation at its mid-plane and was stored at 4 degrees C; the second set of bags was stored without irradiation. For RBCs from 6 donors with Hb AS and 6 donors with Hb AA, units were irradiated on Day 7 and studied on Day 35 of storage (Group 1). For the RBCs from the other 6 donors with Hb AS and the other 6 donors with Hb AA, units were irradiated on Day 28 and studied on Day 42 of storage (Group 2). For Group 1 and Group 2, plasma potassium and plasma Hb concentrations were significantly higher and RBC ATP concentrations were slightly lower in the irradiated units than in the nonirradiated units. In Group 1 and Group 2, there were no significant differences in the plasma potassium or RBC ATP concentrations in either the irradiated or the nonirradiated units of RBCs from donors with Hb AS and donors with Hb AA. Plasma Hb concentrations were consistently lower in the units from donors with Hb AS, whether or not they were irradiated. However, in both groups, proportionally similar changes in plasma Hb concentration were detected when the irradiated Hb AS and Hb AA units were compared to nonirradiated Hb AS and Hb AA units. Gamma irradiation of RBCs from donors with Hb AS or with Hb AA resulted in comparable changes in plasma potassium, RBC ATP, and plasma Hb concentrations, although donors with Hb AS had lower plasma Hb. RBCs from donors with Hb AS subjected to 2500 cGy of gamma irradiation did not evidence a storage lesion greater than that seen in RBCs from donors with Hb AA.

The clinical manifestations of cerebral malaria among Nigerian children with the sickle cell trait.

In order to describe the interaction between haemoglobin type and the clinical manifestations of cerebral malaria, we studied 60 children aged between 6 and 60 months at University College Hospital, Ibadan, Nigeria. Haemoglobin AS individuals with cerebral malaria did not exhibit major differences in clinical and laboratory characteristics when compared with their haemoglobin AA counterparts. There were no deaths among the Hb AS children compared with an 18% mortality in the Hb AA group. Blood transfusion rates were higher in the AS than in the AA children (86% vs 44%). The higher transfusion rates in the AS group is consistent with in-vitro observations of sickling of parasitized red cells containing Hb S which in vivo would be cleared by the reticuloendothelial system. It is concluded that the clinical manifestations of cerebral malaria are essentially similar in children with haemoglobins AS and AA but the former have higher transfusion needs and are less likely to die.

A comparison of the dielectric behaviour of human haemoglobin SC with SS and AA in solution

Haemoglobin (Hb) SC is one of the most prevalent sickle-cell disorders. Patients with Hb SC are known to inherit a beta(S)-globin gene from one parent and a beta(C)-globin gene from the other. The radiofrequency dielectric properties of heterozygous Hb SC have been investigated and compared with those of homozygous Hb SS and AA in solution. The relative permittivity, , the dielectric loss factor, , and the energy dissipation factor, , of the different haemoglobin samples have been measured in the frequency range 0.1 - 50.0 MHz using a TF1245 Marconi Q-meter working in conjunction with a TF1246 oscillator at a room temperature of . The Hb SC samples were found to exhibit dielectric dispersions distinctly different from those of Hb SS and AA. The dielectric data were fitted to the Cole - Cole structural equation and the fitted parameters are presented. The results are discussed on the basis of the molecular structure and polymerization characteristics of the haemoglobins in solution.

Hydroxyurea-induced denaturation of normal and sickle cell hemoglobins in vitro.

Use of hydroxyurea (HU) to treat sickle cell disease is usually associated with increments in fetal hemoglobin (Hb F) production; however, in vitro studies show that HU may also induce hemoglobin denaturation. Whole blood samples from Hb AA, Hb AS, and Hb SS patients were treated in vitro with 100, 150, 200, 250, and 300 micrograms/mL HU, incubated at 30 degrees C for up to 12 days, and analyzed by high-performance liquid chromatography (HPLC). Hb AA levels show decrements of 91 to 14% with 100 micrograms/mL and 89 to 4% with 150 micrograms/mL after 12 days; 86 to 2% with 200 micrograms/mL after 10 days; 86 to 8% with 250 and 300 micrograms/mL after 8 days. Similar treatment and incubation times for Hb AS whole blood demonstrate that HU equally degrades the A and S components of Hb AS. A comparable approach for Hb SS whole blood samples, using a 300 micrograms/mL HU treatment, showed a hemoglobin denaturing pattern that went from 93% to 1% after 12 days. Globin chain analysis of these samples by reverse-phase HPLC showed that the denaturing effects occur mostly on the beta-globin chain.

A four base pair deletion 5' to the A gamma T gene is associated not only with decreased expression of the A gamma T-globin gene, but also of the G gamma-globin gene in cis.

A four base pair deletion 5' to A gamma T-globin gene at positions -222 to -225 has been reported to reduce the expression of this gene. To evaluate the prevalence and effect of this deletion, PCR-based methods were employed. The deletion had a gene frequency of 0.06 in a sample of African-American individuals with sickle cell trait, 0.18 in adult African-Americans with normal Hb AA, and 0.36 in caucasians. Seventy cord blood samples from African-American newborns with Hb AA were evaluated by both HPLC and PCR. The frequency of the A gamma T allele was 0.13. The A gamma T-globin chain was always present in a lower proportion than the A gamma I allele (70% of A gamma I), but the percentage of A gamma-globin was the same whether or not A gamma T was present. The total percentage of Hb F, however, was significantly lower in the group with the A gamma T allele (77.1% vs. 87.4%, P < 0.01). These results indicate that the four base pair deletion is not only associated with reduced expression of the A gamma T allele, but also of the G gamma allele in cis, further suggesting a possible role of this region in the modulation of the expression of the linked gamma-globin genes.

The Frequency of Glucose-6-Phosphate Dehydrogenase Phenotypes and Sickle Cell Genes in Al-Qatif Oasis

This study was conducted on a selected population of Al-Qatif in Eastern Saudi Arabia to determine the gene frequencies of glucose-6-phosphate dehydrogenase (G-6-PD) deficiency and sickle cell (HbS) genes and to study the extent of interaction between the two genes. A total of 960 blood samples collected from Saudi males (515) and females (445) attending the outpatient clinics and hospitals for minor illnesses were subjected to electrophoresis for separation of hemoglobin types and G-6-PD phenotyping and for spectrophotometric determination of G-6-PD activity. The prevalence of HbS heterozygotes was 25.9%, Hb S/b_-thalassemia was 1.563% and HbS homozygotes was 2.917%. The overall gene frequency of HbS was 0.1666. Severe glucose-6-phosphate dehydrogenase deficiency was encountered in a large percentage of the population with a frequency of 0.392 for G-6-PD Mediterranean and 0.0058 for G-6-PD-A- in the male population and 0.2020 and 0.0112 for G-6-PD Mediterranean and G-6-PD-A- in the female population respectively. Partial deficiency was encountered at a frequency of 0.0272 and 0.0697 in the male and female populations respectively. G-6-PD deficiency caused by G-6-PD Mediterranean occurred at a higher frequency in individuals with normal hemoglobin (Hb AA) (0.414 and 0.217 in males and females respectively) compared to the HbS heterozygotes (0.338 and 0.168 in males and females respectively) and HbS homozygotes and HbS bo-thalassemia cases (0.3125 and 0.1852 in males and females respectively). Compared to all areas of Saudi Arabia, Al-Qatif had the highest gene frequencies for HbS and G-6-PD deficiency genes.

Relevant laboratory findings in patients with sickle cell disease living at high altitude

In an attempt to assess the physiological changes that occur in a patient suffering from the sickle cell disease (SCD) and living permanently at a high altitude, hematological parameters (hemoglobin concentration, RBC count, reticulocyte count, MCH, MCHC, MCV, Hb S, F and A2 levels) and biochemical parameters (serum bilirubin, erythrocyte 2,3-DPG, serum iron, TIBC and haptoglobin levels) were measured in patients with two sickle cell syndromes (homozygous Hb SS and heterozygous Hb S/β°-thalassemia) matched with Hb AA normal controls living at an altitude of 3000m. These parameters were compared with values obtained in similar groups of subjects residing at sea level. Our results confirm that normal controls permanently residing at altitude have higher hemoglobin concentrations and erythrocyte 2,3-DPG levels than do normal counterparts living at sea level. Patients with SCD living permanently at high altitude show a marked increase in 2,3-DPG levels with little or no change in hemoglobin concentration. Normal serum iron and total iron binding capacity (TIBC) levels in our patients exclude iron deficiency as a possible reason for the poor expected erythropoietic response to altitude. We suggest that the marked rise in 2,3-DPG may be an important aid to oxygen delivery to tissues of SCD patients living at high altitude.

Structure of the Paramecium caudatum gene encoding the B-type of the major hemoglobin component

We have found the gene ( Hb) encoding the B-type of the major hemoglobin (Hb) component in the ciliated protist, Paramecium caudatum, stock K33 of syngen 3. Gene Hb, which encodes a protein consisting of 116 amino acids (aa), had the same sequence as the A-type Hb in this species, with the exception of 10 nucleotides (nt) reflecting 5 single-aa differences. The coding region was interrupted at the position between codons 62 and 63 by one short intron, which was comparable with the second intron of plant Hb in position, phase and nt sequence. The maximum alignment of the P. caudatum Hb aa sequence with the other globin sequences from prokaryotes and lower eukaryotes indicates that these globins can be classified into two groups: one consists of protist and cyanobacterial globins of about 120 aa, and the other consists of fungal and other bacterial globins of about 150 aa having a significant homology with higher eukaryotic Hbs. These proteins share more than 25% homology with one another in each group. Our finding of the P. caudatum Hb intron corresponding to the second intron of plant Hb suggests that all of the globin-encoding genes have a common origin, and that at least two groups had already existed in the globin-encoding gene before prokaryoteeukaryote radiation.

DNA polymorphism in the beta-globin gene cluster in Saudi Arabs: relation to severity of sickle cell anaemia.

Significant DNA polymorphisms have been reported in the beta-globin gene cluster of epsilon-G gamma-A gamma-psi beta-delta-beta-gene region, in normal (Hb AA) individuals and in patients with sickle cell anaemia (SCA). Investigations of the extent of the DNA polymorphisms in the beta A- and beta S-globin gene cluster using Hind III, Hinc II, Ava II, Xmn I, and Hpa I, revealed several associations with mild SCA. The correlation of the presence (+) or absence (-) of the restriction endonuclease site to clinical severity in patients homozygous for beta S-gene showed that the mild form of SCA was associated mainly (> 90%) with the Xmn I polymorphic site 5' to G gamma, and to a lesser extent with Hinc II polymorphic site 5' to epsilon and in the psi beta-gene, with Hind III polymorphic site in G gamma and Hpa I polymorphic site 3' to the beta-globin gene, while in the severe form of SCA these polymorphic sites were absent in most patients. The polymorphism in the beta-globin gene cluster was significantly related to the expression of the beta S-gene and clinical severity of SCA.

Sickle cell anaemia in Sudan: clinical findings, haematological and serum variables.

Ninety homozygous patients with Hb S haemoglobinopathy from Sudan were reported with respect to clinical findings, haematological and serum parameters. For comparison, 27 Hb AS heterozygous subjects and 28 Hb AA controls were investigated also. The patients showed an extreme type of illness presenting with severe clinical signs such as dactylitis, liver enlargement and cardiac complications. There was marked haemolytic anaemia (mean haemoglobin 66 g/l). Some patients also presented with low serum (S)-iron levels, indicating iron deficiency. S-bilirubin, S-ASAT, S-ALAT, S-GT and S-urate were notably raised, most probably as a consequence of haemolysis with liver involvement. The patients had lower S-calcium levels when compared with the AS and AA subjects. This may suggest a possible role of HB S in the production of this feature.

Abnormal neutrophil adhesion in sickle cell anaemia and crisis: relationship to blood rheology

Defects in neutrophil adhesion and migration may contribute to the susceptibility to infection seen in sickle cell anaemia (SCA). These dynamic defects may be influenced by abnormalities in blood rheology found in this disorder. A whole blood model was used to study neutrophil adhesion in SCA patients: neutrophil adhesion to protein coated glass was quantitated by measuring the rate of disappearance of neutrophils from heparinized whole blood circulating through a perfusion chamber. Twenty-three adult patients (Hb SS) were studied in asymptomatic steady state, of whom nine were also studied during pain crisis, both before and 4-7 d after conventional therapy. Red cell and granulocyte filterability and whole blood and plasma viscosity were also measured. The half-time for disappearance from the perfusion system (t1/2) of neutrophils from patients in the steady-state was 93.5 +/- 8.4 min, compared to 49.1 +/- 2.8 min in normal age-matched controls (P = 0.001). In crisis t1/2 was further prolonged to 170.0 +/- 16.1 min (P = 0.01 v. steady state). After therapy, t1/2 decreased to 57.0 +/- 4.5 min (P = 0.001 v. pre-therapy state and P = 0.009 v. steady state) and was comparable to Hb AA controls. These findings reveal a neutrophil adhesion defect in SCA which worsens in crisis but is corrected following supportive therapy. Red cell filterability (expressed as average resistance to flow and pore-clogging particles) and white cell filterability (expressed as pore-clogging particles) were also abnormal in SCA and were found to correlate with neutrophil adhesion. Plasma viscosity also correlated with adhesion t1/2. The defect appears to be related to abnormal blood flow properties in SCA but the rheological factors cannot fully explain either the steady-state defect or the marked changes in neutrophil adhesion during crisis.