Publication Only: Sickle cell disease
Bacterial infections are a frequent cause of acute morbidity and sometimes mortality in sickle cell disease (SCD). Splenic dysfunction alone does not explain the susceptibility to specific organisms e.g., Staphylococcus aureus and Klebsiella as shown in some studies; suggesting that the splenic dysfunction is not the only explanation and that neutrophil dysfunction may be present. Neutrophils destroy microbes by producing a burst of reactive oxygen species (ROS) (respiratory burst) in response to bacterial components, as well as to phorbol-myristate-acetate (PMA). Some studies have shown that the state of chronic hemolysis in SCD impairs the ability to develop neutrophils to mount a bactericidal oxidative burst, and hence increasing susceptibility to bacterial infections.
to assess the neutrophil oxidative burst in SCD patients and explore the relation to markers of hemolysis.
Twenty-seven hydroxyurea naïve children and adolescents with SCD (mean age 11.1 ± 3.9 years) were enrolled from Pediatric Hematology Clinic at Ain Shams University Children's Hospital. They were compared to 26 age- and sex-matched healthy controls. Patients were studied stressing on transfusion history, chelation therapy, serum ferritin, hematological profile, markers of hemolysis and serum haptoglobin. Neutrophil oxidative burst assay was performed using DHR based flow cytometry.
Eleven (40%) out of the 27 patients had HBSS while 16 (60%) patients were sickle thalassemias. Six patients (22.2%) were splenectomized. Severe vaso-occlusive crisis and acute chest syndrome were found in 22.2% and 18.5% of patients, respectively. Four (14.8%) patients had evidence of stroke. Bone fractures and avascular necrosis were found in 5.5% and 11.1 % of patients, respectively. Most of the studied patients were on chelation therapy, either as monotherapy or combined chelation (37% each). White blood cell count and reticulocytic count were significantly higher in SCD patients as compared to healthy controls (P = 0.03 and <0.01 respectively). All subjects, whether SCD or controls showed a normal neutrophil oxidative burst response to PMA-stimulation. Unstimulated and PMA stimulated rhodamine fluorescence were comparable in SCD patients and controls, indicating normal basal production of reactive oxygen species, and normal oxidative burst in SCD patients (P = 0.09). We did not demonstrate any correlation between markers of hemolysis including reticulocytic count, indirect bilirubin, LDH, serum haptoglobin and DHR response in the SCD group.
Neutrophils in SCD patients can mount a normal oxidative burst in response to PMA stimulation. This data excludes the role of impaired neutrophil oxidative burst as a risk for bacterial infections in SCD.