Hydroxycarbamide reduces eosinophil adhesion and degranulation in sickle cell anaemia patients.

Inflammation, leucocyte and red cell adhesion to the endothelium contribute to the pathogenesis of sickle cell anaemia. Neutrophils appear to be important for vaso-occlusion, however, eosinophils may also participate in this phenomenon. The role of eosinophils in the pathophysiology of sickle cell anaemia (SCA) and the effect of hydroxycarbamide (HC) therapy on the functional properties of these cells are not understood. Patients with SCA and those on HC therapy (SCAHC) were included in the study. SCAHC individuals presented significantly lower absolute numbers of eosinophils than SCA. Furthermore, SCAHC eosinophils demonstrated significantly lower adhesive properties, compared to SCA eosinophils. SCA and SCAHC eosinophils presented greater spontaneous migration when compared with control eosinophils. Baseline eosinophil peroxidase and reactive oxygen species release was higher for SCA individuals than for control individuals, as were plasma levels of eosinophil derived neurotoxin. SCAHC eosinophil degranulation was lower than that of SCA eosinophil degranulation. Eotaxin-1 and RANTES levels were higher in the plasma of SCA and SCAHC individuals, when compared with controls. These data suggest that eosinophils exist in an activated state in SCA and indicate that these cells play a role in the vaso-occlusive process. The exact mechanism by which HC may alter SCA eosinophil properties is not clear.

IFN-ß, IFN-γ, and TNF-α decrease erythrophagocytosis by human monocytes independent of SIRP-α or SHP-1 expression.

BACKGROUND: Many cases of autoimmune hemolytic anemia have been reported after viral infection. Phagocyte activation and accompanying erythrophagocytosis are thought to result from proinflammatory cytokines released during viral infection. SIRP-α (signal regulatory protein-α), a receptor expressed on phagocytes, inhibits phagocytosis when bound to CD47 on the erythrocyte membrane. Ligation with CD47 results in SHP-1 recruitment to SIRP-α and dephosphorylation of specific downstream substrates involved in phagocytosis. SIRP-α ligation by CD47 may be inhibited by proinflammatory cytokines. OBJECTIVES: The aim of this work was to evaluate the effect of IFN-ß, IFN-γ, and TNF-α on erythrophagocytosis and assess the effect on expression of SIRP-α and SHP-1 in human monocytes. MATERIALS AND METHODS: Monocytes were cultured ex vivo with IFN-ß or IFN-γ/TNF-α. Erythrophagocytosis was determined by flow cytometry. SIRP-α and SHP-1 gene expression was determined by real time-PCR, while SIRP-α and SHP-1 protein expression was determined by western blot. RESULTS: Erythrophagocytosis by monocytes significantly decreased after treatment with either IFN-ß or IFN-γ/TNF-α. Monocytes cultured with IFN-γ/TNF-α showed increased SIRP-α gene and protein expression and SHP-1 gene expression. Monocytes cultured with IFN-ß did not show any alteration in SIRP-α or SHP-1 expression. CONCLUSION: We conclude that IFN-ß and IFN-γ/TNF-α decrease erythrophagocytosis by human monocytes in vitro, and this effect does not apparently require an increase in SIRP-α or SHP-1 expression.