IFN-β, 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-β, 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-β 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-β 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-β did not show any alteration in SIRP-α or SHP-1 expression.
CONCLUSION: We conclude that IFN-β 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.