ObjectiveTo investigate the alteration of Fc gamma receptors expressed on monocytes in childhood acute immune thrombocytopenia (aITP).Methods27 patients with aITP and 25 health controls were enrolled in this study.The expression of FcγR Ⅰ and FcγRⅢ on monocytes surface was determined by flow cytometry.Real-time PCR was performed to detect the levels of FcγR Ⅱ a and FcγR.Ⅱ b mRNA.The plasma concentration of IL-4 and IFN-γwas analyzed by ELISA.ResultsThe expression of FcγR I and FcγRⅢ on monocytes was significantly highet in ITP pationts than thatinhealth control group.Transcription levels of FcγR Ⅱ a mRNA and the ratio of FcγR Ⅱ a/Ⅱ b mRNA on monocytes were significantly elevated,while the inhibitory FcγR Ⅱ b mRNA was significant lower in aITP patients (P＜0.05) ; in comparison with healthy controls. After dexamethasone treatment,the stimulatory FcγR Ⅰ,FcγRⅢ and FcγR Ⅱ a mRNA were significantly decreased while inhibitory FcγR Ⅱ b mRNA was increased.(2)The higher levels of plasma IFN-y and lower IL-4 were to be found in aITP patients compared with healthy controls.Correlation analysis showed that the level of plasma IFN-γwas positively correlated with the elevated expression of FcγR Ⅱ a mRNA on monocytes,while the level of IL-4 was positively correlated with FcγRⅡ b mRNA.Conclusion The over expression of inhibitory FcγRs and the down-regulation of inhibitory FcγR Ⅱb mRNA on monocytes,and the imbalance of stimulatory and inhibitory FcγR might be involve in immunological pathogenesis of the acute ITP.The alteration levels of plasma pro-inflammatory cytokine IFN-γand anti-inflammatory cytokine IL-4 might be involved in imbalance expression of FcγR in acute ITP.Dexamethasone therapy could shift the balance between stimulatory and inhibitory FcγR toward inhibitory FcγR Ⅱ b in aITP patients.