| Background: Siglecs(sialic-acid-binding immunoglobulin-like lectins)are a trans-membrane protein family mainly expressed by immune cells,and in general, Siglecs are thought to negatively regulate cell function through glycan recognition. Siglec-7 is a member of CD33-related Siglecs that are predominantly expressed on natural killer(NK) cells and monocytes. Siglec-7 can suppress NK cell cytotoxicity through ligation with sialylated glycans. But the exact relationship of Siglec-7 expression and NK cell activities is still unknown. Previous study has showed that decreased Siglec-7 expression in HIV infection reflects dysfunction of NK cells, and the down-regulation is associated with HIV-1 viremia. But in chronic HBV infection, Siglec-7 expression on NK cells has not been reported.Objective: To determine the relationship of Siglec-7 expression and NK cell functions and to explore Siglec-7 expression on NK cells in chronic HBV infectionMethods and materials:(1) Experiment samples: Peripheral blood from healthy donors and chronic HBV infected patients.(2)Ficoll-Hypaque density gradient centrifugation was used to obtain peripheral blood mononuclear cells(PBMCs).(3) Flow cytometer was used to detect surface receptors and cytokines(4) CD107a- degranulation tests and IFN-γ-releasing tests were used to determine functions of different cell subsets.(5) Co-incubation with specific agonistic antibodies was used to detect the effect of crosslinking with ligands of Siglec-7 on NK cell functions.(6) Based on clinical data, chronic HBV infected patients were divided into four different phases, and flow cytometer was used to detect Siglec-7 expression on NK cells in peripheral blood from the four different phases.(7) Statistical analysis: Graph Pad Prism 5 was used to analyze experiment data; t test was used to analyze the normal distribution data, and non-parametric test was used to compare the non-normal distribution data.p<0.05 is thought to be significant.Results:(1) In peripheral blood from healthy donors, Siglec-7 was highly expressed on NK cells(82.6 ± 10.82 %), and there was a higher level of Siglec-7 expression on mature NK cells compared with immature NK cell subgroups; compared with Siglec-7- NK cells, Siglec-7+ NK cells expressed higher levels of activating receptors CD16(p=0.0349), CD38(p=0.0123), DNAM1(p=0.0024), NKp30(p=0.0122) and NKp46(p=0.0186), lower levels of inhibitory receptors NKG2A(p=0.024) and CD158b(p=0.0315).(2) Siglec-7+ NK cells had a stronger ability in CD107 a degranulation and IFN-γ releasing compared with Siglec-7- NKcells in peripheral blood from healthy donors.(3) Upon Co-incubation with specific agonistic antibodies, Siglec-7 inhibited CD107 a degranulation and IFN-γ producing of NK cells(p=0.0004, p=0.0125 respectively).(4)Siglec-7 expression on NK cells in chronic HBV infected patients(64.94±11.86 %) was decreased compared with that in healthy adults(82.6 ±10.82 %, p<0.01). And in the four immune phases of chronic HBV infection, there was a more significant decrease of Siglec-7 expression in the phase of immune tolerance(58.4±13.84 %) compared with in immune active phase(66.88±13.72 %, p<0.01), inactive phase(65.21±17.21 %,p<0.05) and immune relapsed phase(75.03 ± 17.48 %, p<0.01).(5) In peripheral blood from chronic HBV infected patients, Siglec-7+ NK cells had higher levels of CD107 a expression and IFN-γ releasing compared with Siglec-7- NK cells(p=0.0028, p=0.0103 respectively).Conclusions:(1) Siglec-7 is highly expressed on NK cells and is preferentially expressed on mature NK cells from peripheral blood of healthy adults.(2) Siglec-7+ NK cells have stronger cytotoxicity and ability to release cytokine than Siglec-7– NK cells.(3) Siglec-7 crosslinking suppresses NK cell functions.(4) Decreased Siglec-7 expression on NK cells in peripheral blood of chronic HBV patients, especially in immune tolerant phase, reflects dysfunction of NK cells, and the down-regulation of Siglec-7 is correlated with high levels of HBV viremia. |
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