Effects of murine cytomegalovirus infected mouse embryonic fibroblasts on the proliferation and activation of co-cultured regulatory T cells / 中华传染病杂志

ABSTRACT

Objective To explore the effects of murinecytomegalovirus(MCMV)infected mouse embryonic fibroblasts(MEF)on the proliferation and activation of regulatory T cell in vitro. Methods A co-culture system of T cell and MCMV infected MEF(T-MEF MCMV)was established.The viral load of supernatant was determined by plaque assay.The proliferation of T cells was observed with cell counting.The proportion of CD4+ CD25+ cells was measured by flow cytometry.The levels of Foxp3 protein were measured by Western blot.Reverse transcription polymerase chain reaction(RT-PCR)assay was utilized tO determine whether MCMV infection of MEF influenced the level of transforming growth factor(TGF)-β mRNA.The level of TGF-β protein in supernatant was measured by double-antibody sandwich enzyme linked immunosorbent assay(ELISA).The difference between T-MEF MCMV group and control group was assessed by one-way ANOVA.Results When T cells were co-cultured with MCMV infected MEF for 1 day and 3 days,the viral load in supernatant decreased.But when co-culture lasted for 6 days,the antiviral effect obviously diminished,as the viral load[(5.58±0.67)×105 PFU/mL]of the experimental group showed no statistic difference with MEF MCMV control group[(6.05±0.34)×105PFU/mL].When co-cultured with MCMV infected MEF for 3 days,T cell increased from pre-culture level of[(2.02±0.05)×106/mL]to(2.25± 0.13)×106/mL(P＜0.05).But when co-culture lasted for 6 days,the number of T eelI returned to (2.08±0.14)×106/mL,which had no statistic difference with that of co-culture for 3 days system. Both the expressions of Foxp3 protein and the proportion of CD4+ CD25+ Foxp3+ Treg cells in T-MEF MCMV group were up-regulated as the infection time extended,which were two times and three times of the control group level,respectively.The mRNA level(A value)of TGF-β in MCMV infected MEF increased from baseline of 1.09±0.13 to 3.15±0.54 on day 3 after infection.The expression of TGF-β in supernatant 3 days after infection was(3.85±0.32) μg/L,which was significantly higher than that before infection[(1.74±0.14)μg/L,P＜0.05].Conclusions Activated T cells have antiviral effect.However,the function of T cells is rapidly inhibited after activation,which may be due to the expression of Foxp3 mRNA induced by MCMV infected MEF and increased CD4+ CD25+ Treg proportion of the co-cultured T cells.TGF-β level is significantly increased after CMV infection,which may be an important mechanism of Treg proliferation.MCMV may manipulate Treg to evade specific immune elimination and,as a result,to cause CMV replication.