Siegel Andrea M, Herskowitz Jeremy H, Speck Samuel H
Emory Vaccine Center and Department of Microbiology & Immunology, Emory University School of Medicine, Atlanta, Georgia, United States of America.
PLoS Pathog. 2008 Apr 4;4(4):e1000039. doi: 10.1371/journal.ppat.1000039.
Murine gammaherpesvirus 68 (MHV68) establishes long-term latency in memory B cells similar to the human gammaherpesvirus Epstein Barr Virus (EBV). EBV encodes an interleukin-10 (IL-10) homolog and modulates cellular IL-10 expression; however, the role of IL-10 in the establishment and/or maintenance of chronic EBV infection remains unclear. Notably, MHV68 does not encode an IL-10 homolog, but virus infection has been shown to result in elevated serum IL-10 levels in wild-type mice, and IL-10 deficiency results in decreased establishment of virus latency. Here we show that a unique MHV68 latency-associated gene product, the M2 protein, is required for the elevated serum IL-10 levels observed at 2 weeks post-infection. Furthermore, M2 protein expression in primary murine B cells drives high level IL-10 expression along with increased secretion of IL-2, IL-6, and MIP-1alpha. M2 expression was also shown to significantly augment LPS driven survival and proliferation of primary murine B cells. The latter was dependent on IL-10 expression as demonstrated by the failure of IL10-/- B cells to proliferate in response to M2 protein expression and rescue of M2-associated proliferation by addition of recombinant murine IL-10. M2 protein expression in primary B cells also led to upregulated surface expression of the high affinity IL-2 receptor (CD25) and the activation marker GL7, along with down-regulated surface expression of B220, MHC II, and sIgD. The cells retained CD19 and sIgG expression, suggesting differentiation to a pre-plasma memory B cell phenotype. These observations are consistent with previous analyses of M2-null MHV68 mutants that have suggested a role for the M2 protein in expansion and differentiation of MHV68 latently infected B cells-perhaps facilitating the establishment of virus latency in memory B cells. Thus, while the M2 protein is unique to MHV68, analysis of M2 function has revealed an important role for IL-10 in MHV68 pathogenesis-identifying a strategy that appears to be conserved between at least EBV and MHV68.
小鼠γ疱疹病毒68（MHV68）与人类γ疱疹病毒爱泼斯坦-巴尔病毒（EBV）一样，能在记忆B细胞中建立长期潜伏感染。EBV编码一种白细胞介素10（IL-10）同源物并调节细胞IL-10表达；然而，IL-10在慢性EBV感染的建立和/或维持中的作用仍不清楚。值得注意的是，MHV68不编码IL-10同源物，但病毒感染已被证明会导致野生型小鼠血清IL-10水平升高，而IL-10缺乏会导致病毒潜伏感染的建立减少。在此我们表明，一种独特的与MHV68潜伏相关的基因产物，即M2蛋白，是感染后2周观察到的血清IL-10水平升高所必需的。此外，原代小鼠B细胞中M2蛋白的表达驱动高水平的IL-10表达，同时IL-2、IL-6和MIP-1α的分泌增加。M2表达还被证明能显著增强LPS驱动的原代小鼠B细胞的存活和增殖。后者依赖于IL-10表达，这通过IL10 - / - B细胞对M2蛋白表达无反应以及添加重组小鼠IL-10可挽救M2相关增殖得以证明。原代B细胞中M2蛋白的表达还导致高亲和力IL-2受体（CD25）和激活标志物GL7的表面表达上调，同时B220、MHC II和sIgD的表面表达下调。细胞保留CD19和sIgG表达，表明分化为前浆细胞记忆B细胞表型。这些观察结果与之前对M2基因缺失的MHV68突变体的分析一致，这些分析表明M2蛋白在MHV68潜伏感染B细胞的扩增和分化中起作用——可能有助于在记忆B细胞中建立病毒潜伏感染。因此，虽然M2蛋白是MHV68特有的，但对M2功能的分析揭示了IL-10在MHV68发病机制中的重要作用——确定了一种似乎至少在EBV和MHV68之间保守的策略。
