O'Keefe G M, Nguyen V T, Benveniste E N
Department of Cell Biology, University of Alabama at Birmingham, 35294-0005, USA.
Eur J Immunol. 1999 Apr;29(4):1275-85. doi: 10.1002/(SICI)1521-4141(199904)29:04<1275::AID-IMMU1275>3.0.CO;2-T.
Microglia are the resident macrophages of the brain, and when activated, have functions including cytokine production, phagocytosis and antigen presentation. The class II MHC genes encode proteins that present antigenic peptides to helper T cells, leading to T cell activation and the development of an antigen-specific immune response. Class II MHC gene expression is strictly regulated by the class II transactivator (CIITA) transcription factor. In this study, we investigated the effects of various immunomodulatory cytokines on IFN-gamma induction of class II MHC and CIITA gene expression in microglia, both primary microglia and a murine microglial cell line, EOC 20. By flow cytometry analysis we show that IFN-gamma-induced surface expression of class II MHC molecules on EOC 20 cells can be inhibited by the cytokines TGF-beta1, IL-4 and IL-10, but not IL-13. Using a ribonuclease protection assay, we have found that TGF-beta1, IL-4 and IL-10 act by inhibiting the expression of IFN-gamma-induced CIITA mRNA and, in turn, class II MHC mRNA. TGF-beta1, IL-4, and IL-10 inhibition of IFN-gamma-induced CIITA mRNA accumulation was not due to destabilization of CIITA mRNA, suggesting an effect at the level of transcription. In primary murine microglia, IL-10 and TGF-beta1 inhibited IFN-gamma-induced CIITA and class II MHC expression. However, a discordant effect of IL-4 was noted in that IL-4 enhanced IFN-gamma-induced CIITA and class II MHC expression in primary microglia. Although some differences are observed between EOC 20 cells and primary microglia in terms of responsiveness to TGF-beta, IL-4 and IL-10, CIITA and class II MHC gene expression are coordinately modulated.
小胶质细胞是脑内的常驻巨噬细胞，激活后具有包括细胞因子产生、吞噬作用和抗原呈递等功能。II类主要组织相容性复合体（MHC）基因编码的蛋白质可将抗原肽呈递给辅助性T细胞，从而导致T细胞激活并引发抗原特异性免疫反应。II类MHC基因的表达受II类反式激活因子（CIITA）转录因子的严格调控。在本研究中，我们调查了多种免疫调节细胞因子对原代小胶质细胞和小鼠小胶质细胞系EOC 20中II类MHC和CIITA基因表达的IFN-γ诱导作用。通过流式细胞术分析，我们发现细胞因子TGF-β1、IL-4和IL-10可抑制IFN-γ诱导的EOC 20细胞表面II类MHC分子的表达，但IL-13无此作用。使用核糖核酸酶保护试验，我们发现TGF-β1、IL-4和IL-10通过抑制IFN-γ诱导的CIITA mRNA表达，进而抑制II类MHC mRNA的表达来发挥作用。TGF-β1、IL-4和IL-10对IFN-γ诱导的CIITA mRNA积累的抑制作用并非由于CIITA mRNA的不稳定，提示其作用于转录水平。在原代小鼠小胶质细胞中，IL-10和TGF-β1抑制IFN-γ诱导的CIITA和II类MHC表达。然而，观察到IL-4有不一致的作用，即IL-4增强原代小胶质细胞中IFN-γ诱导的CIITA和II类MHC表达。尽管在对TGF-β、IL-4和IL-10的反应性方面，EOC 20细胞和原代小胶质细胞之间存在一些差异，但CIITA和II类MHC基因的表达受到协同调节。
