Linehan L A, Warren W D, Thompson P A, Grusby M J, Berton M T
Department of Microbiology, University of Texas Health Science Center, San Antonio 78284, USA.
J Immunol. 1998 Jul 1;161(1):302-10.
Transcription of the germline C gamma1 and C epsilon Ig genes is believed to be a necessary prerequisite for isotype switching to IgG1 and IgE, respectively. IL-4 stimulation and ligation of CD40 can each independently induce low level germline gamma1 and epsilon transcription in murine B cells. Together these signals act synergistically to promote high level germline transcription and are normally required for T-dependent isotype switching to IgG1 and IgE. The STAT6 transcription factor has been suggested to play a critical role in IL-4-induced activation of germline C gamma1 and C epsilon genes. To directly assess the role of STAT6 in IL-4R- and CD40-mediated germline transcription and switching, we have analyzed these events in splenic B cells from STAT6-deficient mice. Our results demonstrate that IL-4 does not induce detectable levels of germline gamma1 or epsilon transcripts in STAT6-deficient B cells. Germline transcript expression induced by CD40 stimulation alone is unaffected, but synergism between CD40- and IL-4R-mediated signals is completely ablated. Switch recombination to S gamma1, as measured by digestion-circularization PCR, is dramatically reduced in STAT6-deficient B cells stimulated with CD40 ligand plus IL-4. Similarly, germline gamma1 transcript expression and switch recombination to S gamma1 are also impaired in STAT6-deficient B cells stimulated with IL-4, IL-5, and anti-IgD Abs conjugated to dextran, a model for T-independent type II responses. These results directly demonstrate a critical role for STAT6 in the IL-4-mediated activation of germline Ig gene transcription and switch recombination in nontransformed B cells.
生殖系Cγ1和Cε免疫球蛋白基因的转录被认为分别是向IgG1和IgE进行同种型转换的必要前提条件。IL-4刺激和CD40的连接各自都能独立诱导鼠B细胞中低水平的生殖系γ1和ε转录。这些信号共同发挥协同作用以促进高水平的生殖系转录，并且通常是T细胞依赖性向IgG1和IgE进行同种型转换所必需的。有人提出STAT6转录因子在IL-4诱导的生殖系Cγ1和Cε基因激活中起关键作用。为了直接评估STAT6在IL-4受体和CD40介导的生殖系转录及转换中的作用，我们分析了STAT6缺陷小鼠脾B细胞中的这些事件。我们的结果表明，IL-4在STAT6缺陷的B细胞中不会诱导可检测水平的生殖系γ1或ε转录本。单独由CD40刺激诱导的生殖系转录本表达不受影响，但CD40和IL-4受体介导的信号之间的协同作用完全消失。在用CD40配体加IL-4刺激的STAT6缺陷B细胞中，通过消化-环化PCR测量的向Sγ1的转换重组显著减少。同样，在用IL-4、IL-5和与葡聚糖偶联的抗IgD抗体刺激的STAT6缺陷B细胞中，生殖系γ1转录本表达和向Sγ1的转换重组也受损，这是一种非T细胞依赖性II型反应的模型。这些结果直接证明了STAT6在非转化B细胞中IL-4介导的生殖系免疫球蛋白基因转录激活和转换重组中起关键作用。
