Lung Immunology Group, Infectious Diseases and Immunity, Department of Medicine, Imperial College, Hammersmith Hospital, Du Cane Road, London W12 0NN, UK.
BMC Biol. 2014 May 9;12:32. doi: 10.1186/1741-7007-12-32.
CD4 T lymphocyte activation requires T cell receptor (TCR) engagement by peptide/MHC (major histocompatibility complex) (pMHC). The TCR complementarity-determining region 3 (CDR3) contains variable α and β loops critical for pMHC recognition. During any immune response, tuning of TCR usage through progressive clonal selection occurs. Th1 and Th2 cells operate at different avidities for activation and display distinct transcriptional programs, although polarization may be plastic, influenced by pathogens and cytokines. We therefore hypothesized that CDR3αβ sequence features may intrinsically influence CD4 phenotype during progression of a response.
We show that CD4 polarization involves distinct CDR3α usage: Th1 and Th17 cells favored short TCR CDR3α sequences of 12 and 11 amino acids, respectively, while Th2 cells favored elongated CDR3α loops of 14 amino acids, with lower predicted affinity. The dominant Th2- and Th1-derived TCRα sequences with 14 amino acid CDR3 loops and 12 amino acid CDR3 loops, respectively, were expressed in TCR transgenics. The functional impact of these TCRα transgenes was assessed after in vivo priming with a peptide/adjuvant. The short, Th1-derived receptor transgenic T cell lines made IFNγ, but not IL-4, 5 or 13, while the elongated, Th2-derived receptor transgenic T cell lines made little or no IFNγ, but increased IL-4, 5 and 13 with progressive re-stimulations, mirrored by GATA-3 up-regulation. T cells from primed Th2 TCRα transgenics selected dominant TCR Vβ expansions, allowing us to generate TCRαβ transgenics carrying the favored, Th2-derived receptor heterodimer. Primed T cells from TCRαβ transgenics made little or no IL-17 or IFNγ, but favored IL-9 after priming with Complete Freund's adjuvant and IL-4, 5, 9, 10 and 13 after priming with incomplete Freund's. In tetramer-binding studies, this transgenic receptor showed low binding avidity for pMHC and polarized T cell lines show TCR avidity for Th17 > Th1 > Th2. While transgenic expression of a Th2-derived, 'elongated' TCR-CDR3α and the TCRαβ pair, clearly generated a program shifted away from Th1 immunity and with low binding avidity, cytokine-skewing could be over-ridden by altering peptide challenge dose.
We propose that selection from responding clones with distinctive TCRs on the basis of functional avidity can direct a preference away from Th1 effector responses, favoring Th2 cytokines.
CD4 T 淋巴细胞的激活需要 T 细胞受体（TCR）与肽/MHC（主要组织相容性复合体）（pMHC）结合。TCR 互补决定区 3（CDR3）包含对 pMHC 识别至关重要的可变α和β环。在任何免疫反应中，通过渐进性克隆选择来调整 TCR 的使用。Th1 和 Th2 细胞的激活亲和力不同，并表现出不同的转录程序，尽管极化可能是可塑的，受病原体和细胞因子的影响。因此，我们假设 CDR3αβ 序列特征可能会在免疫反应过程中内在地影响 CD4 表型。
我们表明，CD4 极化涉及不同的 CDR3α 利用：Th1 和 Th17 细胞分别偏爱短的 TCR CDR3α 序列 12 和 11 个氨基酸，而 Th2 细胞偏爱长的 CDR3α 环 14 个氨基酸，亲和力较低。具有 14 个氨基酸 CDR3 环和 12 个氨基酸 CDR3 环的优势 Th2 和 Th1 衍生的 TCRα 序列分别在 TCR 转基因中表达。在用肽/佐剂体内引发后，评估了这些 TCRα 转基因的功能影响。短的、Th1 衍生的受体转基因 T 细胞系产生 IFNγ，但不产生 IL-4、5 或 13，而长的、Th2 衍生的受体转基因 T 细胞系产生很少或没有 IFNγ，但随着逐渐的再刺激，产生增加的 IL-4、5 和 13，伴随着 GATA-3 的上调。来自 primed Th2 TCRα 转基因的 T 细胞选择了优势 TCR Vβ 扩张，这使我们能够生成携带偏向性 Th2 衍生受体异二聚体的 TCRαβ 转基因。用完全弗氏佐剂引发的 TCRαβ 转基因 primed T 细胞产生很少或没有 IL-17 或 IFNγ，但在用不完全弗氏佐剂引发后优先产生 IL-9。在四聚体结合研究中，这种转基因受体对 pMHC 的结合亲和力较低，极化的 T 细胞系对 Th17 的 TCR 亲和力> Th1> Th2。虽然 Th2 衍生的“伸长”TCR-CDR3α 和 TCRαβ 对的转基因表达明显产生了一种从 Th1 免疫偏向的程序，并且结合亲和力较低，但通过改变肽挑战剂量可以克服细胞因子偏斜。
我们提出，基于功能亲和力从反应性克隆中选择具有独特 TCR 的克隆可以引导 Th1 效应反应的偏好，有利于 Th2 细胞因子。
