克隆了鳜T细胞表面受体CD4分子的cDNA序列并对其在组织/器官的表达进行了分析.鳜CD4分子的cDNA序列全长为2 356 bp,编码469个氨基酸.该CD4分子由4个免疫球蛋白样结构域(V1-C1-V2-C2)构成的胞外区、一个跨膜区和一个包含保守的CXC基序的胞内区组成.系统进化分析表明,鳜CD4分子与同属于鲈形目的鲈CD4分子聚为一支,与鲈的相似性最高(57％),与鲤的相似性较低(34％).序列比对分析显示,CD4分子胞外区存在多个保守性位点,如:C1结构域中的WTC基序、V2和C2结构域中的N-糖基化位点等.同鸟类和哺乳类不同的是,鳜CD4分子在V1结构域中缺少由半胱氨酸(Cys)残基对形成的二硫键,而在V2结构域中存在一个额外的二硫键,这可能会改变CD4分子的空间构象,进而影响到CD4与MHCⅡ的结合以及后续的抗原诱导的T细胞活化等.荧光定量PCR分析表明,CD4mRNA在鳜的胸腺中表达量最高,在脾脏中表达量最低.脂多糖腹腔注射8h后,CD4 mRNA在鳜的胸腺、脾脏和头肾中都呈显著的上调表达(P＜0.05).%The Cdna sequence of CD4 homologue was cloned from the mandarin fish Siniperca chuatsi. It consists of 2 356 bp,encoding 469 amino acids,and this molecule has a typical four Ig-like domains( Vl-Cl-V2-C2)and shares some fundamental conserved structures,I. E. WTC motif in D2 domain, Af-glycosylation site in D4 domian and the CXC motif in the cytoplasmic tail. Unlike avian and mammalian CD4 molecules, the mandarin fish CD4 sequence lacks the Cys pairs in the first Ig-like domain, but has a unique possible disulfide bond in the third domain. These differences suggest that mandarin fish CD4 molecule may have a different structure, which may in turn influence its binding with MHC II molecule and probably subsequent T-cell activation. The CD4 was expressed mainly in thymus, and following stimulation with LPS, its significant increase(P <0. 05) at Mrna level was observed 8 hours post injection in thymus, spleen and head-kidney. The mandarin fish CD4 shared a relatively high level of similarity(57% ) with that in sea bass Dicentrarchus labrax,and in the phylogenetic tree,the mandarin CD4 was clustered with that in sea bass. The cloning of CD4 in the mandarin fish may serve as a basis for further functional characterization of fish T lymphocytes.
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