Barritt L C, Turpen J B
Department of Cell Biology and Anatomy, University of Nebraska Medical Center, Omaha 68198-6395, USA.
Dev Comp Immunol. 1995 Nov-Dec;19(6):525-36. doi: 10.1016/0145-305x(95)00031-n.
The leukocyte common antigen, also known as CD45, is a structurally heterogenous molecule ranging in molecular weight from 180 to 220 kDa. CD45 belongs to a family of high molecular weight, cell surface glycoproteins expressed on all hematopoietic lineages with the exception of mature erythrocytes. In higher vertebrates, the highly conserved cytoplasmic domain of CD45 exhibits protein tyrosine phosphatase activity and has been implicated in lymphocyte activation through dephosphorylation of critical tyrosine residues on substrates associated with signal transduction pathways. The monoclonal antibody CL21 recognizes a high molecular weight determinant expressed on the surface of Xenopus leukocytes which was postulated to be a CD45 homologue. In order to determine if lymphocyte subpopulations expressed different molecular weight variants, splenic B cells were identified and isolated on the basis of surface IgM and the CL21 determinant expressed by these cells was compared to the determinant expressed by thymocytes. Immunoprecipitation revealed that IgM + B cells expressed a 220 kDa molecular weight variant whereas thymocytes and IgM-cells expressed a 180 kDa variant. Bone marrow myeloid cells, isolated on the basis of light scatter properties, expressed a determinant which ranged from 150 to 160 kDa. Dephosphorylation experiments utilizing p-nitrophenyl phosphate, 32P-labeled Raytide [tyr(P)], or Kemptide [ser(P)] as substrates demonstrated that immunoprecipitated CL21 antigen exhibited tyrosine specific phosphatase activity which was inhibited by sodium orthovanadate. Thus, data based on the presence of enzymatic activity and lineage restricted molecular weight variants support the hypothesis that the CL21 determinant is the amphibian homologue of mammalian CD45, and suggest that both structural and functional elements of CD45 have been conserved during vertebrate evolution.
白细胞共同抗原，也称为CD45，是一种结构异质的分子，分子量在180至220 kDa之间。CD45属于高分子量细胞表面糖蛋白家族，除成熟红细胞外，在所有造血谱系中均有表达。在高等脊椎动物中，CD45高度保守的胞质结构域具有蛋白酪氨酸磷酸酶活性，并通过使与信号转导途径相关的底物上的关键酪氨酸残基去磷酸化而参与淋巴细胞活化。单克隆抗体CL21识别非洲爪蟾白细胞表面表达的一种高分子量决定簇，推测其为CD45同源物。为了确定淋巴细胞亚群是否表达不同分子量的变体，根据表面IgM鉴定并分离了脾B细胞，并将这些细胞表达的CL21决定簇与胸腺细胞表达的决定簇进行比较。免疫沉淀显示，IgM + B细胞表达220 kDa分子量的变体，而胸腺细胞和IgM -细胞表达180 kDa的变体。根据光散射特性分离的骨髓髓样细胞表达一种分子量在150至160 kDa之间的决定簇。利用对硝基苯磷酸酯、32P标记的Raytide [tyr(P)]或Kemptide [ser(P)]作为底物的去磷酸化实验表明，免疫沉淀的CL21抗原表现出酪氨酸特异性磷酸酶活性，该活性被原钒酸钠抑制。因此，基于酶活性的存在和谱系限制的分子量变体的数据支持CL21决定簇是哺乳动物CD45的两栖动物同源物这一假设，并表明CD45的结构和功能元件在脊椎动物进化过程中均得到了保留。
