Deans J P, Wilkins J A, Caixia S, Pruski E, Pilarski L M
Department of Immunology, University of Alberta, Canada.
J Immunol. 1991 Dec 15;147(12):4060-8.
CD45, the leukocyte common Ag, has been shown to characterize T cell development both within the thymus and among peripheral T cells. The work reported here demonstrates that human multinegative (MN) thymocytes, depleted of cells bearing CD3, CD4, CD8, and CD19, express predominantly the high molecular mass CD45RA isoform, and lack low molecular mass CD45RB isoforms and CD45R0 as detected by immunofluorescence. By immunoprecipitation of surface-labeled CD45 molecules from MN thymocytes, a proportion of the CD45 is in fact of low molecular mass but does not include epitopes recognized by CD45R0, nor by CD45RB mAb specific for the p190. This suggests either glycosylation variants of CD45RB/CD45R0 undetectable by our mAb, or underglycosylated CD45RA. MN thymocytes lack TCR-alpha beta mRNA confirming their early developmental stage. Upon culture with IL-2 or with mitogenic combinations of anti-CD2/CD28 mAb, MN thymocytes differentiate to acquire CD3, TCR-alpha beta, and in some cases CD4 and/or CD8. We have predicted that maintenance of CD45RA and lack of CD45R0 expression is fundamental to generative thymic development. If correct, this demands that unlike peripheral T cells, differentiation of MN thymocytes should be accompanied by prolonged expression of high molecular mass CD45 isoforms. Analysis of CD45 isoform expression during MN thymocyte development confirms this prediction and indicates that expression of CD45RA is maintained, at increasing density, for at least 8 to 12 days of culture. Unlike peripheral blood T cells, this is accompanied by the gradual acquisition of firstly the p190 isoforms of CD45RB and later by CD45R0, resulting in a population of CD3+TCR-alpha beta cells coexpressing CD45RA/RBp190/R0. Dot blot analysis of mRNA from differentiating MN thymocytes indicates prolonged expression of mRNA encoding CD45 exons a, b, and c, again in contrast to peripheral T cells which lose all mRNA for alternatively spliced CD45 exons within the first 24 h poststimulation. This is discussed in the context of negative selection during thymic development and interconversion of T cell subsets.
白细胞共同抗原CD45已被证明可在胸腺内以及外周T细胞中表征T细胞的发育。本文报道的研究表明，去除携带CD3、CD4、CD8和CD19的细胞后的人多阴性（MN）胸腺细胞主要表达高分子量的CD45RA异构体，并且通过免疫荧光检测发现其缺乏低分子量的CD45RB异构体和CD45R0。通过对MN胸腺细胞表面标记的CD45分子进行免疫沉淀，发现一部分CD45实际上是低分子量的，但不包括CD45R0或针对p190的CD45RB单克隆抗体所识别的表位。这表明要么存在我们的单克隆抗体无法检测到的CD45RB/CD45R0糖基化变体，要么是CD45RA糖基化不足。MN胸腺细胞缺乏TCR-αβ mRNA，证实了它们处于早期发育阶段。在用IL-2或抗CD2/CD28单克隆抗体的促有丝分裂组合培养后，MN胸腺细胞分化并获得CD3、TCR-αβ，在某些情况下还获得CD4和/或CD8。我们预测维持CD45RA并缺乏CD45R0表达对于胸腺生成性发育至关重要。如果这是正确的，那么这就要求与外周T细胞不同，MN胸腺细胞的分化应伴随着高分子量CD45异构体的延长表达。对MN胸腺细胞发育过程中CD45异构体表达的分析证实了这一预测，并表明在培养至少8至12天的过程中，CD45RA的表达以增加的密度得以维持。与外周血T细胞不同，这伴随着首先逐渐获得CD45RB的p190异构体，随后获得CD45R0，从而产生一群共表达CD45RA/RBp190/R0的CD3⁺TCR-αβ细胞。对分化中的MN胸腺细胞的mRNA进行斑点印迹分析表明，编码CD45外显子a、b和c的mRNA表达延长，这再次与外周T细胞形成对比，外周T细胞在刺激后24小时内就会失去所有选择性剪接的CD45外显子的mRNA。本文将在胸腺发育过程中的阴性选择以及T细胞亚群相互转化的背景下对此进行讨论。
