Rothstein D M, Yamada A, Schlossman S F, Morimoto C
Division of Tumor Immunology, Dana Farber Cancer Institute, Harvard Medical School Boston, MA 02115.
J Immunol. 1991 Feb 15;146(4):1175-83.
The CD45 Ag family is comprised of at least five isoforms generated by the alternative splicing of three exons encoded by a single leukocyte common Ag gene. These isoforms, differentially expressed on subsets of T cells, are widely believed to delineate maturational status. Thus, cells expressing the high molecular mass CD45RA+ isoforms (220 and 205 kDa) are believed to represent naive cells, whereas those lacking CD45RA and expressing high density CD45RO (180 kDa) represent memory cells. This is based on findings that after activation, CD45RA+ cells "convert" to the CD45RA- phenotype, losing CD45RA and gaining CD45RO. This conversion is believed to be both unidirectional and irreversible. We now report a strategy for the development of polyclonal CD45RA+ cell lines derived from peripheral blood CD4+CD45RA+ cells. However, in such cell lines, CD45RA expression was not constant, but varied cyclically with restimulation. After restimulation, CD45RA expression decreased significantly, nadiring on days 5 to 7. However, CD45RA was fully re-expressed by days 14 to 16. These cells coexpressed high density CD45RO, which did not vary through the stimulatory cycle. Cells sorted CD45RA- on day 7 of the cycle rapidly reexpress CD45RA. Metabolic labeling revealed that the 220 kDa CD45RA isoform is no longer synthesized. Synthesis of the 205 kDa (CD45RA) isoform decreased significantly early after stimulation, but then increased back to baseline after day 12. The 180-kDa (CD45RO) isoform followed an opposite pattern. Our results document that alternative splicing of the different CD45 isoforms is highly regulated after activation and that conversion from CD45RA+ to CD45RA- is neither unidirectional, nor irreversible.
CD45抗原家族由至少五种异构体组成，这些异构体是由单个白细胞共同抗原基因编码的三个外显子通过可变剪接产生的。这些异构体在T细胞亚群上差异表达，人们普遍认为它们可以界定成熟状态。因此，表达高分子量CD45RA +异构体（220和205 kDa）的细胞被认为代表幼稚细胞，而那些缺乏CD45RA并表达高密度CD45RO（180 kDa）的细胞代表记忆细胞。这是基于以下发现：激活后，CD45RA +细胞“转变”为CD45RA-表型，失去CD45RA并获得CD45RO。这种转变被认为是单向且不可逆的。我们现在报告一种从外周血CD4 + CD45RA +细胞中开发多克隆CD45RA +细胞系的策略。然而，在这样的细胞系中，CD45RA的表达并不恒定，而是随着再刺激呈周期性变化。再刺激后，CD45RA的表达显著下降，在第5至7天达到最低点。然而，到第14至16天，CD45RA完全重新表达。这些细胞共表达高密度的CD45RO，其在刺激周期中没有变化。在周期的第7天分选的CD45RA-细胞迅速重新表达CD45RA。代谢标记显示，220 kDa的CD45RA异构体不再合成。205 kDa（CD45RA）异构体的合成在刺激后早期显著下降，但在第12天后又回升至基线。180 kDa（CD45RO）异构体则呈现相反的模式。我们的结果表明，激活后不同CD45异构体的可变剪接受高度调控，并且从CD45RA +到CD45RA-的转变既不是单向的，也不是不可逆的。
