EXPRESSION OF CD45 ISOFORMS LACKING EXON-7, EXON-8 AND EXON-10

The CD45 exon usage pattern of various CD8(+) and CD4(+) T cell lines was studied. By using the reverse transcription-polymerase chain react ion (RT/PCR) and Southern analysis with exon specific or exon junction probes, we showed that all of the cytotoxic T cell lines and the majo rity of the helper T cells expressed the 789 isoform as a major splice variant. Expression of the splice product lacking exons 4-7 (isoform 89) was not as ubiquitous. All Th lines produced mRNA encoding this is oform, but in only three of the Tc lines was the 89 isoform detectable by RT/PCR. RNase protection assays with RNA isolated from normal CD8( +) splenic cells demonstrated the 89 splice product was present in low abundance. The relative abundance of the different isoforms in the th ymic lymphoma, BW5147, was determined through RNase protection analysi s. The 789 isoform predominates, representing approximately 75% of the CD45 mRNA whereas the 89 form constitutes about 24%. In addition: an isoform lacking exons 4-8 (isoform 9) also was detected and comprises approximately 1% of the total CD45 mRNA in this cell line. Finally: th ese studies demonstrate that exon 10 is also used as an alternatively spliced exon. (C) 1998 Elsevier Science Ltd. All rights reserved.