Different types of in vivo induced cytolytic T lymphocytes are all LFA-Ihigh and lack CD45 exon 4 (CD45RA) but show distinct CD45RC profiles.

Due to alternate mRNA splicing of exons 4, 5 and 6 (or A, B and C respectively), the CD45 cell surface glycoprotein is structurally heterogeneic in lymphoid cells of different lineage or stage of activation. Previous studies show that in vivo induced allo- and superantigen reactive rat cytolytic T lymphocytes (CTL) preferably belong to the CD45RClow subset, whereas tumour selective CTL express high amounts of CD45RC cell surface molecules. In this paper, reverse transcription polymerase chain reaction technique (RT-PCR) was utilized to evaluate CD45 isoform expression of rat lymphoid cells and in vivo activated rat CTL with distinct specificity and CD45RC profile. Cells from lymphoid organs expressed six CD45 mRNA isoforms, exon(45678), exon(5678), exon (578), exon(678), exon(78) and a novel extensively spliced exon(8) variant. In vivo activated TCR alpha beta + CD8+ cells sorted as CD45RClow expressed exon(78), exon(578) and exon(8), whereas TCR alpha beta + CD8+CD45RChigh cells expressed exon(78), exon(578), exon(5678) and full-length exon(45678). Triple-colour staining indicated high expression of LFA-1 in the cytotoxic CD45RCintermediate and CD45RClow cells, and low expression of LFA-1 in CD45RChigh non-cytotoxic cells from allo- and superantigen activated rats. In contrast, tumour activated TCR alpha beta +CD45RChigh cells were divided in LFA-1high and LFA-1low subsets, and sorting of these subsets revealed that tumour-selective cytotoxicity was confined to the LFA-1high effector cell subset. Furthermore, it was evident that the LFA-1high effector cell subset expressed high levels of exon(5678), exon(578) and exon(78) isoforms and, in contrast to the LFA-1low subpopulation, lacked expression of exon 4 containing full-length CD45 mRNA transcript.(ABSTRACT TRUNCATED AT 250 WORDS)