DIFFERENT TYPES OF IN-VIVO INDUCED CYTOLYTIC T-LYMPHOCYTES ARE ALL LFA-I(HIGH) 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 resp ectively), the CD45 cell surface glycoprotein is structurally heteroge neic in lymphoid cells of different lineage or stage of activation. Pr evious studies show that in vivo induced allo- and superantigen reacti ve rat cytolytic T lymphocytes (CTL) preferably belong to the CD45RC(l ow) subset, whereas tumour selective CTL express high amounts of CD45R C cell surface molecules. In this paper, reverse transcription polymer ase chain reaction technique (RT-PCR) was utilized to evaluate CD45 is oform expression of rat lymphoid cells and in vivo activated rat CTL w ith distinct specificity and CD45RC profile. Cells from lymphoid organ s 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 CD45RC(low ) expressed exon(78), exon(578) and exon(8), whereas TCR alpha beta(+) CD8(+) CD45RC(high) cells expressed exon(78), exon(578), exon(5678) an d full-length exon(45678). Triple-colour staining indicated high expre ssion of LFA-1 in the cytotoxic CD45RC(intermediate) and CD45RC(low) c ells, and low expression of LFA-1 in CD45RC(high) non-cytotoxic cells from allo- and superantigen activated rats. In contrast, tumour activa ted TCR alpha beta(+)CD45RC(high) cells were divided in LFA-1(high) an d LFA-1(low) subsets, and sorting of these subsets revealed that tumou r-selective cytotoxicity was confined to the LFA-1(high) effector cell subset. Furthermore, it was evident that the LFA-1(high) effector cel l subset expressed high levels of exon(5678), exon(578) and exon(78) i soforms and, in contrast to the LFA-1(low) subpopulation, lacked expre ssion of exon 4 containing full-length CD45 mRNA transcript. In conclu sion it is demonstrated that In vivo induced effector CTL are all LFA- 1(high) and express extensively spliced CD45 isoforms but exhibit dist inct expression of surface CD45RC. The variable CD45 profile detected in differentiated CTL with distinct antigen selectivity indicates func tional diversity of the different CD45 isoforms.