Distinct splicing of CD45 mRNA in activated rat gamma delta cytotoxic T lymphocytes.

Abstract

Previous studies have demonstrated tumor- and allo-specific cytotoxic gamma delta T lymphocytes in rats. In this report we define the surface phenotype of these T cell receptor (TCR) gamma delta+ T cells and demonstrate distinct CD45 mRNA splicing in activated gamma delta cytotoxic T lymphocytes (CTL). gamma delta T lymphocytes in the blood and the peritoneal cavity were TCR alpha beta-CD3+CD8 alpha+CD45RC+ but expressed variable levels of LFA-1 molecules. Normal peritoneal gamma delta T lymphocytes, peritoneal gamma delta T cells from rats injected with the bacterial superantigen staphylococcal enterotoxin A (SEA) as well as gamma delta T lymphocytes in peripheral blood were all LFA-1low. Peritoneal gamma delta T cells from tumor-, and allo-sensitized rats were either LFA-1low or LFA-1high and specific cytotoxicity was highly enriched in the LFA-1high subset. No cytolytic activity against SEA-presenting cells was recorded in gamma delta T cells from SEA-injected rats. Different isoforms of CD45 in T cells are generated by alternative mRNA splicing of exons 4, 5, 6 (or A, B and C, respectively) and the recently described alternate exon 7. CD45 splicing in sorted gamma delta T cells was evaluated utilizing reverse transcription polymerase chain reaction. Normal peritoneal gamma delta T cells expressed exon(578), exon(678), exon(78) and the extensively spliced exon(8) variant. Peritoneal gamma delta T cells from rats sensitized with irradiated syngeneic tumor cells, allogeneic cells or bacterial superantigen SEA as well as gamma delta T lymphocytes in peripheral blood contained the full-length exon(45678), as well as the exon(5678), exon(578), exon(678) and exon(78) splicing products. Notably, the exon(8) variant was also seen in peritoneal gamma delta T cells of SEA-sensitized rats. Sorted tumor-specific LFA-1high gamma delta CTL expressed exon(45678), exon(5678), exon(578), exon(678) and exon(78) CD45 splicing products whereas the non-cytolytic LFA-1low gamma delta T cell subset also contained exon(8) variant. In summary, it is concluded that antigen-specific TCR gamma delta+ CTL express high levels of LFA-1 and that the splicing machinery in these cytolytic cells favors expression of the exon(45678) and exon(5678) CD45 splicing products whereas the exon(8) variant is lost. TCR alpha beta+ CTL express high levels of LFA-1 but are devoid of the full-length exon(45678) splicing product. The different CD45 splicing patterns found in alpha beta CTL and gamma delta CTL indicate different molecular requirements in respect to CD45 during activation and differentiation of these T lymphocyte subsets.