Detection of CD45iota mRNA in murine Th1 but not Th2 clones

CD45, a prototype of the receptor-like protein tyrosine phosphatase (PTPase ) family, is one of the essential molecules in signal transduction through T cell receptors. Because at least 8 types of CD45 isoforms can potentially be produced by alternative mRNA splicing of exons 4, 5, and 6, the analyse s at the transcription and protein levels of CD45 during the development an d differentiation of T cells have been performed using RT-PCR and isoform-s pecific monoclonal antibodies, respectively. We report here that the ninth and smallest isoform of CD45, designated as CD45iota (CD45 iota), which is alternatively spiced from exons 4, 5, and 6 as well as exon 7, is present i n the fetal thymus and splenic T cells of mice, and in murine Th1 clones, b ut not in Th2 clones. The expression of full-length CD45 iota mRNA as the f unctional CD45 PTPase was confirmed by RT-PCR analysis. Furthermore, the ex pression vector of CD45 iota was constructed, and its expression was detect ed in combination with anti-pan CD45 mAb and our newly established anti-LAR /CD45 PTPase domain mAb. These results suggested chat CD45 iota might be an important isoform of CD45 for differentiation signaling of Th cells, and m ight be used as a marker to distinguish between Th1 and Th2 cells.