Expression of alternatively spliced exons of CD45 in peripheral T-cell lymphomas and its correlation to the expression of adhesion molecules

The expression of CD45RO, CD45RA, and CD45RB (n = 35) was examined in paraf fin sections from 35 T-cell lymphomas. A protocol including microwave irrad iation for the demasking of antigens was used for the detection of RA and R E. CD45 RC was studied in the 15 lymphomas for which frozen material was av ailable. In addition to the CD45 isoforms, the expression of adhesion molec ules CD44, CD38, LFA-1, CD54 (ICAM-1), CD62L (L-selectin), and O-acetyl GD3 was studied, most of them requiring staining from frozen sections. The exp ression of alternatively spliced exons of CD45 was, with one exception, com patible with a memory type of T lymphocyte, i.e., expressing RO and RE but not RA and RC. RE showed some heterogenicity of staining, especially when p leomorphic T-cell lymphomas with medium-sized cells and small/medium sized cells were studied. It had been suggested earlier that the expression of al ternatively spliced exons of CD45 is solely dependent on the number of CD45 expressed, and that the expression of these will follow the hierarchy RE > RA = RC. The results of this study are compatible with this model. The lac k of RA in lymphomas is in some contrast to earlier findings concerning T-c ell leukemias. Possible reasons for this divergence are discussed. The expr ession of adhesion molecules was also compatible with a memory phenotype. C D44, CD38, LFA 1, and ICAM-1 were widely expressed, whereas CD62L (L-select in) was not. Interestingly, CD62 was not expressed in several nodal sites, although the lymphomas in question otherwise conformed to a memory phenotyp e. The expression of adhesion molecules therefore correlated well with the expression of alternatively spliced exons of CD45. In individual cases, how ever, some discrepancies in this respect arose, i.e., cells expressing mole cules associated both with a memory phenotype and a naive phenotype. The ly mphomas expressed O-acetyl GD3 ganglioside only in a few cases, contrary to the pattern seen in normal RO-positive: cells in which >80% of the cells s tain positive for 27A.