A MONOCLONAL-ANTIBODY (A6) RECOGNIZING A UNIQUE EPITOPE RESTRICTED TO CD45RO AND RB ISOFORMS OF THE LEUKOCYTE COMMON ANTIGEN FAMILY IDENTIFIES FUNCTIONAL T-CELL SUBSETS

The mAb A6 was produced by immunization of mice with human PHA-stimulated PBMC. Immunoprecipitation studies and staining of cell lines transfected with individual leukocyte common antigen (LCA) isoforms showed that A6 recognizes a unique epitope strongly expressed on the lower MW isoform (p180) of LCA, but also weakly expressed on the p190 isoform coded by exon B and the p205 coded by exons A and B. The epitope recognized by A6 was carbohydrate-dependent in that it was neuraminidase-sensitive, but trypsin-resistant. A6 stained most TCR-alpha beta(+) cells with differential intensities, subdividing them into a bright and dim population, and strongly stained all TCR-gamma delta(+) cells. A6 did not stain CD19(+) B cells nor CD56(+) NK cells. Anti-CD45 mAb such as UCHL1 recognizing CD45RO have been used to define memory T cells. Depletion of PBMC subsets with A6 or UCHL1 mAb dramatically decreased proliferative responses to the recall antigens anti-CD3 mAb and alloantigen and enhanced their responses to PHA. A6, unlike UCHL1, also depleted alloreactive T cells that affect primary and secondary MLC and CML. Thus, A6 was shown to recognize the lower MW isoforms of LCA which are expressed on functional T cell subsets including memory, activated, and alloreactive T cells. (C) 1994 Academic Press, Inc.