ALLELE-SPECIFIC EXPRESSION OF THE MOUSE B-CELL SURFACE PROTEIN CD72 ON T-CELLS

CD72 is a 45 000 M(r) mouse B-cell surface glycoprotein involved in B- cell proliferation and differentiation. Expression of mouse CD72 is th ought to be restricted to the B-cell lineage. We recently demonstrated that the monoclonal antibodies K10.6 and B9.689, previously defined a s recognizing the mouse lymphocyte alloantigens Ly-19.2 and Ly-32.2, r espectively, recognize specific alleles of CD72. Early studies using a ntibody-mediated cytotoxicity assays demonstrated that K10.6 and B9.68 9 react with B cells, several T-cell lines, and a subset of peripheral T cells. These findings led us to consider the possibility that CD72 might also be expressed on a subset of T cells. In this report we demo nstrate that CD72 is constitutively expressed on a fraction of periphe ral T cells isolated from strains of mice expressing the CD72(b) allel e, but not the CD72(a) or CD72(c) alleles. Three days after activating T cells with concanavalin A or plate-bound CD3-specific mAb, CD72 is expressed on a larger fraction of peripheral T cells as well as a frac tion of thymocytes from mouse strains expressing the CD72(b) allele. C D72 is expressed on both the CD4(+) and CD8(+) thymocyte and periphera l T-cell subsets. No CD72 expression is detected on activated thymocyt es or peripheral T cells from mouse strains expressing the CD72(a) or CD72(c) alleles. Expression of CD72(b) on peripheral T cells was confi rmed by northern blot analysis demonstrating CD72 mRNA expression. The se results demonstrate that CD72 expression is not restricted to B lin eage cells in mouse strains expressing the CD72(b) allele; instead, a population of T lineage cells in these mice also expresses CD72.