The murine homologue of the T lymphocyte CD2 antigen: molecular cloning, chromosome assignment and cell surface expression.

The human T lymphocyte antigen CD2 (T11, sheep erythrocyte receptor) is expressed on all peripheral T cells and all but the most immature thymocytes. Experiments with monoclonal antibodies against CD2 suggest that CD2 is the cell surface receptor for a natural ligand involved in T cell proliferation. Clarification of the functional role of CD2 would be facilitated by the identification of CD2 in the mouse. However, antibodies that recognize the murine homologue have not been described. An alternative approach to the identification of the murine homologue was to use cross-species DNA hybridization, employing human CD2 cDNA as a probe. Clones encoding the murine homologue were isolated from a murine T helper cell cDNA library. The murine cDNA sequence encoded a predicted mature polypeptide of 322 amino acids that showed 54% identity with the predicted human sequence. As with the human polypeptide, the cytoplasmic domain was large, and rich in proline and basic residues. CD2 mRNA was expressed in murine thymus and spleen, and in the T cell line EL4. The murine CD2 gene was assigned to chromosome 3 by Southern blot analysis of mouse-hamster somatic cell hybrids. A rabbit antiserum raised against purified human CD2, precipitated from surface-labeled mouse thymocytes a glycoprotein of Mr 55,000-66,000 which decreased to Mr 35,000 on digestion with endo-beta-acetylglucosaminidase F. These sizes are consistent with those predicted for the murine CD2 antigen from the cDNA sequence.