Mouse Alloantigen Ly10 Is Identical to Murine Fusion Regulatory Protein-1 (mFRP-1)/4F2/CD98: Aberrant Expression of mFRP-1/Ly10 Allotypes in Cells Derived from CDF1 Mice Due to the Gene Deletion

Murine FRP-1 (mFRP-1) and Ly10 antigens are alloantigens. Anti-Ly10.1, monoclonal antibody (mAb) reacts to HeLa cells stably expressing mFRP-1.1 (HeLa cells/mFRP-1.1), but does not react to HeLa cells/mFRP-1.2. On the other hand, anti-Ly10.2 mAb reacts to HeLa/mFRP-1.2 cells, but does not react to HeLa cells/mFRP-1.1. These findings indicate that Ly10.1 and Ly10.2 antigens are identical to the heavy chains of mFRP-1.1 and mFRP-1.2 molecules, respectively. Thymocytes and fibroblast cells obtained from CDF1 and BDF1 mice showed reactivity to both anti-Ly10.1 and anti-Ly10.2/FRP-2 antibodies, indicating that mFRP-1/Ly10 alloantigens are codominantly expressed in the F1 mice. Intriguingly, IMC carcinoma cells, derived from CDF1 mice, express mFRP-1.2, but do not express mFRP-1.1. Surprisingly, DBT cells, derived from CDF1 mice, consist of two different cell populations: one expresses both mFRP-1.1 and mFRP-1.2 antigens and the other expresses only mFRP-1.1 antigen. Consequently, we tried to isolate cloned DBT cell lines by limiting dilution. Finally, six cloned DBT cell lines were obtained, and three clones of these cloned DBT cells expressed both mFRP-1.1 and mFRP-1.2, and another three clones of these cloned DBT cells expressed both mFRP-1.1 and mFRP-1.2, and another three clones including clone 5 cells expressed only mFRP-1.1 antigen. No induction of mFRP-1.2/Ly10.2 by 5-azacytidine and sodiumn-butyrate could be detected in DBT clone 5 cells. Neither mFRP-1.2 mRNA nor the genomic cDNA clone encoding mFRP-1.2 could be detected in DBT clone 5 cells, nor could the genomic cDNA encoding mFRP-1.1 be detected in IMC cells, indicating that aberrant expression of mFRP-1/Ly10 allotypes in CDF1 mice-derived cells is due to the gene deletion.