Isolation and characterization of monoclonal antibodies directed against murine FRP-1/CD98/4F2 heavy chain: Murine FRP-1 is an alloantigen and amino acid change at 129 (Pt <--> R) is related to the alloantigenicity

Nineteen mAb directed against murine fusion regulatory protein-1 (mFRP-1)/4 F2/CD98 were isolated and their biological properties were analysed. Intrig uingly, mFRP-1 was found to be an alloantigen, namely, FRP-1.1 (DBA/2 and C BA mice type) and FRP-1.2 (BALB/c, C57BL/6 and C3H/He mice type). The nucle otide sequences of FRP-1.1 and FRP-1.2 were determined, demonstrating that amino acid change at 129 (P<-- -->R) is related to the alloantigenicity. mF RP-1 is expressed on thymocytes, on spleen cells, on peripheral lymphocytes and on blood monocytes, suggesting that the physiological role in vivo of murine FRP-I is different from that of human FRP-1. The biological activiti es of antimFRP-1 mAbs showed by the present study are: (i) enhancement of N ew-castle disease virus-induced cell fusion; (ii) suppression of HIVgp 160- mediated cell fusion; and (iii) induction of aggregation and multinucleated giant cells of monocytes/macrophages.