THE POLYMORPHIC HUMAN TLX-B CD46/MCP SYSTEM AND ITS IMPLICATIONS IN TRANSPLANTATION AND REPRODUCTION/

TLX antigens have been found on most peripheral blood cells, trophobla sts, seminal vesicle cells and sperms. These antigens seem to be assoc iated with the membrane cofactor protein (MCP) and the CD46 antigen. A lloantibodies to TLX antigens with Fc tau RII-blocking features were o btained by transfusion of leucocytes or platelets. Preliminary populat ion studies revealed that alloantibodies to TLX/CD46/MCP recognize fou r overlapping specificities. The terminology TLX-B was introduced with specificities TLX-B1, B2, B3, B4 and frequencies obtained in the popu lation were: 38%, 46%, 42% and 26%, respectively. Family studies showe d an independent segregation of the TLX and HLA alleles. At the cellul ar protein on trophoblast, the alloantibody detected a glycoprotein of 66-67 kDa molecular mass, which may correspond to the a chain of the TLX/CD46/MCP isotypes. A direct association of the alloantibody with F c tau RII could be excluded thus its FcR blocking feature is probably based on an indirect functional effect. After transfusion and in pregn ancy the induction of TLX alloantibody production depended on the mism atching in the TLX/CD46/MCP phenotypes. Probable associations were rev ealed in the case of recurrent habitual abortion between the lack of F c tau R blocking antibody production and the marched TLX specificities of the couples. After transfusion, TLX alloantibody production with F c tau R and MLR blocking function was induced only when the recipient was lacking the TLX specificities expressed on the donor cells. Suppre ssion of MLR was found only when TLX specificity in sera corresponded to the TLX specificity of the effector cell. The immunopathological im portance of these findings in transplantation and reproductive medicin e has yet to be clarified.