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, trophoblasts, seminal vesicle cells and sperms. These antigens seem to be associated with the membrane cofactor protein (MCP) and the CD46 antigen. Alloantibodies to TLX antigens with Fc tau RII-blocking features were obtained by transfusion of leucocytes or platelets. Preliminary population studies revealed that alloantibodies to TLX/CD46/MCP recognize four overlapping specificities. The terminology TLX-B was introduced with specificities TLX-B1, B2, B3, B4 and frequencies obtained in the population were: 38%, 46%, 42% and 26%, respectively. Family studies showed an independent segregation of the TLX and HLA alleles. At the cellular protein on trophoblast, the alloantibody detected a glycoprotein of 66-67 kDa molecular mass, which may correspond to the alpha chain of the TLX/CD46/MCP isotypes. A direct association of the alloantibody with Fc tau RII could be excluded thus its FcR blocking feature is probably based on an indirect functional effect. After transfusion and in pregnancy the induction of TLX alloantibody production depended on the mismatching in the TLX/CD46/MCP phenotypes. Probable associations were revealed in the case of recurrent habitual abortion between the lack of Fc tau R blocking antibody production and the matched TLX specificities of the couples. After transfusion, TLX alloantibody production with Fc tau R and MLR blocking function was induced only when the recipient was lacking the TLX specificities expressed on the donor cells. Suppression of MLR was found only when TLX specificity in sera corresponded to the TLX specificity of the effector cell. The immunopathological importance of these findings in transplantation and reproductive medicine has yet to be clarified.