Recognition and genetic control of helper determinants for cell surface antigen Thy–1

Abstract

THE hapten-carrier effect in immune responses demonstrates that one antigenic determinant can strongly modulate the antibody response to a second determinant if the two exist in physical association. This phenomenon, in more general form termed associative recognition¹, has been analysed with soluble antigens and reveals collaboration between carrier-directed, helper T cells and hapten-directed, antibody-producing B cells. In contrast to soluble antigens, antibody responses to surface antigens of nucleated cells are poorly understood and although collaboration among T and B cells is indicated in several studies^2–4 the antigenic sites recognised by these T cells and the extent of associative recognition among the different antigenic determinants on cell membranes is not known. Thus, it is not clear whether the determinants recognised by T and B cells are controlled by a single gene and are joined covalently or if the two determinants are controlled by independent genes and are only loosely associated or even unassociated on the cell surface. This knowledge would help determine the character and extent of molecular interactions on the surface of nucleated cells as well as principles of immunogenicity of antigens expressed on cell membranes. This report extends previous findings^1,5 and describes a new experimental approach to study, in primary responses the role of alloantigens in the immunogenicity of Thy-1 through the use of closely related donor-recipient strains and an assay for antibody plaque-forming cells (PFC). The results are consistent with the notion that in primary immune responses Thy-1 is ‘helpless’ but that in appropriate donor strains, help may be supplied by other alloantigens controlled elsewhere in the donor genome.