Blocking of certain antigenic sites in the F(ab) region by combination of univalent fragments of Rh antibodies with red cell antigens.

Evidence was obtained in the present study substantiating the fact that divalent Rh antibodies are bound to antigenic sites on the red cells through only one of the two combining sites. Univalent F(ab) fragments bound to the red cell lacked such free-combining sites and showed a blockage of various idiotypic-like antigens which were readily detected when divalent antibodies or divalent fragments were used. The univalent fragments contained the antigens because they completely inhibited the divalent system. These antigens were detected with idiotypic antisera made to a variety of monoclonal Ig through the use of certain very heterogeneous anti-Rh sera. As is the case with many other idiotypic systems, combination with antigen which blocked the antibody-combining site eliminated the reactivity. Advantage was taken of these differences between divalent and univalent antibodies to determine antigens in the F(ab) portion of Rh antibodies which are or are not blocked by such combination with the red cell. A variety of subclass and genetic markers found in the constant regions of the F(ab) units were not affected. However, in addition to the idiotype-related antigens a series of V region markers, particularly those determining various V region subgroups, were not detected after combination.