Interdependent membrane mobility of human MHC coded antigens detected by monoclonal antibodies to various epitopes on class I and II molecules

Binding of monoclonal antibodies (MAB) to human MHC coded class I antigens, w6.32HL or 61D2, specifically leads to clustering of these antigens and their assembly at one polar site on a cell, whereby these class I antigens tow class II-antigens with them into the polar cap revealing preexisting or arising molecular complexes in the membrane of the living cell. These class II antigens included DR (seen by MAB 2MC3, L203, L227, I-LR2, 109d6, SFR-3) and DQ (seen by Genox 3.53 and IVD12). In analogous cocapping experiments employing MAB to various class II antigens, interdependent surface mobility (bidirectional cocapping) could be demonstrated between DRw52 (MT2, seen by I-LR2) and DQw3 (MB3, seen by IVD12) as well as between DRw53 (MT3, seen by 109d6) and DQw3. There was incomplete interdependence between DRw52 or DRw53, respectively, and other DR antigens (seen by L227). These latter antigens were independent from DQ (seen by Genox 3.53 or IVD12). Analyzing pairs of monoclonal antibodies with various specificities to determinants on class I or II molecules a frequent finding was unidirectional cocapping: here a first antibody cocapped epitopes seen by a second, but this antibody did not cocap epitopes seen by the first. We conclude that epitopes are irregularly distributed on MHC coded molecules or on complexes of these molecules.