Surface immunoglobulin on rabbit lymphoid cells. IV. Ultrastructural labelling of A and B group allotypic determinants.

Equal numbers of rabbit peripheral blood lymphocytes (PBLs) label for either a- or b-group immunoglobulin allotypes using a modification of the mixed antiglobulin reaction of Coombs adapted for electron microscopy. This technique which employs immunoferritin markers is consistently more sensitive than other methods used for labelling surface Ig on lymphocytes. Although approximately 75 per cent of PBLs label for either a- or b-group allotypes, the number of immunoferritin grains on the cell surface after labelling for b group allotypes is nearly twice as great as that observed after labelling for a group allotypes. We conclude that essentially all Ig-bearing blood lymphocytes of the rabbit express both heavy chains (a allotypes) and light chains (b allotypes) on their surface membranes, but that light chain allotypic determinants are more accessible or exposed than the heavy chain (Fd) allotypic determinants.