A novel method for radiolabeling antigen-binding receptors of lymphocytes

A unique polypeptide on avian antigen-specific suppressor T-cell radioiodinated in situ by antigen-lactoperoxidase conjugates

Antigen-specific receptors of B- or T-cells were selectively radiolabeled among the spleen cells from either human gammaglobulin immunized normal or bursectomized agammaglobulinemic chickens. Selective in situ radioiodination was accomplished by employing lactoperoxidase (LPO) covalently linked to antigen (Ag). Ag-specific receptors on B- or T-cells were allowed to bind Ag-LPO conjugates via the Ag portion of the conjugates and then to be selectively catalyzed for iodination by the LPO portion of the bound Ag-LPO conjugates. Radioiodinated cells were either processed for autoradiography to detect Ag-binding cells directly under the microscope or solubilized with detergents for protein analysis with two-dimensional (2-D) gel electrophoresis. On a cellular level, Ag-binding B- and T-cells were selectively radiolabeled and clearly visualized via autoradiography. On a molecular level, selectively radiolabeled Ag-specific membrane immunoglobulin of B-cells was demonstrated on 2-D gel autoradiographs. Furthermore, a unique polypeptide of Ag-specific T-cells with a reduced apparent mol. wt of 27 K and an apparent pI of 5.5-5.7 was demonstrated on 2-D gel autoradiograms. The 27 K molecule appears to be a T-cell receptor component itself, or a closely associated molecule.

Disulfide linkages between antigen-binding receptors on chicken B-lymphocytes

Membrane immunoglobulin receptors on chicken B-cells have been shown to display a heterogeneity with respect to interchain disulfide linkages. One fraction of the surface Ig (sIg) appears to display the traditional H2-L2 linkage. We also present evidence that this Ig is covalently bound via a disulfide linkage to actin. In this instance, the isolated Ig heavy chain, after reduction, has a mol. wt of 80 K. Perhaps more significantly, we show that another fraction of the sIg exists in a highly aggregated from that is stabilized by disulfide linkages. In contrast to the sIg found in the H2-L2 configuration, there is no evidence of actin within the aggregates and the sIg heavy chains isolated from these aggregates display a slightly faster mobility on SDS-PAGE under reducing conditions, running at about 77K. Furthermore, it appears that the Ig within the large aggregates may have a higher avidity with respect to antigen binding, and so this Ig structure may be the more relevant to antigen-induced receptor-mediated signaling in the B-cell.