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.