Structural and genetic studies on chicken 7S immunoglobulin allotypes. I. Detection of four heavy chain specificities with a new radioimmunoassay.

A method was developed for the detection of allotypes on intact, radiolabeled 7S immunoglobulin (Ig) which does not involve insolubilized alloantisera. Binding of dinitrophenylated anti-allotype (DAA) antiserum with radiolabeled alloantigen was demonstrated by the addition of rabbit anti-dinitrophenyl antiserum followed by precipitation of complexes with sheep anti-rabbit gamma-globulin antiserum. Dinitrophenylation of alloantiserum up to 8.5 hr had no effect on antibody titer or avidity. Binding inhibition assays with the DAA method detected allotypes on 2 to 5 ng of 7S Ig. Four specificities were detected on 7S Ig heavy (H) chains by binding inhibition with the DAA assay. Specificities CS-1.1 and CS-1.2, located in the Fab fragment, were detected at 3- to 5-fold lower concentrations of reassociated H and light (L) chains than on the isolated H chains. On the basis of regression coefficients calculated from binding inhibition curves, the avidity of isolated H chains was significantly increased following reassociation with L chains, indicating that the conformation of CS-1.1 and CS-1.2 determinants depends in part on H and L chain interactions. In contrast, reassociation of H and L chains did not significantly increase H chain inhibitory activity or avidity for specificities CS-1.3 and CS-1.4.