Structure of chicken 7S immunoglobulin allotypes: Further studies on localization to Fab and Fc fragments

Papain-derived fragments (Fab and Fc) were used to localize previously uncharacterized chicken 7S immunoglobulin (Ig§) allotypic specificities (G-1.7, G-1.8, G-1.9, G-1.10, and G-1.12). Based on the molar amounts of Fab and Fc preparations relative to undigested 7S Ig to inhibit 50% of binding of 125I-7S Ig with homologous alloantiserum, the G-1 allotypes, including some previously reported (G-1.1, G-1.2, G-1.3 and G-1.5), were grouped according to the extent of their modification induced by digestion with papain. The Fab determinants G-1.1 and G-1.12 were considered unmodified and Fab determinant G-1.2 was slightly modified. Although found in an Fab preparation, G-1.8 was greatly modified. Similarly, G-1.3 and G-1.5 were greatly modified, but were found in very low concentrations in Fc preparations. The G-1.10 also was greatly modified but it was found in low concentrations in both Fab and Fc preparations. The G-1.7 and G-1.9 specificities were undetectable (completely destroyed) after papain digestion. No G-1 allotype has been found with high activity in Fc preparations. All allotypes greatly modified or completely destroyed by papain digestion were considered to be papain-sensitive. Most alleles had both Fab and papain-sensitive determinants. A new 7S Ig allotype, G-1.14, was associated with the G-1 a , G-1 b , G-1 c , G-1 f and G-1 g alleles and did not result in the formation of new alleles in inbred chickens homozygous for the allotype loci.