Structural and genetic studies on chicken 7S immunoglobulin allotypes. IV. The presence of an unexpected chicken immunoglobulin heavy chain allotype: subclass or pseudoallele?

Low concentrations of allotypic specificity CS-1.1 were detected in the sera of two inbred chicken lines [University of California, Davis (UCD) 7 and Regional Poultry Research Laboratory 15I4] previously reported to lack this specificity. The CS-1.1 alloantigen in 15I4 chickens has the same specificity as the major allotype in a line of chickens (UCD 2) in which it was initially defined. In 15I4 chickens, CS-1.1 allotype is present on a population of molecules distinct from those which carry the major allotype; thus a second 7S Ig H chain locus, CS-2, is proposed. The concentration of CS-1.1-bearing molecules determined by two different methods was 7 microgram/ml and 230 microgram/ml in 15I4, whereas UCD 2 chickens had 4 mg/ml of CS-1.1 molecules. The levels of CS-1.1 inhibitory activity in 15I4 birds remained relatively constant over a 30-day period. The presence of two 7S Ig populations in 15I4 chickens may be interpreted as evidence either for 7S Ig subclasses with shared allotypes or for a pseudoallelic organization of genes controlling expression of 7S Ig H chains. The results were consistent with the presence of redundant C region genes, differing in allotypes, whose expression is under the control of an as yet undefined regulatory mechanism.