Structural studies of induced antibodies with defined idiotypic specificities. IV. The heavy chains of anti-streptococcal group A carbohydrate antibodies from Sprague-Dawley rats carrying a cross-reacting idiotype.

The heavy (H) chains of three anti-streptococcal group A carbohydrate antibodies (anti-SACHO) of restricted heterogeneity, elicited in inbred Sprague-Dawley rats, were subjected to 40 cycles of automated Edman degradation. All three antibody H-chain preparations had an identical amino acid sequence and were classified as a variant of the VHIII subgroup of immunoglobulin H chains. A comparison of the H-chain sequence of these antibodies with that of pooled rat gamma chains suggests that a very minor population of H chains (closely related to the VHIII subgroup) has been 'recruited' as a consequence of this immunization. This observation further supports the notion that 'framework' and 'specificity' or 'hypervariable regions' are closely linked.