Interspecies and interantigenic evaluation of a crossreactive rat idiotype

An interstrain crossreactive idiotype (ID 1), present on rat antibodies to streptococcal group A carbohydrate (SACHO), was examined for both antigen and species specificity. In a test employing a sensitive radioimmunoassay, ID 1 was undetectable in both preimmunization sera and on rat antibodies to poly-glutamic acid⁵⁰-alanine⁵⁰ obtained from animals which subsequently expressed ID 1 on anti-SACHO antibodies. Antigenically distinct from lambda light (L)-chain isotypic determinants, ID 1 was found to require antibody heavy-chain and L-chain interaction for complete expression. The inability to detect ID 1 on anti-SACHO antibodies produced by goats, rabbits, chickens, and nurse sharks suggests the species specificity of ID 1. These and previous observations on idiotypy favor the theory that germline genes are important in coding for rat antibody diversity to SACHO.