Distribution of an Idiotype in Inbred Iv[ice

Idiotypic determinants are present on myeloma proteins (1) and on induced antibodies (2, 3), where they are characterized by their association with antibody of a given specificity. Shared determinants are ordinarily not detectable in nonspecific IgG, 1 in preimmune serum, nor in antibodies of other specificities from the same animal. As would be predicted, idiotypic determinants are localized in the Fab fragment of immunoglobulin molecules (6). In many antibodies the region of the active site appears to be an important idiotypic determinant, as shown by the capacity of specific haptens to inhibit the reaction with anti-idiotypic antibody (7-10).2 Complete blocking by haptens is generally not observed, which suggests the presence of additional idiotypic determinants on the Fab fragment. This is supported by the capacity of Fab fragments from some, although not all, immunoglobulins to form specific precipitates with their anti-idiotypic antibodies (11); this property would require antigenic multivalence. Mice of an inbred strain are frequently observed to produce antibodies of a given specificity with shared idiotype. Intrastrain cross-reactions have been observed among the anti-phosphorylcholine (anti-PC) 3 antibodies of different BALB/c mice (12, 13), the anti-p-azobenzoate antibodies of A/J mice (14), A/J anti-p-azophenylarsonate (anti-At) antibodies (14), BALB/c anti-p-azobenzoate antibodies (14), BALB/c anti-oe,l,3-dextran antibodies (15), and A/J antistreptococcal carbohydrate antibodies (16). In contrast, intrastrain idiotypic cross-reactions among the anti-p-