Cross-reactive idiotype family observed in the phthalate-specific B cell repertoire of adult BALB/c mice: Diversity of IgM compared with IgG monoclonal anti-phthalate antibodies

A highly conserved clonotype has been identified within the repertoire of B cells specific for the negatively charged hapten phthalate. The prototype of this phthalate-specific clonotype is a primary-response hybridoma (2E9) that produces a μ,κ anti-phthalate antibody. The 2E9 monoclonal antibody was found to share idiotypic determinants with several other independently-derived μ,κ and γ₁,κ anti-phthalate monoclonal antibodies and with a significant proportion of conventional anti-phthalate antibodies derived from all of the BALB/c mice immunized with phthalate-keyhole limpet hemocyanin. Competitive RIA analysis of the 2E9 idiotypic relatedness between primary and secondary response antibodies was consistent with the hypothesis that the primary response μ,κ antibodies represent a conserved germ-like product, whereas the secondary response to γ₁,κ antibodies reflects somatic variants of the 2E9 clonotype. Further analysis with a site-specific anti-idiotype reagent suggests that the idiotypic differences between μ,κ and γ₁,κ monoclonal antibodies occur at positions outside of the combining site. Fine specificity analysis of the monoclonal antibodies expressing the 2E9 cross-reactive idiotype (CRI) also supports this hypothesis. Seven to 35% of the anti-phthalate antibodies after a single immunization with phthalate-KLH and 1 to 10% of the antibodies after a second immunization express the 2E9 CRI. The 2E9 CRI was also found in several other strains of mice, and its expression was associated exclusively with anti-phthalate antibodies.