Clonotypes of anti-phosphocholine antibodies induced with Proteus morganii (Potter). I. Structural and idiotypic similarities in a diverse repertoire.

The PC-specific response to Proteus morganii strain Potter, a mouse intestinal isolate, was examined in mice by isoelectric focusing, fine specificity, light (L) chain, and idiotype analyses. Unlike other PC antigens, this antigen reacts with only 1 of the PC-BMP, McPC 603. Although extracts of both the Potter strain and a prototype ATCC strain contain substantial amounts of choline, only extracts of the Potter strain inhibit M603 binding to PC-bovine γ-globulin. Additionally, only the Potter strain is capable of eliciting a good PC-specific response in BALB/c mice. As determined by IEF analysis of individual sera, the PC response of BALB/c to this antigen is considerably more heterogenous than the response to PC-KLH. Individual samples often contained complex banding patterns, and most mice had unique spectrotypes. However, L chain IEF of purified antibodies revealed a single predominant L chain, and this co-focussed with the L chain of M603. The fine specificity of 1 PC antibody to P. morganii most resembled that of M603. Surprisingly, idiotype analysis detected no IdI-M603 but only very low levels of IdI-T15 and IdI-M511. Therefore, an anti-idiotypic antiserum was prepared to PC-antibodies induced with P. morganii (Potter). This antiserum, anti-IdX-M603, reacts with antibodies in each Proteus immune mouse, cross-reacts with M603, but does not bind other PC-BMP, other classes of myeloma proteins, normal sera, or sera immune to irrelevant antigens. The binding of this antiserum is completely PC-inhibitable. Thus, P. morganii stimulates a heterogenous family of antibodies that are related to, but not identical with, the PC-BMP, M603, and that share L chains and a binding site idiotype.