Antigen‐independent, IgM‐induced antibody responses: requirement for “recurrent” idiotypes

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Abstract
Anti‐idiotypic antibodies (a‐Id) were produced in syngeneic mice against two monoclonal IgM antibodies of BALB/c origin, TNP.11 and SP/603. In plaque inhibition tests, using IgM‐secreting hybridoma cells and anti‐idiotypic antibodies, these two IgM proteins, as well as the anti‐TNP myeloma protein MOPC 460 (IgA) were found to carry non‐cross‐reactive idiotypes. Analysis of the anti‐trinitrophenyl (TNP) plaque‐forming cells (PFC) in BALB/c mice, either normal or immunized with TNP‐horse red blood cells, revealed that in addition to the MOPC 460 Id, also the SP/603 Id is recurrent and expressed by a fraction of the anti‐TNP antibody‐secreting cells in all individuals tested. In contrast, the TNP.11 Id could not be detected in any BALB/c mouse studied. TNP.11 and SP/603 antibodies were then characterized by their ability to induce an antigen‐independent anti‐TNP response in normal BALB/c mice. While TNP.11 was found to be inactive, the same titers of SP/603 IgM induced antigen‐specific PFC all of which expressed the SPi603 Id, and increased titers of circulating IgM molecules carrying the same Id, suggesting that “recurrent” but not “nonrecurrent” Id are competent in this respect. A fraction of these SP/603‐induced, SP/603‐positive anti‐TNP antibodies also carried MOPC 460 Id, suggesting expression on the same molecule of idiotypic determinants found on independent non‐cross‐reactive “recurrent” idiotypes.