Polyclonal anti-idiotypic antibodies exhibit antigenic mimicry of limited type 1 fimbrial proteins of Escherichia coli.

Polyclonal anti-idiotypic antibodies (anti-Ids)(fim) developed against idiotypes on antibodies (Ab-1s) that specifically bind structural, organelle fimbrial proteins of Escherichia coli were able to modulate immune function in anti-Id(fim)-immunized mice. Proliferation or suppression of splenic lymphoid cell responses by polyclonal anti-Ids in tissue culture appeared to be dose dependent. Anti-Ids were able to induce a dose-dependent T-cell-mediated immunity specific for type 1 fimbrial antigen(s) in immunized animals when assessed in vitro, but they failed to elicit in vivo positive ear-swelling skin reactions. Anti-Ids were unable to induce protective immunity against an in vivo infectious challenge with E. coli in anti-Id-immunized adult animals, but they stimulated a specific, secondary antibody response in anti-Id-challenged mice. Anti-Ids stimulated the development of anti-anti-Ids (Ab-3s) specifically binding a fimbrial antigen(s) and revealed the presence of antibody idiotypes binding E. coli adhesin proteins in the 27- to 29-kilodalton range. Results suggest discrete, but subtle, immunomodulatory effects of the anti-Ids and potential vaccinoid properties capable of stimulating a specific humoral and cellular response in vivo.