Molecular Immunology, Vol. 21. No. 2, pp. 127-136, 1984 Printed in Great Britain 0161-5X90/84 $3.00 + 0.00 Pergamon Press Ltd zyxwvut Fc-DEPENDENT EFFECTOR FUNCTIONS OF IDIOTYPE-ANTI-IDIOTYPE IMMUNE COM PLEXES E. RAJNAV~~LGYI,* M. RETH,~. F. UHER,* K. MIKL~)s,* J. GERGELY* and K. RAJEWSKY~~ *Department of Immunology, Eijtviis Lorand University, G6d, Hungary; tlnstitute for Genetics, University of Cologne, Cologne, F.R.G. zyxwvutsrqponmlkjihgfedcbaZY (Receiwd 13 July 1983; accepted 13 September 1983) Abstract-Some effector functions of antigen-antibody and antibody-antibody (idiotype-anti-idiotype) complexes were analyzed. As a model system a monoclonal IgM antibody specific for the hapten NP (antibody Bl-8) was reacted either with hapten and hapten-carrier conjugates or with monoclonal anti-idiotope antibodies with specificity for Bl-8 idiotopes. The precipitating, Clq-binding, complement- activating and Fc receptor binding properties of these complexes were compared. Binding of both haptenxarrier conjugates and anti-idiotope antibodies to Bl-8 results in formation of complexes which depending on the Bl-8:ligand ratio precipitate, activate complement, bind Clq and exhibit increased avidity for Fcp and Fey receptors of mouse spleen cells. In both types of complexes cross-linking of IgM molecules is essential for triggering these Fc-dependent functions, and a functional heterogeneity if idiotype-anti-idiotope complexes based on different idiotype-anti-idiotope ratios could also be observed. The functional similarity of Bl-8-hapten-zarrier and Bl-&anti-idiotope complexes suggests that regu- latory functions so far assigned to antigen-antibody complexes could be carried out also by idiotype-anti-idiotope complexes. INTRODUCTION Certain regulatory functions of immune complexes are well established (Theophilopoulos and Dixon, 1979). It is also known that the immune system is able to generate anti-idiotypic antibodies recognizing idio- typic determinants on the variable portion of any given antibody and Jerne (1974) has advanced the hypothesis that idiotype-anti-idiotype interactions represent a major regulatory mechanism in the im- mune system. In accord with this view is a large body of experimental data showing that anti-idiotypic anti- bodies are potent regulators of immune responses [reviewed by Rajewsky and Takemori (1983)]. Even isologous monoclonal anti-idiotope antibodies pro- foundly affect the expression of the corresponding idiotope-bearing antibodies if applied in nanogram to microgram doses (Reth et al., 1981; Kelsoe et al., 1981). What is the primary target of these antibodies? One possibility is that complexes are formed between $Correspondence to this author at: Institute for Genetics, University of Cologne, Weyertal 121, 5000 Kaln 41, F.R.G. §Abbreviations: BSA, bovine serum albumin; cap, 6-amino-caproic acid; DGVB, dextrose gelatin-Verona1 buffer; DTE, dithioerythritol; EA, red blood cells coated with antibodies; EA,, sheep erythrocytes coated with rat IgG; EA,, sheep erythrocytes coated with mice IgM; FCS, fetal calf serum; Fey zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA R, Fc receptor for IgG; Fcp R, Fc receptor for IgM; NIP, (4.hydroxy-5-iodo-3- nitrophenyl) acetyl; NNP, (4-hydroxy-315-dinitrophenyl) acetyl; NP, (4-hvdroxv-3-nitrophenvl) acetvl: PBS. phosphate-buffered saline; PEG’, polyethylene glycolf RFC, rosette-forming cells; SRBC sheep erythrocytes; VBS, veronal-btiffered saline. anti-idiotopes and idiotope-bearing antibodies and that these complexes, depending on size and com- position, exert specific regulatory effector functions. In the present paper we do a first step in approaching this problem by comparing immuno- chemically defined effector functions of antigen- antibody and antibody-antibody (idiotype-anti- idiotope) complexes. We use as a model system a set of monoclonal anti-idiotope antibodies with specificity for idiotopes on the variable portion of a monoclonal IgM, i anti-NP§ antibody, designated Bl-8 (Reth et al., 1978, 1979). Antibody Bl-8 was derived from the primary anti-NP response of C57BL/6 mice and is heteroclytic in that it binds the related haptens NNP-cap and NIP-cap with higher affinity (lo-’ M/L) than the immunising hapten NP- cap (10m6 M/L). Two anti-idiotope antibodies of the IgGl class and CBA origin were selected (antibodies Ac146 and Ac38) and complexes between Bl-8 and these antibodies were compared with complexes of Bl-8 with hapten and hapten-carrier conjugates with respect to precipitating, Clq-binding, complement- activating and FcR binding properties. MATERIALS AND METHODS Immunoglobulins and their fragments The anti-NP hybrid cell antibodies Bl-8 (p, Al), BI-48 (‘J1, 11) and S43 (y2a, i 1) were isolated from the C57BL/6 response by the cell fusion technique [for details see Reth et al. (1977, 1978)]. They were purified by adsorption to NP-BSA coupled to Se- pharose 4B (Pharmacia Fine Chemicals, Uppsala, 127