Production of antiidiotypic antibodies in the rat: in vitro characterization of specificity and correlation with in vivo specific suppression of cardiac allograft immune reaction across major histocompatibility complex.

We studied the effect of antiantidonor major histocompatibility complex antibodies (antiidiotypic antibodies) in vivo on ACI cardiac allograft survival in Lewis rats and correlated the results with in vitro mixed lymphocyte culture. Lewis anti-ACI hyperimmune sera (Ab1) were obtained from animals that have rejected successive ACI skin grafts. Purified immunoglobulin (Ig) G and IgM fractions were obtained from the sera. These putative "idiotypic antibodies" (IgG fractions) were used to immunize groups of five naive Lewis rats. Purified Ig (0.5 mg) was mixed with 0.5 ml incomplete Freund's adjuvant and injected intraperitoneally -15, -7, and -3 days before and at the time of ACI cardiac allografting. The median allograft survival time was 11.2 +/- 0.7 days in animals treated with Ab1 compared with 6.4 +/- 0.5 days in untreated control rats (p less than 0.001). Use of IgM with adjuvant did not prolong graft survival. Purified IgG obtained from sera collected before transplantation was tested for antiidiotypic antibodies with the complement-mediated cytotoxicity assay. For this, serial dilutions of the hyperimmune serum were tested for cytotoxicity against ACI lymphocyte in the presence of Ig from sera collected after immunization with Ab1. Blocking was demonstrated by sera and IgG obtained from Lewis rats that received anti-ACI IgG (Ab1) with adjuvant. The blocking activity of purified IgG (Ab2) was strain specific because it did not block the reaction of Lewis hyperimmune sera against third-party Wistar-Furth rats. Thoracic duct lymphocytes from immunized recipients showed no blastogenic responses when tested in in mixed lymphocyte culture for reactivities against splenocytes from ACI rats. The finding that Lewis rats treated with Ig from sera containing anti-ACI antibodies exhibit impaired anti-ACI T- and B-cell reactivity and prolong allograft survival suggests that pretreatment of recipients with idiotypic antibodies leads to development of antiidiotypic antibodies that modulate alloreactivity suppressing allograft rejection.