CHEMICAL DENATURATION OF OVALBUMIN ABROGATES THE INDUCTION OF ORAL TOLERANCE OF SPECIFIC IGG ANTIBODY AND DTH RESPONSES IN MICE

We have examined the effects of ingestion of chemically denatured oval bumin (OVA) in mice. Both 8 M urea-denatured OVA (UD-OVA) and carboxym ethylated UD-OVA (CM-OVA) were purified by gel filtration. Specific Ig G antibody and systemic delayed-type hypersensitivity (DTH) responses to OVA were not suppressed by CM-OVA fed prior to or after immunizatio n with OVA in complete Freund's adjuvant (CFA). When CM-OVA was used i nstead of OVA for immunization, serum IgG and DTH responses to CM-OVA were or-ally tolerized by OVA, but not by UD-OVA or CM-OVA. Studies of antigen uptake in mice using sandwich ELISA tests showed that OVA, bu t not CM-OVA, was absorbed after antigen ingestion. In vitro studies f urther demonstrated that CM-OVA was digested much more rapidly than OV A. Moreover, studies using bovine serum albumin (BSA) demonstrated tha t both IgG and DTH responses to BSA were orally tolerant to BSA, but n ot to denatured BSA. Finally, studies using human gamma-globulin (HGG) , a well-known tolerogen, also found that the IgG antibody response to HGG was not orally tolerized by denatured HGG. These results suggest that complete denaturation of globular proteins may affect their proce ssing and absorption in the gut and thus abrogates oral tolerance indu ction.