ROLE OF RECEPTOR-BINDING IN TOXICITY, IMMUNOGENICITY, AND ADJUVANTICITY OF ESCHERICHIA-COLI HEAT-LABILE ENTEROTOXIN

The role of receptor binding in the toxicity, immunogenicity, and adju vanticity of the heat-labile enterotoxin of Escherichia coli (LT) was examined by comparing native LT and LT(G33D), a E-subunit receptor bin ding mutant, with respect to the ability to bind to galactose and to G R II, toxicity on mouse Y-1 adrenal tumor cells, the ability to stimul ate adenylate cyclase in Caco-2 cells, enterotoxicity in the patent mo use model, and oral immunogenicity and adjuvanticity. In contrast to n ative LT, LT(G33D) was unable to bind to the galactosyl moiety of Seph arose 4B or GM1 but did retain the lectin-like ability to bind to immo bilized galactose on 6% agarose beads. LT(G33D) had no enterotoxicity in the patent mouse model but exhibited residual toxicity on mouse Y-1 adrenal tumor cells and had an ability equivalent to that of native L T to stimulate adenylate cyclase in Caco-2 cells (5,000 versus 6,900 p mol per mg of protein). In addition, LT(G33D) was unable to serve as a n effective oral adjuvant for induction of immunoglobulin G or A direc ted against a coadministered antigen, Furthermore, LT(G33D) elicited n egligible serum and mucosal antibody responses against itself. These d ata indicate that the toxicity, immunogenicity, and oral adjuvanticity of LT are dependent upon binding of the B subunit to ganglioside GM1.