Escherichia coli heat-labile enterotoxin binds to glycosylated proteins with lactose by amino carbonyl reaction

Identifying a stable bulk dmLT adjuvant formulation at a clinically relevant concentration

Double mutant heat-labile toxin (dmLT) is a novel vaccine adjuvant under development with several different vaccine candidates. Studies using existing dmLT adjuvant stocks require significant dilution to achieve a clinically relevant dose. This dilution leads to wastage of the adjuvant. This manuscript describes a limited formulation study to improve the stability of bulk dmLT at a more clinically relevant concentration (20 µg/mL) with minimal changes to the existing bulk dmLT formulation. In vitro methods were used to evaluate dmLT stability after lyophilization and short-term accelerated stability studies. The addition of the excipient polysorbate 80 (PS80) at 0.05 % to the existing dmLT formulation was identified as the lead modification that provided improved stability of the lyophilized dmLT at 20 µg/mL through 4 weeks at 40 °C.

Cholera toxin: A paradigm for multi-functional engagement of cellular mechanisms (Review)

Cholera toxin (Ctx) from Vibrio cholerae and its closely related homologue, heat-labile enterotoxin (Etx) from Escherichia coli have become superb tools for illuminating pathways of cellular trafficking and immune cell function. These bacterial protein toxins should be viewed as conglomerates of highly evolved, multi-functional elements equipped to engage the trafficking and signalling machineries of cells. Ctx and Etx are members of a larger family of A-B toxins of bacterial (and plant) origin that are comprised of structurally and functionally distinct enzymatically active A and receptor-binding B sub-units or domains. Intoxication of mammalian cells by Ctx and Etx involves B pentamer-mediated receptor binding and entry into a vesicular pathway, followed by translocation of the enzymatic A1 domain of the A sub-unit into the target cell cytosol, where covalent modification of intracellular targets leads to activation of adenylate cyclase and a sequence of events culminating in life-threatening diarrhoeal disease. Importantly, Ctx and Etx also have the capacity to induce a wide spectrum of remarkable immunological processes. With respect to the latter, it has been found that these toxins activate signalling pathways that modulate the immune system. This review explores the complexities of the cellular interactions that are engaged by these bacterial protein toxins, and highlights some of the new insights to have recently emerged.

Immune response to a mucosally administered aflatoxin B1 vaccine

In the present study, a mucosal vaccine was used in an effort to elicit serum IgG and intestinal secretory IgA against the mycotoxin aflatoxin B1 (AFB) in chickens. AFB was coupled to carrier proteins (BSA and porcine thyroglobulin) for use as a vaccine and ELISA coating antigen, respectively. Seven-day-old broiler chicks were divided into groups of 10 and immunized with one of four vaccine preparations: 1) AFB-BSA conjugate alone, 2) AFB-BSA linked to the B subunit of the recombinant heat-labile enterotoxin of Escherichia coli (rLT-B), 3) AFB-BSA admixed with rLT-B, or 4) AFB-BSA mixed with cholera toxin (CT). Each vaccine preparation was administered perorally, intrarectally, or intraperitoneally, with a booster immunization given 2 wk later. Sera and feces were collected weekly and assayed using isotype specific ELISA. All three routes of immunization elicited significant serum IgG responses; however, the intraperitoneal route was strongest for all vaccine preparations tested. The serum IgG immune response to the AFB-BSA conjugate was enhanced by co-administration of rLT-B but not by covalent coupling to rLT-B or coadministration with CT. Secretory IgA anti-CT and anti-rLT-B antibodies were detected in fecal supernatants, but no anti-AFB responses could be detected. As all 12 treatment groups produced significant levels of serum IgG anti-AFB, any of these approaches, including oral administration without adjuvant, may afford the chicken some level of protection through simple immuno-interception of free AFB.

The amino acids of Escherichia coli enterotoxin B subunit involved in binding to Bio-Gel A-5m or to the glycoprotein from mouse intestinal epithelial cells

We determined whether Arg13, Met31, and Ser95 of the heat-labile enterotoxin B subunit (LT-B) might be involved in Lt-B binding to oligosaccharides, which did not bind to the B subunit of the cholera toxin (CT-B). Three LT-B mutants, R13H, M31L, and S95A were prepared by substituting three amino acid residues that differ in CT-B. These mutants formed a pentamer and exhibited the same binding ability to the GM1 ganglioside as native LT-B. Although these mutants did not bind to Bio-Gel A-5m, they did bind to the glycoprotein from mouse intestinal cells in the order R13H > M31L > S95A. These data suggest that Ser95, Met31, and Arg13 are important for LT-B binding to Bio-Gel A-5m, and that although Ser95 is also partially responsible for LT-B binding to the glycoprotein, Arg13 has no significant involvement in it.

Characterization by Western blotting of mouse intestinal glycoproteins bound by Escherichia coli heat-labile enterotoxin type I

Escherichia coli heat-labile enterotoxin type I (LT-I)-binding galactoproteins, which were not recognized by cholera toxin, were detected in intestinal epithelial cells of BALB/c mouse by Western blotting. Inhibitory studies using lectins and modifications of sugar chain suggest that LT-I recognizes certain mucin-type sugar chains containing the terminal Galbeta1-3GalNAc sugar sequence in the galactoproteins. The terminal sugar sequence is identical to that of GM1 ganglioside, the well-documented functional receptor for LT-I.