J. Scott Moncrief

Fragilysin, the enterotoxin from Bacteroides fragilis, enhances the serum antibody response to antigen co-administered by the intranasal route

Fragilysin, an extracellular zinc metalloprotease produced by enterotoxigenic strains of the anaerobic bacterium Bacteroides fragilis, disrupts the paracellular barrier by cleavage of the intercellular proteins between epithelial cells resulting in fluid secretion. Intranasal immunization of mice with fragilysin and co-administered ovalbumin (Ova) resulted in an Ova-specific serum IgG response that was over 18000-fold higher than Ova alone, as well as detectable levels of serum IgA. Serum IgG titers were comparable with those seen when whole cholera toxin was used as the adjuvant, although the responses obtained with fragilysin showed more variability between mice. Metalloproteases to which fragilysin is structurally related were ineffective as mucosal adjuvants. Our results and similar studies with enterotoxins that affect the paracellular barrier suggest that alteration of mucosal permeability may play an important role in the mechanisms of adjuvanticity.

Molecular Biology of the Clostridium difficile Toxins

Publisher Summary It causes a less severe, but more common, form of the disease termed antibiotic associated diarrhea (ADD). Clostridium difficile is now recognized as the primary cause of ADD in the United States. Toxins are the major virulence factors in C. difficile disease. Protection against toxins A and B are consistently found in fecal specimens from patients and experimental animals with the disease. Effective vaccination of experimental animals against the disease requires protection against both toxins. Most of the research on C. difficile disease has focused on purification and characterization of the molecular and biological properties of toxins A and B. Protein fractions attributed to purified toxin erroneously showed lower molecule weight proteins when analyzed by gel electrophoresis. Cloning, sequencing and expression of the toxin genes in Escherichia coli established that toxins A and B are the largest known bacterial toxins and are each composed of a single polypeptide. The toxins covalently modify low molecular weight guanine triphosphate (GTP)-binding proteins that regulate the actin microfilaments. A number of other clostridial enzymes modify the Rho family of proteins by adenosine diphosphate(ADP)-ribosylation.