Polymeric IgA is superior to monomeric IgA and IgG carrying the same variable domain in preventing Clostridium difficile toxin A damaging of T84 monolayers

The two exotoxins A and B produced by Clostridium difficile are responsible for antibiotic-associated enterocolitis in human and animals. When added apically to human colonic carcinoma derived T84 cell monolayers, toxin A, but not toxin B, abolished the transepithelial electrical resistance and altered the morphological integrity. Apical addition of suboptimal concentration of toxin A made the cell monolayer sensitive to toxin B, Both toxins induced drastic and rapid epithelial alterations when applied basolaterally with a complete disorganization of tight junctions and vacuolization of the cells, Toxin A-specific IgG2a from hybridoma PCG-4 added apically with toxin A alone or in combination with toxin B abolished the toxin-induced epithelial alterations for up to 8 h, The Ab neutralized basolateral toxin A for 4 h, but not the mixture of the two toxins, Using an identical Ab:Ag ratio, we found that recombinant polymeric IgA (IgA(d/p)) with the same Fv fragments extended protection against toxin A for at least 24 h in both compartments. In contrast, the recombinant monomeric IgA counterpart behaved as the PCG-4 IgG2a Ab, The direct comparison between different Ig isotype and molecular forms, but of unique specificity, demonstrates that IgA(d/p) Ab is more efficient in neutralizing toxin A than monomeric IgG and IgA, We conclude that immune protection against C, difficile toxins requires toxin A-specific secretory Abs in the intestinal lumen and IgA(d/p) specific for both toxins in the lamina propria.