Immunisation of mares with binding domains of toxins A and B of Clostridium difficile elicits serum and colostral antibodies that block toxin binding.

This research studied whether immunising pregnant horses with parts of two toxins produced by Clostridium difficile (C. difficile) bacteria can generate antibodies that neutralise these toxins. The research indicates this approach may provide a way to thwart infections in young foals, supporting the idea of developing a vaccine to protect them.

Objective and Method

• The study’s main aim was to see if antibodies created in pregnant mares against the binding regions of two toxins (TcdA and B), produced by C. difficile, could neutralise these toxins.
• The researchers isolated sequences (or binding domains) encoding for these toxins through a technique called PCR (polymerase chain reaction) from a C. difficile strain isolated from a foal.
• They then transferred these sequences into a different bacterial type, giving us the proteins associated with toxins A and B.
• Thirteen pregnant mares were given two doses of these proteins, mixed with a substance known as Quil A, to induce their immune systems to produce antibodies against the two toxins.
• The level of these antibodies in blood and colostrum (initial breast milk) were then measured through a test known as ELISA, and their ability to block the toxins’ impact on horse endothelial cells (cells lining the inside of blood vessels) was assessed.

Results

• All pregnant mares produced strong antibody responses to the binding domains of each toxin.
• The researchers also found a high level of toxin-specific antibodies in colostrum, and in most foals’ blood samples taken two days after they suckled this colostrum.
• When the researchers mixed diluted blood and colostrum with either one of toxins and added to endothelial cells, cells remained healthy.
• In contrast, similar concentrations of toxins, either alone or mixed with blood or colostrum from non-immunised mares or foals led to damage in cells ranging from complete breakdown to some degree of change in cell shape.

Conclusions

• The study concludes that immunising pregnant mares with parts of toxins A and B from C. difficile leads to the production of specific antibodies in blood and colostrum that blocked the harmful impacts of these toxins.
• Based on these results, the researchers suggested that it could be feasible to create a vaccine to protect young foals against enterocolitis caused by C. difficile, by immunising the mares before giving birth.