Reduction in virus-neutralizing activity of a bovine colostrum immunoglobulin concentrate by gastric acid and digestive enzymes.

Bovine milk immunoglobulin concentrates have been proposed for inducing passive immunity against various enteric pathogens. In vitro digestion studies were conducted to evaluate the effect of gastrointestinal secretions on the virus-neutralizing activity of a concentrate prepared from the colostrum of cows that were immunized with rotavirus. The proteolytic activity of human gastric and duodenal fluid specimens was used to design a two-stage in vitro digestion model with commercial enzymes for estimating the individual impact of pepsin, gastric acid, and select pancreatic enzymes on antirotavirus activity in bovine milk immunoglobulin concentrates. The rotavirus-neutralizing titer of concentrate was decreased by incubation with pepsin at pH 2, a pool of pancreatic enzymes at pH 7.5, or sequential digestion with pepsin (pH 2) and pancreatic enzymes (from initial titer of 55,210 to 2,030, 19,500, and 320, respectively). Reduction in rotavirus-neutralizing titer after gastric-phase digestion was primarily due to acidic conditions and not to proteolytic cleavage by pepsin. Although both trypsin and carboxypeptidase caused significant proteolysis of concentrate during duodenal-phase digestion, only trypsin caused a significant reduction in rotavirus-neutralizing titer. The extent of digestion was the same for concentrate suspended in water or skim milk. The results demonstrate that the biological activity of bovine milk antibodies is reduced by exposure to acid and trypsin in vitro and suggest that neutralization of both gastric acid and pancreatic trypsin may enhance the effectiveness and economic feasibility of passive oral immunoprophylaxis with bovine milk immunoglobulins.