Natural Pig Plasma Immunoglobulins Have Anti-Bacterial Effects: Potential for Use as Feed Supplement for Treatment of Intestinal Infections in Pigs

Hedegaard, Chris J.; Strube, Mikael L.; Hansen, Marie B.; Lindved, Bodil K.; Lihme, Allan; Boye, Mette; Heegaard, Peter M. H.

An indirect whole-cell ELISA was set up to assess the binding of ppIgG to relevant bacteria. We found that ppIgG bound to the bacterial surface of the three tested E. coli strains as well as S. diarizonae, however showed negligible binding to the fish pathogen Y. ruckeri (Fig 1B) . The avidity of ppIgG binding to E. coli ppIgG was tested by incubating an E. coli extract with ppIgG at 6 mg/ml and then subjecting it to increasing concentrations of urea for up to 30 minutes. Strong denaturing conditions (6 M urea, 30 minutes) significantly reduced the binding but never more than 35% (S1 Fig). Comparing the binding of IgG from either plasma or the purified IgG in the subsequent eluate to bacterial surface of E. coli revealed that the purification increased anti-E. coli titres with a factor 10 (S2 Fig). A competitive ELISA was used to evaluate the binding activity toward bacteria of the ppIgG as scored by its ability to out-compete a detection antibody having specificity for the bacterium in question, using ELISA plates coated with bacterial extract of either E. coli or S. diarizonae. Half-maximal inhibition was obtained with 2.4 mg/ml and 3.4 mg/ml of ppIgG on E. coli and S. diarizonae extracts, respectively (Fig 1C) . At least 1 mg/ml of ppIgG had to be applied in the competitive ELISA assay to obtain inhibition greater than 20%. Denaturation of ppIgG by heating to 70°C for 1 hour strongly decreased the binding (to 27% of the binding of native ppIgG; 5 mg/ml ppIgG on E. coli extract, Fig 1C) highlighting that the binding was dependent on the specific binding activity of ppIgG.