Oral administration of bovine whey proteins to mice elicits opposing immunoregulatory responses and is adjuvant dependent

Abstract

SUMMARY Most studies investigating the induction of oral tolerance (OT) use purified proteins such as ovalbumin (OVA), bovine serum albumin (BSA) and beta-lactoglobulin (β-LG). Little information is available regarding the induction of OT to a protein mixture, e.g. cow's milk. In this study we compared the regulatory mechanisms induced after the oral administration of a whey protein concentrate (WP) derived from cow's milk following immunization with two different adjuvants, complete Freund's adjuvant (CFA) and alum. OVA was used as a control antigen. Animals were given a single feed of these proteins at an equivalent dose of 1 mg/g body weight before they were immunized seven days later with the antigen in Freund's adjuvant or alum. Delayed type hypersensitivity (DTH) responses were suppressed by both a feed of WP and OVA after immunization with CFA. However, only OVA feeding suppressed antigen specific IgG responses. In an attempt to investigate whether WP would tolerize the more susceptible IgE responses, alum immunization replaced CFA as the adjuvant used for systemic immunizations. WP, after a single feed, significantly primed for DTH and IgE responses indicating oral sensitization to WP. In contrast, OVA suppressed DTH, IgE and IgG responses. Antigen specific proliferation of mononuclear cells was suppressed in mice fed OVA, but primed in those fed with WP. In addition cells taken from sensitized mice fed WP up-regulated levels of specific interleukin (IL) -4, -10 and -12 in vitro whereas these cytokines were suppressed in cultures from tolerant WP fed mice. Global suppression was obtained in cultures from tolerant OVA fed mice. TGF-β was not detected in draining PLN cell cultures of either tolerant or sensitized mice. These data suggest that a whey protein mixture induces divergent responses following immunization with either CFA or alum despite being fed at an identical dose. We suggest that that the choice of the adjuvant may determine the immunoregulatory outcome and this is also reflected by the systemic cytokine profile.