Peptic fragments of bovine serum albumin bind antigen-specific T suppressor cells from orally tolerized mice

Acid suppression therapy and allergic reactions

The development of pharmaceutical agents such as sucralfate, histamine 2 (H2) receptor blockers and proton pump inhibitors (PPIs) reducing gastric acidity has been a mile stone for treatment of dyspeptic disorders. However, due to current prescription habits resulting in overuse of these potent drugs as well as over-the-counter (OTC) availability associated with self-medication, substantial health concern is related to the mechanisms of drug action as well as known side effects influencing gastrointestinal physiology. More than a decade ago the first study appeared reporting an association between anti-ulcer drug intake and food allergy development. Ever since this first report several experimental as well as human studies verified this correlation, demonstrating that acid suppressive drugs not only influence the sensitization capacity of orally ingested proteins, but also represent a risk factor for food allergy patients. Additionally, gastric acid suppression was reported to increase the risk for development of drug hypersensitivity reactions. These consequences of anti-ulcer drug intake might on the one hand be associated with direct influence of these drugs on immune responses. On the other hand reduction of gastric acidity leads to impaired gastrointestinal protein degradation. Nevertheless, also disruption of the gastrointestinal barrier function, changes in microbiome or lack of tolerogenic peptic digests might contribute to the connection between anti-ulcer drug intake and allergic reaction. Therefore, these drugs should only be prescribed based on a precise gastroenterological diagnosis taking into consideration allergological mechanisms to ensure patients' safety.

Induction of systemic immunologic hyporesponsiveness to ovalbumin in neonatal rats by the enteric administration of peptic fragments of ovalbumin

The orogastric administration of protein antigens can induce specific systemic immunologic hyporesponsiveness to the antigens. Some evidence has suggested that fragmention of the antigens by proteolytic enzymes in the gastrointestinal tract is a necessary step in this phenomenon. We administered either ovalbumin (OVA) or fragments OVA, produced by digestion with pepsin, into the stomach or jejunum of suckling rats and measured the serum IgG antibody response to a subsequent intraperitoneal challenge with OVA. Whereas OVA administered by gastric gavage caused virtually a complete unresponsiveness to the OVA challenge, administration into the jejunum had no significant effect. Administration of peptic fragments of OVA (about 8000 Da) into either the jejunum or stomach caused systemic unresponsiveness in 62% and 67% of animals, respectively (p < .05 vs buffer-fed controls). Smaller fragments of OVA (< 2000 Da) given into the stomach or jejunum had no effect on systemic IgG responses, nor did administration of the 8000 Da fragments intraperitoneally. We conclude the 1) systemic immunologic tolerance to OVA can be induced by enteric administration of critical-size fragments of OVA, and 2) encounter of the OVA fragments, like intact OVA, via the gut yields a distinctly different response from that which follows parenteral administration.

Aberrant tolerance induction with cationic antigens

We studied the induction of tolerance in female C57B1/6 mice by oral and intravenous (i.v.) administration of protein antigens before immunization. Native proteins [chicken egg albumin (OVA), bovine serum albumin (BSA)] and their cationic derivatives [amidated (a)OVA, aBSA, methylated (m)BSA] were compared in their capacity to suppress cell-mediated immunity (CMI), as measured by a delayed type hypersensitivity test (DTH). Oral feeding of 0.5 mg negative proteins gave a clear suppression. By contrast, cationic derivatives (50 micrograms to 50 mg) did not suppress CMI. Data from cross-experiments, where aOVA was fed in OVA-immune mice, showed no suppression at all. When OVA was fed in aOVA-immune mice, only a partial suppression was achieved. The potency to induce tolerance differed also when the antigens were administered i.v.: 25 micrograms OVA was sufficient to induce a clear suppression, whereas a much higher amount of aOVA (500 micrograms) caused marginal suppression in OVA- and aOVA-immune mice, respectively. Nevertheless, when concentrations of aOVA up to 2.5 mg were tested in a chronic model of arthritis, a significant suppression was achieved. The differences in inducing a CMI suppression may have implications for the feasibility of immunointervention. Successful modulation of human arthritis may be highly dependent on the nature of the antigen involved.

The role of digestive enzymes in orally induced immune tolerance

The influence of digestive enzymes on the tolerogenic properties of an orally administered protein antigen, Bovine Serum Albumin (BSA), in the mouse has been investigated. A non-immunogenic peptic digest of BSA was found to be immunosuppressive when administered orally or directly injected into the mouse ileum. In contrast, untreated BSA was tolerogenic when administered orally but immunogenic following ileal administration. As determined by precipitin analysis of the proteins recovered from mouse feces, orally administered BSA was thoroughly degraded by the digestive system while the degradation in the ileum was quite limited. We conclude that to acquire tolerogenic properties, an orally administered protein must be first degraded by the proteolytic enzymes of the gastrointestinal digestive system.

Immunologic outcome of enteric administration of ovalbumin to neonatal rats is anatomic-site specific

An important immunologic response to the oral ingestion of a protein antigen is systemic tolerance to subsequent parenteral encounter with the same antigen. In the newborn intestine, ileal epithelial cells nonspecifically take up macromolecules and degrade them in lysosomal enzyme-containing vacuoles. We speculated that processing of protein antigens by the ileal cells helps mediate systemic immunologic tolerance to the antigens. Therefore, we developed a neonatal rat model in which ovalbumin (OVA) was administered either by gastric gavage or by infusion into surgically constructed loops of jejunum or ileum. We also administered OVA to other groups of animals by injection into the intact jejunum or ileum. Two and 4 weeks later, animals were challenged with OVA measured. Whereas animals that received OVA by gastric gavage were made tolerant to the protein (produced no detectable serum IgG anti-OVA antibodies after parenteral challenge), the animals given OVA into the jejunum or ileum did not show tolerance; indeed, some of those given OVA into the ileum were immunized by the enteric exposure. From these data we postulate that the development of systemic immunologic tolerance to a protein antigen in the newborn requires "upstream" processing of the antigen by gastric or pancreatic secretions and that exposure of the distal intestine to intact protein antigens can result in systemic sensitization to the antigens. The latter response might be causally linked to food allergies or autoimmune diseases.