Commonly Used Drugs Impair Oral Tolerance in Mice

Effective induction of oral anaphylaxis to ovalbumin in mice sensitized by feeding of the antigen with aid of oil emulsion and salicylate

It is important to evaluate the ability of novel proteins in food crops and products to elicit potentially harmful immunologic responses, including allergic hypersensitivity. We developed a novel mouse model of food allergy involving an oral challenge of a protein antigen after feeding of the antigen in combination with modulating factors often ingested in daily life, namely, dietary oil emulsion and salicylate. In the model, BALB/c mice were sensitized orally for three weeks with ovalbumin (OVA) in linoleic acid/lecithin emulsion, followed immediately by intraperitoneal injection of sodium salicylate. At the end of the sensitization, the incidence of mice positive for serum OVA-specific IgG1 but not IgE had significantly increased in the combined-sensitization group. After the 3-week sensitization, a single or double oral challenge with OVA effectively and significantly caused severe anaphylaxis, as compared with the groups sensitized with OVA in the emulsion or the vehicle alone. Moderate increase of plasma histamine and intestinal abnormality in histology was found only in the combined-sensitization group. Anaphylaxis symptoms in the sensitized mice were induced more by oral challenge than by intravenous challenge, suggesting a critical role for the mucosal system. This is the first model for successful induction of oral anaphylaxis in mice sensitized by feeding of food protein without adjuvant. It will be useful to elucidate the mechanism of food allergy and to detect modulating factors of oral allergy at sensitization using this model, which simulates real life conditions.

Erythromycin treatment hinders the induction of oral tolerance to fed ovalbumin

The mucosal immune system is constantly exposed to antigen, whether it be food antigen, commensal bacteria, or harmful antigen. It is essential that the mucosal immune system can distinguish between harmful and non-harmful antigens, and initiate an active immune response to clear the harmful antigens, while initiating a suppressive immune response (tolerance) to non-harmful antigens. Oral tolerance is an immunologic hyporesponsiveness to an orally administered antigen and is important in preventing unnecessary gastrointestinal tract inflammation, which can result in a number of autoimmune and hypersensitivity diseases. Probiotics (beneficial intestinal bacteria), T regulatory cells, and dendritic cells (DCs) are all essential for generating tolerance. Antibiotics are commonly prescribed to fight infections and often necessary for maintaining health, but they can disrupt the normal intestinal probiotic populations. There is increasing epidemiologic evidence that suggests that antibiotic usage correlates with the development of atopic or irritable bowel disorders, which often result due to a breakdown in immune tolerance. This study investigated the effect of the antibiotic erythromycin on oral tolerance induction to ovalbumin. The results demonstrated that antibiotic treatment prior to exposure to fed antigen prevents tolerance to that antigen, which may be associated with a reduction in intestinal Lactobacillus populations. Furthermore, antibiotic treatment resulted in a significant decrease in the tolerogenic CD11c⁺/CD11b⁺/CD8α^- mesenteric lymph node DCs independent of tolerizing treatment. These results provide evidence that antibiotic treatment, potentially through its effects on tolerogenic DCs and intestinal microflora, may contribute to autoimmune and atopic disorders via a breakdown in tolerance and support prior epidemiologic studies correlating increased antibiotic usage with the development of these disorders.

Mucosal Tolerance to KLH Reduces BSA-Induced Arthritis in Rats—An Indication of Bystander Suppression

Mucosal tolerance has been shown to reduce disease severity in animal models mimicking human autoimmune diseases. The objective of this study was to examine whether mucosal tolerance against keyhole limpet haemocyanin (KLH) could be used to reduce bovine serum albumin (BSA)-induced arthritis in rats and whether anti-inflammatory drugs or passive cigarette smoke affected tolerance induction. Arthritis was induced by immunizing rats with BSA and then injecting BSA into one knee and saline into the other knee for comparison. Prior to BSA immunization, the rats were treated intranasally with KLH or saline and KLH then injected in the knee joints at the time of BSA injection, or the rats were treated with or without anti-inflammatory drugs or subjected to cigarette smoke prior to and during intranasal treatment with BSA. The rats that received intranasal treatment with KLH had a significantly less inflammation in their left knee joint compared to rats that received intranasal saline treatment. Beclamethasone increased the tolerance effect of BSA, whereas passive cigarette smoke abrogated the mucosal tolerance. This data suggests that bystander suppression can be used to treat arthritis and other autoimmune diseases, even when the autoantigen is not known.

Antibiotic administration early in life impairs specific humoral responses to an oral antigen and increases intestinal mast cell numbers and mediator concentrations

In this study, we assessed the effect of administering the antibiotic amoxicillin to rat pups on the immune response to orally fed ovalbumin (OVA). We first established that amoxicillin administration durably altered the gut microbiota of these animals. In parallel, we observed that the induction of the specific humoral response to ovalbumin was impaired when it occurred during antibiotic administration to the rat pups. We also examined the consequences of those observations on further allergic reactions. Amoxicillin administration had no significant impact on subsequent sensitization to OVA, as nonexacerbated systemic allergic responses were induced in antibiotic-treated animals. However, increased rat mast cell protease II levels and higher mast cell numbers were detected in their small intestines, independently of the antigen administration. Globally, our data suggest that antibiotic administration early in life negatively affects the specific immune response to a luminal antigen when it is first introduced during antibiotic administration. The increased mast cell numbers and mediator concentrations in the intestinal mucosae of the antibiotic-treated animals may testify to the early stages of an altered immune system homeostasis.