Mast cells are required for experimental oral allergen–induced diarrhea (1)
Gastrointestinal allergic diseases are characterized by a wide array of manifestations, including elevated levels of IgE (total and antigen specific), eosinophilia, gastrointestinal dysfunction (e.g., vomiting and diarrhea), and/or systemic responses (e.g., hypotension and bronchospasm). Numerous mediators derived from these cells, including vasoactive amines (e.g., histamine and serotonin [5-hydroxytryptamine (5-HT)]), proteases (mucosal mast cell proteases-1–9 [MMCP-1–9]), leukotrienes, prostaglandins, platelet-activating factor (PAF), and a large array of cytokines, have been reported to be released during anaphylaxis.
Following this protocol, BALB/c mice developed diarrhea 15–45 minutes after the third OVA challenge. Although BALB/c mice started developing diarrhea acutely after the third intragastric challenge, C57Bl/6 mice were resistant to up to ten intragastric OVA challenges. Non Sensitized mice, who did not develop diarrhea, demonstrate that the observed diarrhea was not solely the result of an osmotic load in the gut, but rather an antigen-specific acute immunological response.
Hypothermia was significantly more severe in mice previously intragas- trically challenged with OVA compared with saline- challenged mice. Notably, lethal anaphylactic shock occurred only in mice that had previously developed gastrointestinal allergy. OVA-challenged mice had increased intestinal permeability to HRP. The antigen-induced increased permeability persisted at 48 hours.
IL-10 and IFN-γ mRNA were detected in all jejunum samples regardless of challenge number, in contrast to IL-4 and IL-13 mRNA, which were only detectable after two or three OVA challenges. Following allergen-induced diarrhea, plasma levels of total IgE were significantly higher in OVA-challenged mice compared with saline-challenged mice.
Comparison of allergen-challenged mice with saline-challenged mice revealed a decrease (less than 0.5-fold change over saline) in 53 genes and an increase (greater than twofold change over saline) in 530 genes. The two mast cell proteases classically associated with mucosal mast cells: MMCP-1 (40-fold increase) and MMCP-2 (17-fold increase). The increase in MMCP-1 transcript levels in the jejunum was substantiated by an impressive 5,000-fold increase in MMCP-1 plasma levels in OVA- challenged versus saline-challenged mice. The jejunum of OVA-challenged mice contained highly increased levels of mast cells compared with saline-challenged control mice.
Intestinal mast cells can be removed by treatment with an anti-c-kit Ab (ACK2). The efficiency of the treatment was validated by counting jejunum mast cell numbers and MMCP-1 plasma levels in mice treated with ACK2 or a control Ab (J1.2). Almost no MMCP- 1 was detected in plasma samples from ACK2-treated mice. Importantly, in the absence of mast cells, mice did not develop allergic diarrhea. Furthermore, intestinal permeability to HRP in the ACK2-treated mice was significantly decreased compared with J1.2-treated mice.
The treatment of an anti-FcγRII/RIII Ab (24G2) failed to block diarrhea occurrence in the present model, suggesting that diarrhea was not an FcγRIII-mediated process. Notably, when mice were pretreated with anti-IgE, the allergic diarrhea was markedly attenuated. After ten intragastric OVA chal- lenges, only 50% of FcεRI KO mice developed diarrhea, whereas all the control mice had diarrhea by the fifth challenge.
Notably, none of the tested drugs alone had any significant effect. A combination of all these drugs, or a combination of PAF and serotonin antagonists, however, significantly suppressed allergic diarrhea.
Degranulation of mucosal mast cells may only induce local mucosal and epithelial responses leading to diarrhea without provoking a massive release of histamine and serotonin in the bloodstreamDespite massive mucosal (but not connective tissue) mast cell degranulation, allergic diarrhea is not accompanied by anaphylactic shock (e.g., hypothermia or death).
Drugs that block 5-HT3 have also been reported to inhibit the net fluid secretion induced by cholera toxin and colonic transit in rats.