Influence of Gastrointestinal Food Allergy On Colonic Immune Activation and Barrier Integrity in the Irritable Bowel Syndrome

Nematode infection results in a polarized Th2 cytokine response and development of alternatively activated macrophages (AAMΦ).IL-13 upregulation of 5-HT2A and PAR-2 is essential for infection-induced changes in smooth muscle hypercontractile response to 5-HT and the PAR-2 agonist, SLIGRL, respectively. Little is known, however, about the interaction between macrophages and these mediators.Aim:To determine the interaction between IL-13 and 5HT or SLIGRL on macrophage development.Methods: Macrophages were collected from uninfected C57BL/6 mice (naive) by peritoneal lavage 4 days after intraperitoneal injections of thioglycate. Macrophages were plated and exposed to vehicle, PAR-2 agonist, SLIGRL(200μM), or 5-HT(50μM)in the presence or absence of IL-13(10ng/ml)for 24 hours. Macrophages were harvested and real-time PCR was used to measure mRNA expression of specific markers. To determine the persistence of these effects we studied macrophages harvested from mice 20 weeks post H. polygyrus(Hp)infection (primed).Results:In naive macrophages, IL-13 upregulated expression of the AAMΦ marker, arginase-1 (1.0±0.1 vs 4.6±1.3 fold). Exposure of naive macrophages to SLIGRL (1.4±0.9 fold) or 5-HT (0.5±0.01) alone did not affect expression of arginase-1; however, SLIGRL markedly potentiated the effects of IL-13 on arginase-1 (4.6±1.3 vs 23.8±0.9). In macrophages harvested from previously Hp infected mice (primed), expression of AAMΦmakers was not different from control. Exposure to SLIGRL or 5-HT alone significantly upregulated by arginase1 and CD206 (table). The effect of SLIGRL was associated with increased expression of PAR-2 (1±0.9 vs 4.9±1.7 fold) as well as IL-4Rα (1±0.1 vs 2.3±0.5 fold) and IL-13Rα1 (1±0.2 vs 3.1±0.3), the receptor components for the type-2 IL-4 receptor that binds IL-13.Conclusions:During infection, exposure to PAR-2 agonists promotes the development of AAMΦ critical for the infection induced changes in smooth muscle contractility. Long lasting effects of infection include the ability of PAR-2 agonists or 5-HT to induce the AAMΦ phenotype by increasing the sensitivity of macrophages to IL-13. This may be important in the development of a Th2 memory response and the persistent effects of infection on gut function.