Eosinophil reduction attenuates remodeling in Samp1 mice

Abstract

The senescence-accelerated (SAMP1) mouse strain develops spontaneous ileitis and recapitulates the pathology of human Crohn's disease. Further examination of ileal tissue from this strain reveals significant eosinophilic infiltration and remodeling. We hypothesize that eosinophilic infiltration contributes to intestinal tissue remodeling. The aim of this study was to characterize the impact of α-CCR3 and α-IL-5 antibody treatment on eosinophilic infiltration and tissue remodeling in the SAMP1 model of Crohn's-like ileitis. Eosinophil inhibition studies were performed with single or combined α-CCR3 and/or α-IL-5 antibody injections during the chronic stage of disease, from 20 to 30 weeks, in SAMP1 mice. Flow cytometry for lamina propria leukocytes including eosinophils was performed. Histological features of ileitis in SAMP1 mice were assessed using H&E and Periodic Acid Schiff staining. Real Time PCR analysis was performed on ileal tissue for the TGF-β family, epithelial and mesenchymal markers of remodeling, collagen and extracellular matrix components, remodeling associated proteases, eotaxins, their receptors and mucin genes. All assessments were compared to age-matched control AKR mice. Blockade of lamina propria eosinophil infiltration was observed following 10-weeks of antibody infusion (α-CCR3 & α-IL-5; p<0.001) and resulted in attenuation of all indices of histological ileal inflammation (villus distortion, chronic and active inflammatory infiltrates) (α-IL-5; p<0.01, α-CCR3 & α-IL-5; p<0.01). Cellularity of both the spleen and reactive draining mesenteric lymph nodes were significantly reduced by combined antibody therapy (p= 0.03). Furthermore, flow cytometric analysis revealed a reduction in lamina propria central memory T-lymphocytes (CD4+ CD44high CD62-Lhigh). Reduction in tissue remodeling was also observed, as demonstrated by reduced muscle hypertrophy (α-CCR3; P<0.05, α-IL-5; p<0.01, α-CCR3 & α-IL-5; p<0.001) and reduced goblet cell hyperplasia (α-CCR3; P<0.01, α-IL-5; p<0.101, α-CCR3 & α-IL-5; p<0.001). The fibroblast chemo-attractant and eosinophil binding protein fibronectin, was the most increased gene during the progression of remodeling in these mice (20 fold; p<0.0001 at 20 weeks-of-age, 30 fold; p= 0.0007 at 40 weeks-of-age vs. age matched control AKR mice) and was significantly decreased following antibody treatment (α-CCR3; p<0.01). SAMP1 mice demonstrate Crohn's-like ileitis with histological and molecular features of eosinophilic infiltration and tissue remodeling. Antibodies against CCR3 and IL-5 are effective in reducing eosinophil infiltration, overall inflammation and tissue remodeling. We anticipate that this model will provide a valuable tool for further elucidating the eosinophil's role in the pathogenesis of inflammatory bowel diseases. This project was funded by a grant from NIH RO1DK62245&NIH R01DK080212-01A2.