Cigarette smoke induces apoptosis in the follicle-associated epithelium of murine Peyer's patches

Background: Recently, cigarette smoking has been associated with the development of several auto-immune diseases, including rheumatoid arthritis and inflammatory bowel disease (IBD). The cellular and molecular mechanisms through which cigarette smoking predisposes to IBD are unknown. Cigarette smoke-induced apoptosis is described in several in vivo and in vitro experiments, and might play a role in the pathogenesis of several smoke-associated diseases. The aim of this study was to quantify apoptosis in normal murine Follicle-Associated Epithelium (FAE) and compare this to apoptosis in FAE of smoking mice. Methods: 8 C57BL/6 male mice were exposed to cigarette smoke for 24 weeks (chronic exposure); a control group of 8 mice was exposed to air during the same period. After 24 weeks the mice were sacrificed and Peyer’s patches of each mouse were dissected for histology. Immunohistochemistry for caspase-3 was performed on paraffin-embedded tissue sections of 11 Peyer’s patches of smoking animals and 11 Peyer’s patches of controls. To compare apoptotic activities between smokers and controls, the apoptotic index (percentage of apoptotic cells per 100 cells) in the FAE was calculated. An unpaired student T-test was applied. Results: A statistically significant increase in apoptosis of FAE cells was observed in smoking mice compared to air-exposed mice (P=0.002). In the FAE of smoking animals, the mean apoptotic index was 1.82 with a range of 1.11 to 3.00, whereas the mean apoptotic index in non-smoking animals was 0.92 (range 0.24 -2.06). Most apoptotic cells in both groups were seen at the apex of the FAE. Conclusion: We quantified rates of apoptosis in the FAE of murine Peyer’s patches. Furthermore we compared apoptosis in the FAE of smoking mice versus non-smoking siblings and observed an increased apoptotic index in the FAE of smoking animals. Our results demonstrate that cigarette smoke induces a significant increase of apoptosis in the FAE of murine Peyer’s patches and may point to a role for smoking in the pathogenesis of intestinal inflammation. Further investigation needs to clarify whether this increase in apoptosis influences normal function of the FAE