S. Deas1, J. Neilson1, K. Brawner1, C. Morrow2, C. Martin1 1University Of Alabama at Birmingham,Department Of Surgery,Birmingham, Alabama, USA 2University Of Alabama at Birmingham,Department Of Cell, Developmental, And Integrative Biology,Birmingham, Alabama, USA
Introduction: It is widely accepted that stress can negatively impact intestinal immune function. IgA is an established regulator of intestinal homeostasis and has been demonstrated to regulate bacterial translocation. The precise mechanism of how chronic psychological stress and bacterial dysrugulation affect the immune system and intestinal homeostasis is not known, but may be due to cortisol release by the hypothalamic-pituitary-adrenal (HPA) axis. We hypothesize that chronic stress and a state of dysbiosis impair intestinal immune function, perhaps mediated by dysregulation of the gut-brain immune axis.
Methods: 8-week-old C57BL/6 littermates were assigned to one of three experimental groups over a 7-day period. Group 1 was subjected to daily psychological stress via a well-established restraint model for one hour daily. Group 2 was given 1mg/mL vancomycin and 0.1mg/mL gentamicin in their drinking water to induce dysbiosis. Group 3 was subjected to both daily psychological stress and the antibiotic cocktail. The control group experienced no stress or antibiotic treatment. After the 7-day period, mesenteric lymph nodes (MLN) were harvested and cultured on Schaedler agar and incubated at 37°C for 3.5 days. Select bacterial colonies from our Group 3 MLNs were analyzed via 16S PCR for species identification. Enzyme-linked immunosorbent assay (ELISA) was utilized to measure fecal IgA and serum corticosterone levels.
Results: Microbial culture of MLN from the control group revealed minimal bacterial growth, with an average of 1.5 pinpoint colony forming units (CFUs) per plate. CFUs were difficult to quantify from other groups due to morphology. All experimental groups were characterized by irregular, raised, undulate growth. The 16S PCR analysis of isolates from Group 3 revealed that the predominant phylum involved in MLN translocation was Proteobacteria. Finally, the Group 2 had significantly less fecal IgA compared to the control group; P-value = 0.045*. The Group 3 had significantly less fecal IgA compared to Group 1; P-value = 0.0045# (Figure 1). There was no significant difference in serum corticosterone between the control and experimental groups.
Conclusion:
The combination of chronic stress and dysbiosis severely impairs the intestinal immune response, demonstrated by decreased fecal IgA. Serum corticosterone levels were not significantly different between control and experimental groups, suggesting that dysregulation of the HPA axis may not be the mechanism explaining the observed dampening of intestinal immunity. Bacterial translocation, as evidenced by MLN culture, indicates that this may be due to direct barrier dysfunction. Future experiments will seek to further elucidate this mechanism.
