Obesity increases allergic airway inflammation that can be successfully treated by oral tolerance
Authors: Nora Geissler, Maria Orola, Masoumeh Alinaghi, Alexander Nardo, Thomas M. Stulnig, Joana Séneca, Anna Schmid, Elke Korb, Tatjana Svoboda, Erika Garner‐Spitzer, Michael Kundi, Monika Ehling‐Schulz, Irma Schabussova, Aleksandra Inic‐Kanada, Ursula Wiedermann
Journal: Allergy (2023)

The prevalence of obesity and allergy has increased in developed countries over the last decades,1, 2 leading to the hypothesis that these two noncommunicable diseases might be linked. It remains unclear whether obesity, characterized by chronic low-grade inflammation that affects host immunity, contributes to the exacerbation of respiratory allergies. Additionally, the efficacy of inducing mucosal tolerance as a prophylactic intervention against allergic airway disease in obese individuals is still a subject of inquiry. The impact of obesity on immune responses has been demonstrated in vaccinated individuals, revealing diminished vaccine efficacy and impaired duration of protection.3 Our current study investigates whether obesity could impact respiratory allergy development and the induction of mucosal allergen-specific tolerance. Male C57BL/6 mice fed with a high-fat diet (HFD) or standard chow diet (STD) for 9 weeks were immunized/sensitized and then challenged with ovalbumin (OVA) (Figure S1A). To induce allergen-specific tolerance, mice were orally treated with OVA before sensitization (Appendix S1). We detected significant differences in body weight between STD and HFD-fed mice, whereby HFD-fed mice had twice the body weight and significantly higher serum leptin levels than STD-fed mice at the time of sacrifice (Figure 1A,B). Fourier-transform infrared spectroscopy (FTIR) of the cecal content demonstrated distinct spectra between obese and lean mice (Figure 1C–F). These findings were confirmed by 16S rRNA gene sequencing, showing that gut microbial profiles of the cecal content significantly differed between obese and lean mice, consistent with other studies.4 Specifically, alpha (Figure 1G) and beta (Figure 1H) diversity results revealed that (i) the obese group exhibited significantly lower diversity levels than the lean group and (ii) microbial community structure was strongly affected by diet type (Figure 1I, S2, Table S1). Obesity exacerbates the allergic response in mice, with sensitization and challenge with OVA leading to significantly heightened manifestations compared to lean mice. This is evidenced by elevated levels of allergen-specific IgE in bronchoalveolar lavage (BAL) and serum (Figure 2A,B), as well as increased levels of IL-5 and IL-13 in the lungs (Figure 2C,D). Eosinophils, B cells, and T cells were upregulated in the lungs of allergic obese compared to allergic lean (Figure 2E,H,I), which explains the significantly higher OVA-specific IL-13 levels (Figure 2D) and exacerbated lung inflammation in the allergic obese group (Figure 2F,G). The rise in Tregs (Figure 2J) was also evident, and this increase could potentially be attributed to the overall expansion of T cells in allergic obese animals. Interestingly, obesity did not influence the capacity to develop oral tolerance (OT), and tolerized obese mice exhibited a nonallergic phenotype similar to that observed in lean animals. Our results demonstrate an efficient downregulation of allergic parameters upon tolerization (Figure 2A–J; Allergy vs. OT groups), including IgE levels locally and systemically (Figure 2A,B), OVA-specific IL-5/IL-13 (Figure 2C,D), and decreased lung inflammation (Figure 2F,G). Although significant differences were observed in microbial compounds, microbial diversity, and community structure between obese and lean mice (Figure 1C–I), no additional changes were evident based on the treatment (Allergy, OT, PBS) approach (Figure 2K–M). We hypothesized that a pro-inflammatory state in the gut of obese mice influenced the microenvironment in the mucus layer around the pulmonary tissue affecting different immune cells, including macrophages. We observed a shift in distributions of activated M1 and M2 macrophages in obese PBS-treated control relative to its lean counterpart. Allergic obese showed a significant reduction of M1 compared to the obese PBS control. At the same time, oral tolerance led to an M1/M2 distribution similar to the PBS-treated control group, with significantly more M1 macrophages (Figure 2N–P). Higher allergen-specific IL-13 levels in the lung of the allergic obese shown in our study could be accountable for altered functions of macrophages in allergic obese, initiating macrophage polarization toward the M2 phenotype. In conclusion, we show that oral tolerance induction could efficiently attenuate the increased allergic response and Th2-mediated lung inflammation associated with respiratory allergy in obese mice. Our results align with studies suggesting that M1 macrophages could be helpful in allergic diseases5, 6 and indicate that oral tolerance in obese and lean may be differently regulated due to a low-grade Th1 inflammatory state associated with increased leptin levels in obese. Therefore, we suggest that mucosal allergen-specific immunomodulation in obese mice functions mechanistically on two levels: (i) by efficiently reducing OVA-specific IL-5/IL-13 in the lungs and IgE in BAL and sera, and (ii) by maintaining and expanding the M1 macrophages in the lungs and thus protecting against Th2-mediated allergic responses. This study was funded by The Austrian Science Fund (FWF), project DK W1248-B30; the Government of Lower Austria (Land Niederösterreich), Danube-Allergy Research Cluster (P17); and the PhD Program Molecular, Cellular and Clinical Allergology (MCCA). U.W., A.I.K., and I.S. conceived the study. A.I.K. and U.W. supervised the experiments. N.G., A.I.K., and U.W. designed the experiments and interpreted the data. N.G. performed the experiments. M.O., E.G.S., A.N., and T.S. helped to establish the obesity animal model. M.A., T.S., and M.E.S., analyzed FTIR results. J.S., performed and analyzed 16S sequencing results. M.O., E.K., and A.S. helped with in vivo experiments. M.K. did a statistical analysis. N.G., U.W., and A.I.K. wrote and reviewed the manuscript. All authors have read and agreed to the final version of the manuscript. We thank our colleagues for contributing to this study: Tamara Weinmayer, Magdalena Wysmołek, Daniela Kerekes, Melissa Haunstetter, Mirjana Drinic, and Maria Ebert for their help with animal experiments and valuable discussions, and Susanne Glöckl for caring for our animals. We thank Bozidar Jokanovic for assistance in graphical design. The authors declare no conflicts of interest. The data that support the findings of this study are available from the corresponding author upon reasonable request. Figure S1 Figure S2 Table S1 Appendix S1 Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.