IL-22 Is Deleterious along with IL-17 in Allergic Asthma but Is Not Detrimental in the Comorbidity Asthma and Acute Pneumonia

Abstract

There is evidence that IL-22 and IL-17 participate in the pathogenesis of allergic asthma. To investigate the role of IL-22, we used IL-22 deficient mice (IL-22 KO) sensitized and challenged with ovalbumin (OVA) and compared with wild type (WT) animals exposed to OVA. IL-22 KO animals exposed to OVA showed a decreased number and frequency of eosinophils, IL-5 and IL-13 in the airways, reduced mucus production and pulmonary inflammation. In addition, IL-22 KO animals exhibited a decreased percentage and number of lung CD11c⁺CD11b⁺ cells and increased apoptosis of eosinophils. Th17 cell transfer generated from IL-22 KO to animals previously sensitized and challenged with OVA caused a reduction in eosinophil frequency and number in the airways compared to animals transferred with Th17 cells generated from WT mice. Therefore, IL-22 is deleterious with concomitant secretion of IL-17. Our findings show a pro-inflammatory role for IL-22, confirmed in a model of allergen-free and allergen-specific immunotherapy. Moreover, during the comorbidity asthma and pneumonia that induces neutrophil inflammation, IL-22 was not detrimental. Our results show that targeting IL-22 would negatively affect the survival of eosinophils, reduce the expansion or migration of CD11c⁺CD11b⁺ cells, and negatively regulate allergic asthma.

Keywords: IL-17; IL-22; apoptosis; asthma; dendritic cell; eosinophil.

Figure 1

The allergic response is improved in the absence of IL-22. (A) WT and IL-22 KO mice were sensitized by administration of OVA (100 μg) and Aluminum Hydroxide (1.6 mg) by subcutaneous route (SC). On day 14, the animals received the second OVA sensitization (50 μg) via intraperitoneal route (IP). On day 21, the animals were challenged with OVA (100 μg) via the intranasal route (IN). (B) Total number of cells in BALF. (C,D) Differential and total count of BALF leukocytes. (E,F) Concentrations of IL-5 and IL-13 in the BALF supernatants. (G) Concentrations of anti-OVA IgE in the serum. The results are expressed as mean ± standard deviation of the individual values obtained for each experimental group. Results are representative of three independent experiments for BALF and cytokines and two independent experiments for antibodies. * p < 0.05; ** p < 0.01; *** p < 0.001; **** p < 0.0001. IP = intraperitoneal route, SC = Subcutaneous, IN = Intranasal.

Figure 2

Reduction in pulmonary inflammation and mucus production in the absence of IL-22. (A) Histopathological analysis of the lungs. Arrows show eosinophils. (B) Mucus production. Results are representative of three independent experiments. Top = magnification 200×; bottom = magnification 400×.

Figure 3

Th17 response is induced in allergic lung inflammation. (A,B) Concentrations of IL-22 and IL-17 in the BALF supernatants. (C–E) Concentrations of IL-1β, IL-23 and TGF-β in the BALF supernatants. (F,G) Frequency and representative analysis of CD4⁺IL-17⁺ cells, gated previously on CD4⁺ cells, in the lungs of mice exposed or not (PBS) to the allergen (OVA). Results were expressed as mean ± standard deviation of the individual values obtained for each experimental group. Results are representative of two independent experiments. * p < 0.05; ** p < 0.01; *** p < 0.001; **** p < 0.0001.

Figure 4

In the absence of IL-22, Th17 cells are protective in allergic asthma. (A) WT animals were sensitized and challenged, as previously described, and during the challenge, they received 4 × 10⁵ Th17 cells differentiated from naive CD4⁺CD62L⁺ cells from the spleen of WT or IL-22 KO animals. (B) Concentrations of IL-22 secreted by differentiated Th17 cells in vitro. (C,D) Representative flow cytometry analysis and frequency of differentiated Th17 cells in vitro. (E) Total number of cells in the BALF. (F,G) Frequency and total number of eosinophils in the BALF. Results are expressed as mean ± standard deviation of the individual values obtained for each experimental group. Results are representative of two independent experiments. * p < 0.05; ** p < 0.01; *** p < 0.001; **** p < 0.0001. IP = intraperitoneal route, SC = Subcutaneous, IN = Intranasal.

Figure 5

IL-22 modulates the frequency and number of dendritic cells, and eosinophil apoptosis in lungs of mice exposed to the allergen. WT and IL-22 KO mice were sensitized and challenged with OVA, as described in the legend of Figure 1A. (A) Representative flow cytometry analysis of CD11c⁺CD11b⁺CD103⁻ cells in the lungs. (B,C) Frequency and number of CD11c⁺CD11b⁺CD103⁻ cells in the lungs. (D) Representative flow cytometry analysis of MHC-II⁻Siglec-F⁺ cells and MHC-II⁻Siglec-F⁺AnnexinV⁺ cells. (E,F) Frequency and number of MHC-II⁻Siglec-F⁺ cells. (G,H) Frequency and number of MHC-II⁻Siglec-F⁺AnnexinV⁺ cells. The results are expressed as mean ± standard deviation of the individual values obtained for each experimental group. Results are representative of three independent experiments for DC and two independent experiments for eosinophil apoptosis. * p < 0.05; ** p < 0.01; *** p < 0.001; **** p < 0.0001.

Figure 6

Allergen-specific, allergen-free or simultaneous treatment reduces IL-22 production and dendritic cells in the lungs. (A) Mice were sensitized and challenged with OVA, followed by treatment with OVA by sublingual route, or CpG by subcutaneous route or with OVA and CpG simultaneously. Fifteen days after the end of immunotherapy, mice were challenged again with OVA, and evaluated 72 h post challenge. (B) Levels of IL-22 in the BALF. (C,D) Frequency and number of eosinophils in the BALF. (E,F) Frequency and number of CD11c⁺CD11b⁺ cells in the lungs of treated or non-treated animals. (G) Representative flow cytometry analysis of CD11c⁺CD11b⁺ cells in the lungs of treated or non-treated animals. The results are expressed as mean ± standard deviation of the individual values obtained for each experimental group. Results are representative of two independent experiments. The bars show the significant differences between groups ** p < 0.02; *** p < 0.01; **** p < 0.0001. IP = intraperitoneal route, SC = Subcutaneous, IN = Intranasal, SL = Sublingual.

Figure 7

IL-22 is not required for the exacerbation of neutrophilic inflammation in the comorbidity asthma and acute pneumonia. (A) WT and IL-22 KO animals were sensitized and challenged with OVA and infected or not with S. pneumoniae. (B,C) Differential and total count of leukocytes in the BALF. (D) Concentrations of CXCL-1 in the BALF supernatants. (E,F) Frequency of CD4⁺IL-17⁺ cells in the lungs. (G) Histopathological analysis of the lungs. Arrows and arrowheads show eosinophils and neutrophils, respectively. The results are expressed as mean ± standard deviation. Results are representative of three independent experiments. Top, magnification 200×; bottom, magnification 400×. The bars show the significant differences between groups * p < 0.05; ** p < 0.01; **** p < 0.0001.