Helper T-cell type 17 cytokines and immunity in the lung

Peripheral immunological characteristics of spontaneous pneumothorax: a Mendelian randomization study

Background

Spontaneous pneumothorax (SP) is a common pleural disease in adolescents and adults. However, the role of immunological characteristics in the pathogenesis of SP remains unclear. This study aims to clarify the causal associations between circulating immune cells, lymphocyte subgroups, and SP susceptibility.

Methods

Employing Mendelian randomization (MR), the causal association between circulating immune blood cells and lymphocyte subgroups on SP susceptibility have been assessed. Reverse MR analysis was used to further explore the causal relationship. The MR analysis ensured the reliability of the study results through the deletion of confounding single nucleotide polymorphisms (SNPs), heterogeneity testing, sensitivity analysis.

Results

Seven immune cells and SP risk under stringent and lenient threshold conditions were identified. Eosinophils absolute count (AC) [odds ratio (OR) =1.0014, 95% confidence interval (CI): 1.0001-1.0014, P=0.02], memory B cell %B cell ratio (OR =1.008, 95% CI: 1.0002-1.0015, P=0.01), CD4+ T cell AC (OR =1.0014, 95% CI: 1.0003-1.0025, P=0.009), effector memory CD4+ T cell %T cell ratio (OR =1.0028, 95% CI: 1.0010-1.0046, P=0.003), and HLA-DR+CD8+ T cell %T cell ratio (OR =1.0019, 95% CI: 1.0004-1.0035, P=0.01) were identified as risk factors for increased susceptibility to SP. Conversely, CD8dim T cell AC (OR =0.9983, 95% CI: 0.9967-0.9999, P=0.03) and CD8dim natural killer T (NKT) %T cell ratio (OR =0.9982, 95% CI: 0.9965-0.9999, P=0.04) exhibited protective effects on SP. In natural killer (NK) cell subgroups and reverse MR analysis, no significance was found.

Conclusions

This study establishes a close causal relationship between immune cells and SP through genetic methods, providing a new perspective for understanding the pathophysiological mechanisms of SP.

Pulmonary Interleukin-17-Positive Lymphocytes Increase during Pneumocystis murina Infection but Are Not Required for Clearance of Pneumocystis

Pneumocystis remains an important pathogen of immunosuppressed patients, causing a potentially life-threatening pneumonia. Despite its medical importance, the immune responses required to control infection, including the role of interleukin-17 (IL-17), which is important in controlling other fungal infections, have not been clearly defined. Using flow cytometry and intracellular cytokine staining after stimulation with phorbol myristate acetate and ionomycin, we examined gamma interferon (IFN-γ), IL-4, IL-5, and IL-17 production by lung lymphocytes in immunocompetent C57BL/6 mice over time following infection with Pneumocystismurina We also examined the clearance of Pneumocystis infection in IL-17A-deficient mice. The production of both IFN-γ and IL-17 by pulmonary lymphocytes increased during infection, with maximum production at approximately days 35 to 40, coinciding with peak Pneumocystis levels in the lungs, while minimal changes were seen in IL-4- and IL-5-positive cells. The proportion of cells producing IFN-γ was consistently higher than for cells producing IL-17, with peak levels of ∼25 to 30% of CD3+ T cells for the former compared to ∼15% for the latter. Both CD4+ T cells and γδ T cells produced IL-17. Administration of anti-IFN-γ antibody led to a decrease in IFN-γ-positive cells, and an increase in IL-5-positive cells, but did not impact clearance of Pneumocystis infection. Despite the increases in IL-17 production during infection, IL-17A-deficient mice cleared Pneumocystis infection with kinetics similar to C57BL/6 mice. Thus, while IL-17 production in the lungs is increased during Pneumocystis infection in immunocompetent mice, IL-17A is not required for control of Pneumocystis infection.

IL-17A impairs host tolerance during airway chronic infection by Pseudomonas aeruginosa

Resistance and tolerance mechanisms participate to the interplay between host and pathogens. IL-17-mediated response has been shown to be crucial for host resistance to respiratory infections, whereas its role in host tolerance during chronic airway colonization is still unclear. Here, we investigated whether IL-17-mediated response modulates mechanisms of host tolerance during airways chronic infection by P. aeruginosa. First, we found that IL-17A levels were sustained in mice at both early and advanced stages of P. aeruginosa chronic infection and confirmed these observations in human respiratory samples from cystic fibrosis patients infected by P. aeruginosa. Using IL-17a^−/− or IL-17ra^−/− mice, we found that the deficiency of IL-17A/IL-17RA axis was associated with: i) increased incidence of chronic infection and bacterial burden, indicating its role in the host resistance to P. aeruginosa; ii) reduced cytokine levels (KC), tissue innate immune cells and markers of tissue damage (pro-MMP-9, elastin degradation, TGF-β₁), proving alteration of host tolerance. Blockade of IL-17A activity by a monoclonal antibody, started when chronic infection is established, did not alter host resistance but increased tolerance. In conclusion, this study identifies IL-17-mediated response as a negative regulator of host tolerance during P. aeruginosa chronic airway infection.