Inflammation and mucus production are prevalent characteristics of chronic respiratory conditions, such as asthma and chronic chronic obstructive pulmonary disease (COPD). Biological co-factors, including bacteria, viruses, and fungi, may exacerbate these diseases by activating various pathways associated with airway diseases. An example is the fungus Pneumocystis, which is linked to severe COPD in human patients. Recent evidence has demonstrated that Pneumocystis significantly enhanced inflammation and mucus hypersecretion in a rat model of elastase-induced COPD. The present study specifically aims to investigate two additional aspects associated with the pathology induced by Pneumocystis infection: inflammation and collagen deposition around airways. To this end, the focus was to investigate the role of the IL-1β pro-inflammatory pathway during Pneumocystis infection in COPD rats. Several airway pathology-related features, such as inflammation, mucus hypersecretion, and fibrosis, were evaluated using histological and molecular techniques. COPD animals infected with Pneumocystis exhibited elevated inflammation levels, including a synergistic increase in IL-1β and Cox-2. Furthermore, protein levels of the IL-1β-dependent transcription factor cAMP response element-binding (CREB) showed a synergistic elevation of their phosphorylated version in the lungs of COPD animals infected with Pneumocystis, while mucus levels were notably higher in the airways of COPD-infected animals. Interestingly, a CREB responsive element (CRE) was identified in the Muc5b promoter. The presence of CREB in the Muc5b promoter was synergistically increased in COPD animals infected with Pneumocystis compared to other experimental groups. Finally, an increment of deposited collagen was identified surrounding the airways of COPD animals infected with Pneumocystis compared with the other experimental animal groups and correlated with the increase of Tgfβ1 mRNA levels. These findings emphasize the role of Pneumocystis as a potential biological co-factor in chronic respiratory diseases like COPD or asthma, warranting new perspectives in the treatment of chronic respiratory diseases.

Chronic Obstructive Pulmonary Disease (COPD) is characterized by persistent inflammation and structural alterations in the lung triggered mainly by oxidative stress. Colonization by the opportunistic fungus Pneumocystis has been associated with worse clinical outcomes in COPD, yet its role in airway remodeling remains unclear. To this end, an elastase-induced COPD model was established, followed by colonization with Pneumocystis. Lung tissue was analyzed histologically and molecularly to assess epithelial thickness, alveolar morphometric parameters (mean linear intercept [MLI], D₀, D₁, D₂), inflammation, collagen deposition, and the expression of remodeling and oxidative stress markers. Emphysematous damage parameters MLI, D₀, D₁, and D₂ were markedly elevated in co-exposed animals, indicating enhanced alveolar enlargement. Animals with COPD and Pneumocystis colonization showed a significant increase in airway inflammation compared with control, COPD, and Pneumocystis groups. Airway epithelial thickness, mucus metaplasia, and collagen deposition exhibited a summative increase in the COPD/Pneumocystis group. Redox-responsive markers, such as superoxide dismutase (SOD) and catalase, were upregulated. Moreover, protein and mRNA levels of nuclear factor erythroid 2–related factor 2 (Nrf2) and its downstream gene heme oxygenase-1 (Hmox1) were significantly increased, with the strongest activation observed in co-exposed animals. Integrative correlation analysis showed that Pneumocystis burden positively correlated with lung damage, inflammation, and epithelial remodeling. These structural alterations were accompanied by coordinated activation of the antioxidant pathway Nrf2. Taken together, Pneumocystis colonization is associated with enhanced pulmonary remodeling and modulation of antioxidant signaling in experimental COPD, promoting structural and molecular changes that may contribute to disease progression. These findings suggest that Pneumocystis acts as an amplifying factor in COPD-associated lung damage.