THE FOOTPRINT OF HYPERCAPNIA ON INFLAMMATORY PATHWAYS DURING BACTERIAL INFECTION

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Pneumonia frequently occurs under hypercapnic conditions. Previous studies in hypercapnic models have reported that elevated CO 2 levels inhibit the NF-κB pathway, resulting in reduced inflammation. Notably, our prior work demonstrated that hypercapnia combined with bacterial infection increased IL-1β secretion. To study how hypercapnia affects the expression of key inflammation-related genes in in vitro models of macrophages (THP-1) and co-cultures with alveolar epithelium (HPAEpiC) following infection with Pseudomonas aeruginosa (PA) or Streptococcus pneumoniae (SP). Macrophage-like THP-1 cell monocultures and co-cultures of HPAEpiC and THP-1 cells were infected with PA or SPNE for 1 h and maintained for 24 h under normocapnia, hypercapnia, or reverted hypercapnia. Expression of inflammatory markers was analysed by RT-qPCR. Hypercapnia enhanced IL-1β expression in infected cultures, with NLRP3 upregulated in PA infection. IRAK1 expression was inhibited under hypercapnia, particularly in co-cultures. RIPK1 was stable in monocultures but increased in co-cultures under hypercapnia. Reversion to normocapnia restored inflammatory levels in monocultures but only partially in co-cultures. Hypercapnia amplifies pro-inflammatory responses to bacterial infection, partly through alternative pathways beyond canonical NF-κB signalling. In co-culture, these effects are further modulated by interactions with alveolar epithelial cells.

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