Abstract
Community-acquired pneumonia due to Streptococcus pneumoniae occurs commonly in alcohol use disorders (AUDs). Pneumonia in the AUD patient is associated with poorer outcomes, and specific therapies to mitigate disease severity in these patients do not exist. Numerous investigations have attributed increased severity of pneumonia in AUDs to aberrant function of the alveolar macrophage (AM), a lung immune cell critical in host defense initiation. No studies have examined the response of human AMs to S. pneumoniae in AUDs. We hypothesized that the inflammatory mediators released by AMs after S. pneumoniae stimulation would differ quantitatively in individuals with AUDs compared to non-AUD participants. We further postulated that AM inflammatory mediators would be diminished after exposure to the antioxidant, N-acetylcysteine (NAC). For comparison, responses of peripheral blood mononuclear cells (PBMCs) to pneumococcal protein were also examined. Otherwise healthy participants with AUDs and smoking-matched controls underwent bronchoalveolar lavage and peripheral blood sampling to obtain AMs and PBMCs, respectively. Freshly collected cells were cultured with increasing doses of heat-killed S. pneumoniae protein, with and without exposure to N-acetylcysteine. Cell culture supernatants were collected, and inflammatory mediators were measured, including interferon (IFN)-γ, interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α. IFN-γ and IL-6 were significantly higher in unstimulated AM cell culture supernatants from subjects with AUDs. After stimulation with pneumococcal protein, a dose-response and time-dependent increase in pro-inflammatory cytokine production by both AMs and PBMCs was also observed; differences were not observed between AUD and non-AUD subjects. Addition of NAC to pneumococcal-stimulated AMs and PBMCs was generally associated with diminished cytokine production, with the exception of IL-1β that was elevated in AM culture supernatants from subjects with AUDs. Our observations suggest that AUDs contribute to basal alterations in AM pro-inflammatory cytokine elaboration, but did not support consistent differences in pneumococcal-stimulated AM or PBMC inflammatory mediator secretion that were referable to AUDs.