Abstract:Objective To analyze the effect of smoking level on serum Th1/Th2/Th17 related cytokines in patients with community-acquired pneumonia.Method This retrospective study included 94 CAP patients (June 2022 to June 2024). Patients were categorized into infected smokers (stratified by smoking index: mild [< 400 pack-years], severe [≥ 400 pack-years] ) and non-smokers. Demographics, clinical parameters, and cytokine levels (IL-2, IL-4, IL-5, IL-17, IFN-γ, TNF-α) were compared.Result Infected smokers had higher lymphocyte counts, CRP, IL-4, IL-5, IL-17, but lower IL-2 than non-smokers (P < 0.05). Non-smokers showed higher IL-2, IL-4, IFN-γ, TNF-α than mild smokers, and lower IL-5 (P < 0.05). Severe smokers exhibited elevated IL-4, IL-5, TNF-α, IL-17 versus non-smokers (P < 0.05). IL-5 levels correlated with smoking index (P < 0.05).Conclusion Smoking suppresses Th1 and promotes Th2/Th17 responses in CAP, with cytokine dysregulation escalating with smoking intensity.