Although there has been no direct evidence suggesting the relationship between H. pylori and NTIS to date, a study investigating the link between NTIS and chronic obstructive pulmonary disease (COPD) found that tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) were significantly higher in NTIS patients (29). Here, TNF is linked to chronic obstructive pulmonary disease.