TNF and metabolic disease: At this time, if pulmonary inflammation transmits systemic inflammatory signals through the gut–lung axis (such as TNF-α and IL-1β reaching the gut via blood circulation), the two sources of damage will produce a synergistic effect—both exacerbating the disruption of the intestinal barrier and amplifying the over-activation of gut immunity, thereby accelerating the imbalance of microbial structure and metabolic disorders.