There are 8 clusters: the pink cluster (inflammation, cancer, myocardial infarct, etc.), purple cluster (IL-18, IL-1β, rheumatoid arthrit, etc.), orange cluster (airway inflammation, TNF-α, allergy, etc.), blank cluster (IL-13, pathogenesis, epithelial cells, etc.), blue cluster (COPD, severe asthma, rhinovirus, etc.), green cluster (biomarker, IGE, dendritic cells, etc.), yellow cluster (eosinophilia, IL-37, alarmin, etc.), and red cluster (prognosis, IL-25, basophil, etc.).These indicate that keywords in the same cluster are more important research hotspots during the same period. Here, TNF is linked to chronic obstructive pulmonary disease.