CXCL8 and chronic obstructive pulmonary disease: Fig. 3 shows Haemophilus has high abundance levels corresponding to COPD severity. Haemophilus can directly induce inflammation by recruiting neutrophils and increasing mucus production. Elevated sputum CXCL8/IL-8 levels are associated with high COPD severity [54]. At the phyla level, studies have shown that the most predominant microbiome phyla in the healthy lung are Firmicutes, Proteobacteria, and Bacteroidetes, respectively [50,51]. By considering the phylogenetic tree (Fig. S2), we observed the same phyla in both the healthy group and the COPD group (Table 2 and Fig. 4(a and b and c)).