Objective To explore the relationship between airway mucosal immunological characteristics and bronchial mucus plug (BMP) in children with Mycoplasma pneumoniae pneumonia (MPP).

Methods A total of 120 children with MPP were selected as the study subjects and divided into BMP group (BMP was found during examination, n=45) and non-BMP group (no BMP was found during examination, n=75) according to the results of bronchoscopy. Enzyme-linked immunosorbent assay (ELISA) was used to detect the levels of cytokines interleukin (IL)-17A, IL-6, IL-8, IL-33, and C-X-C motif chemokine ligand 10 (CXCL10) in bronchoalveolar lavage fluid (BALF). Quantitative polymerase chain reaction (qPCR) was used to detect the expression of airway mucins (the relative mRNA expression levels of MUC5AC, MUC5B, MUC1, and MUC4). Navigation maps were drawn based on multi-slice spiral CT images, and bronchoscopy was performed on the children. The composition and α-diversity of the lower respiratory tract microbiota were analyzed by 16S rRNA gene sequencing. The hospitalization outcomes and pneumonia recurrence of the two groups of children were compared. Multivariate Logistic regression analysis was used to screen the influencing factors for the occurrence of BMP.

Results The levels of cytokines (IL-17A, IL-6, IL-8, IL-33, and CXCL10) in BALF were higher in the BMP group than those in the non-BMP group, and the differences were statistically significant (P < 0.05). The expression levels of MUC5AC mRNA and MUC5B mRNA were higher in the BMP group than those in the non-BMP group, and the differences were statistically significant (P < 0.05); there were no significant differences in the expression levels of MUC1 mRNA and MUC4 mRNA between the two groups (P>0.05). Compared with the non-BMP group, the features such as tree-in-bud sign, bronchial filling shadow, and plastic mucus plug were more significant in the BMP group during imaging and bronchoscopy, and the differences were statistically significant (P < 0.05). The microbial α-diversity in the BMP group was lower than that in the non-BMP group, and the relative abundances of Mycoplasma pneumoniae, Haemophilus influenzae, and Streptococcus pneumoniae were higher in the BMP group than those in the non-BMP group, with statistically significant differences (P < 0.05). The hospitalization duration of children in the BMP group was longer than that in the non-BMP group, the recovery rate of forced expiratory volume in one second at 90 days was lower than that in the non-BMP group, and the pneumonia recurrence rate and mechanical ventilation usage rate were higher than those in the non-BMP group, with statistically significant differences (P < 0.05). Multivariate Logistic regression analysis showed that tree-in-bud sign, high level of IL-17A, high expression of MUC5AC mRNA, and decreased α-diversity were effective predictive factors for the occurrence of BMP (P < 0.05).

Conclusion The IL-17A-driven inflammatory response, over-expression of goblet cell secretory mucin MUC5AC, and decreased α-diversity of the lower respiratory tract microbiota in the airways of children with MPP are all closely related to the occurrence of BMP.