Abstract:

Objective To investigate the characteristics of T-cell subset changes in children with refractory Mycoplasma pneumoniae pneumonia（RMPP） after bronchoscopy and their relationship with disease outcomes. Methods A total of 126 children with RMPP in Hefei Second People's Hospital from July 2021 to April 2023 were enrolled and classified into ≤4-year-old group（63 cases） and >4-year-old group（63 cases） based on the median age（4-year-old）. The general data were collected，and white blood cell（WBC） count，neutrophil percentage（NEUT%），C-reactive protein（CRP），D-dimer（DD），T-cell subsets [percentage of CD3⁺T cells（CD3⁺%），percentage of CD4⁺T cells（CD4⁺%），percentage of CD8⁺T cells（CD8⁺%） and the ratio of CD4⁺-to-CD8⁺（CD4⁺/CD8⁺ ratio）]，lactate dehydrogenase（LDH），IgA，IgG，IgM，interferon-gamma（IFN-γ），interleukin-6（IL-6） and interleukin-10（IL-10） were determined before and 7 d after treatment. Multivariate Logistic regression analysis was used to evaluate the relationship between various indicators and the disease outcomes of RMPP children. Results After treatment，the CD3⁺%，CD4⁺% and CD4⁺/CD8⁺ ratio in >4-year-old group were higher than those in ≤4-year-old group（P<0.05），while the levels of serum IgG，IgM，IFN-γ，IL-6，IL-10 and CD8⁺% were lower than those in ≤4-year-old group（P<0.05）. After adjusting for confounding factors（age，WBC count，NEUT%，CRP，IFN-γ，IL-6，IL-10），the CD4⁺/CD8⁺ ratio for 7 d after treatment was independently associated with the disease outcomes of RMPP children [odds ratio（OR）=0.63，95% confidence interval（CI） 0.45-0.84]. According to the median CD4⁺/CD8⁺ ratio（1.53） of RMPP children，those with a high CD4⁺/CD8⁺ ratio had a 26% lower risk of adverse outcome than those with a low CD4⁺/CD8⁺ ratio（OR=0.74）. When the CD4⁺/CD8⁺ ratio was divided into quintiles，the risk of adverse outcome in the Q2，Q3，Q4 and Q5 groups was reduced by 19%（OR=0.81），27%（OR=0.73），34%（OR=0.66） and 57%（OR=0.43），respectively，compared with the Q1 group. Compared with the NEUT% ≥54.76% group，the correlation between the CD4⁺/CD8⁺ ratio and disease outcomes was stronger in the NEUT% <54.76% group（P_interaction=0.013）. Conclusions Bronchoscopy can improve some cellular and humoral immune indicators in RMPP children. The CD4⁺/CD8⁺ ratio after treatment in RMPP children is related to disease outcomes，and a high CD4⁺/CD8⁺ ratio can reduce the risk of adverse outcome in RMPP children，especially in those with NEUT%≥54.76%.

Key words: T-cell subset, CD4⁺/CD8⁺ ratio, Refractory Mycoplasma pneumoniae pneumonia, Bronchoscopy, Children