Monocyte subsets study in children with Mycoplasma pneumoniae pneumonia

The aim of this study was to evaluate the changes in the three subsets of monocyte (classical, intermediate, and non-classical) and the expression of human leukocyte antigen-DR (HLA-DR) on monocyte subsets during MP pneumonia in children. Monocyte subsets were analyzed in the peripheral blood of healthy volunteers and MP pneumonia patients at the stages of admission and remission after clinical therapy. They were defined as classical (CD14⁺CD16^-), intermediate (CD14^brightCD16⁺), and non-classical (CD14^dimCD16⁺) using flow cytometry. Furthermore, three subsets of monocyte were analyzed for the expression of HLA-DR. Patients with MP pneumonia at admission had a higher proportion of intermediate and non-classical monocytes than healthy subjects (all P < 0.05). The proportion of intermediate subset and non-classical subset was lower in MP pneumonia patients at remission than at admission (all P < 0.05). In comparison with the other monocyte subsets, intermediate subset showed a significantly higher percentage of HLA-DR in MP pneumonia patients at admission (P < 0.05). Further analysis revealed that the expression of HLA-DR on intermediate subset was lower in severe patients than in non-severe patients (P < 0.05).Our data has shown for the first time that MP pneumonia is associated with the increased proportion of non-classical and intermediate monocytes, indicating the involvement of monocyte-related mechanisms in the pathogenesis of this disease. Additionally, the decreased expression of HLA-DR on CD14^brightCD16⁺ subset may be a potential indicator of the severity of MP pneumonia.