Leukocyte activation patterns in children with <i>Mycoplasma pneumoniae</i> infection: a comparison with viral and bacterial infections

Respiratory infections are a leading cause of pediatric emergency department (ED) visits, necessitating accurate pathogen identification. Flow cytometry markers, CD64 (nCD64) on neutrophils and CD169 (mCD169) on monocytes, are valuable in distinguishing bacterial from viral infections. However, their roles in identifying <i>Mycoplasma pneumoniae</i> (MP), an atypical bacterium, remain unclear. This prospective study analyzed 118 children with respiratory infections and fever, categorized into MP (<i>n</i> = 64), bacterial (<i>n</i> = 20), and viral (<i>n</i> = 33) groups, alongside 28 healthy controls. Viral infections showed elevated mCD169, while bacterial infections had increased nCD64. Notably, MP infections displayed significantly higher nCD64 and mCD169 levels compared to viral and bacterial groups. These markers effectively differentiated MP infections from other pathogens. MP-infected patients were further divided into DNA⁺IgM^-, DNA⁺IgM⁺, and DNA^-IgM⁺ subgroups. The DNA^-IgM⁺ group exhibited significantly lower nCD64 and mCD169 levels than the DNA⁺IgM⁺ group, with mCD169 also lower compared to the DNA⁺IgM^- group. These findings suggest dynamic marker changes during disease progression. In conclusion, leukocyte activation patterns, specifically nCD64 and mCD169, hold potential as diagnostic biomarkers for MP infections, aiding in distinguishing MP from other infections and improving triage and management in pediatric EDs.IMPORTANCERespiratory infections are one of the most frequent reasons children come to the emergency department, yet it is often difficult to quickly determine which pathogen is responsible. <i>Mycoplasma pneumoniae</i>, an atypical bacterium, is especially challenging to distinguish from common viral or bacterial infections, leading to delayed or inappropriate treatment. This study highlights the value of two immune cell markers, CD64 and CD169, measured by flow cytometry, in identifying infection patterns. We found that these markers not only distinguish bacterial from viral infections but also reveal a distinct signature in <i>Mycoplasma pneumoniae</i> cases. Moreover, marker levels appear to shift during different stages of illness, providing insights into disease progression. These findings suggest that CD64 and CD169 could become practical biomarkers to guide early diagnosis, treatment decisions, and patient triage in pediatric emergency settings, ultimately improving care for children with respiratory infections.