To investigate the expression profile of novel immunomodulatory factor interleukin (IL)-41 in pediatric patients with Mycoplasma pneumoniae pneumonia (MPP), and to analyze its correlation with disease severity, diagnostic efficacy and value for predicting severe progression.

Total of 32 children with MPP under 18 years old, admitted to Beijing Friendship Hospital, Capital Medical University and Hebei Yiling Hospital throughout 2024 were enrolled for retrospective cohort study, including 17 cases of mild disease (mild group) and 15 cases of severe disease (severe group), while 8 healthy children undergoing physical examinations were selected as the control group. Serum IL-41 level was detected in enrolled children by enzyme-linked immunosorbent assay (ELISA), and parameters such as gender, age, C-reactive protein (CRP), procalcitoninand (PCT) and IL-6 levels were compared, respectively. The diagnostic efficacy of these markers for severe MPP was evaluated by receiver operating characteristic (ROC) curve, the relationships between serum IL-41 level and clinical indicators were analyzed by correlation heatmaps.

Among the 32 enrolled ediatric patients with MPP, there were 11 males (34.4%) and 21 females (65.6%), with a mean age of (8.60±2.89) years old. There was no statistically significant difference in age between mild group and severe group [(9.06±3.45) years old vs. (8.07±2.09) years old] (t=0.393, P=0.697). IL-41 level of MPP children in mild group was significantly higher than that of healthy control group [(182.191±65.364) pg/ml vs. (137.628±2.914) pg/ml], with significant difference (t=2.805, P=0.013). But there were no significant difference of IL-41 level between severe group and healthy control group, or between mild group and severe group (all P>0.05). The area under the ROC curve (AUC) for diagnostic differentiation between mild group and severe group by individual biomarkers IL-41, CRP and IL-6 were 0.652, 0.590 and 0.522, respectively, all showing suboptimal performance. However, the three idicators combined AUC significantly improved to 0.768 (95%CI: 0.598-0.938, P=0.013), with the sensitivity and specificity of 93.8% and 57.1%, respectively. In mild group, the IL-41/CRP ratio [24.47 (7.4, 41.1)] and IL-41/IL-6 ratio [26.88 (9.1, 34.6)] were significantly higher than those of severe group [10.81 (1.3, 18.9) and 9.85 (1.7, 15.1)], with significant differences (Z=－3.946 and －1.957, both P<0.001). Spearman correlation analysis demonstrated a significant positive correlation between serum IL-41 and IL-6 levels of patients with MPP (r=0.64, P=0.020).

Serum IL-41 level is significantly elevated in children with mild MPP, which was elevated but without significance in severe MPP cases, suggesting that IL-41 may exert a protective effect against severe disease as an anti-inflammatory factor. Combined detection of IL-41, CRP and IL-6 enhances the diagnostic accuracy for severe MPP, and dynamic monitoring of IL-41 level may aid in disease progression assessment of patients with MPP.