Abstract: Objective? To analyze the characteristics of cytokines in bronchoalveolar lavage fluid (BALF) of Mycoplasma pneumoniae pneumonia (MPP) patients and its influence factors and correlations with biochemical index in peripheral blood. Method The clinical data of 122 children with MPP who underwent bronchoscopy were retrospectively analyzed, and the indicators and cytokines were compared between groups. Results In the MPP children ( 62 boys and 60 girls) aged 4 years old ( 1 to 14 years) on average, severe MPP was found in 37 patients. In BALF, two cytokines that were elevated most were IL-6 and TNF-α. The levels of IL- 6 , TNF - α, IL- 10 , and IFN-γ in BALF were significantly different between fever group and non-fever group, between persistent fever group, and fever regression group, and between azithromycin effective and ineffective groups (P< 0. 05 ). The levels of IL- 6, TNF-α, IFN-γ, and IL- 17 A in severe MPP group were significantly higher than those in mild MPP group. The levels of TNF-α, IL- 10 , and IFN-γ in high load group were significantly higher than those in low load group. The levels of IL- 6 and TNF-α in lung consolidation group were significantly higher than those in lung patch shadow group (all P<0. 05 ). There were positive correlations between levels of D-dimer and cytokines IL- 6, IL- 10, IFN - γ, and TNF-α in BALF of MPP children (r= 0 . 323 ~ 0 . 452 , P< 0 . 001 ). Peripheral blood lactate dehydrogenase (LDH) level was positively correlated with IL- 6 , TNF-α, and IFN-γ levels in BALF (r=0.229~0.347, P< 0 . 01 ). The serum albumin level was negatively correlated with levels of cytokines IL- 6 , IL- 10 , TNF- α, and IFN - γ in BALF (r=-0 . 260 ~-0 . 214 , P< 0 . 05 ). Conclusion? Local inflammatory response in MPP children is dominated by IL- 6 and TNF-α. The severity of MPP, the presence of fever, persistent fever during bronchoscopy, MP load, and types of pulmonary lesions and the therapeutic effect of azithromycin all affect the levels of BALF cytokines. D-dimer, LDH and albumin in peripheral blood of MPP children are correlated with BALF cytokines and they play certain roles in guidance for the assessment of lung inflammation.

Key words: Mycoplasma pneumoniae pneumonia;? bronchoalveolar lavage fluid;? cytokine;? child