Background : Mycoplasma pneumoniae pneumonia (MPP) is a common respiratory illness in children, particularly those with allergic constitutions. NK cells and cytokines are thought to be involved; however, understanding of the immunopathology of MPP is incomplete.
Methods : Peripheral blood samples were collected from 51 children hospitalized with with MPP, 26 with an allergic constitution and 25 without, and 29 healthy controls. NK cell subsets were analyzed by flow cytometry and the expression of interleukin (IL)-1 alpha and IL-18 was detected by ELISA. The relationship between NK cell subsets and the expression of IL-18 and IL-1 alpha was determined.
Results : The number of CD3 − CD56 + NK cells and CD3 − CD56 dim CD16 bright NK cells in children with MPP was lower than in healthy controls (P < 0.05). The percentage of CD3 − CD56 + NK cells, CD3 − CD56 dim CD16 bright NK cells and the number of CD3 − CD56 dim CD16 bright NK cells in the MPP allergic group were lower than in the non-allergic group (P < 0.05). The expression of IL-18 was significantly increased in the MPP groups (P < 0.05), and the absolute number of CD3 − CD56 dim CD16 bright NK cells negatively correlated with IL-18 levels in the peripheral blood (P < 0.05).
Conclusion : Reduced numbers of NK cell subsets were identified in children with MPP and MPP with an allergic predisposition compared with healthy controls. Concomitant increases in IL-18 in children with MPP suggest the involvement of IL-18 in the immunopathogenesis of MPP and may be related to the reduced CD3 − CD56 dim CD16 bright NK cells.
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