OBJECTIVEAcute respiratory distress syndrome (ARDS) is usually diagnosed on the basis of clinical manifestations. However, a sensitive and effective biochemical index is important for early diagnosis of ARDS. It has been confirmed that macrophage migration inhibitory factor (MIF) expression is increased in patients with ARDS (adults and children). The present study aimed to investigate the expression and pathogenic role of MIF in children with ARDS by determining the serum level of MIF and expression of MIF in lung tissues.

METHODSTotally 18 children with ARDS, who were diagnosed in the department of pediatrics, the People's Hospital of Nanhai District, and 8 healthy children (control) were enrolled into the study. The serum level of MIF in ARDS children and normal children were measured by using enzyme-linked immunosorbent assay (ELISA). Peripheral blood mononuclear cell (PBMC) MIF expression was determined by flow-cytometry. The expression of MIF mRNA and protein in lung tissues were detected by using double-staining immunohistochemistry and in situ hybridization.

RESULTS(1) The serum level of MIF and PBMC MIF expression were (2040 +/- 146) microg/L and (8.98 +/- 2.76)%, respectively in ARDS children, which were significantly higher than those in the healthy children [(53 +/- 31) microg/L and (0.97 +/- 0.28)%, (P < 0.01)]. (2) In situ hybridization and immunohistochemistry showed that the number of KP(1)(+) cells and the percentages of MIF(+) expressed cells and MIF mRNA expressed cells were (229 +/- 87)/mm(2), (31.4 +/- 7.8)% and (34.71 +/- 8.91)%, respectively in the bronchoalveolar lavage fluid of ARDS children, which were significantly higher than those in the healthy children [(11 +/- 6)/mm(2), (1.9 +/- 0.8)% and (1.17 +/- 0.16)%, P < 0.01)]. (3) The number of KP(1)(+) cells and the percentages of MIF(+) expressed cells and MIF mRNA expressed cells were (319 +/- 129)/mm(2), (41.7 +/- 11.6)% and (45.13 +/- 13.2)% in ARDS lungs interstitium, which were significantly higher than those in the healthy children [(11 +/- 6)/mm(2), (1.9 +/- 0.8)% and (1.40 +/- 0.25)%, (P < 0.01)].

CONCLUSIONSThe level of MIF increased in serum and lung interstitium in ARDS children. Macrophage infiltration was demonstrated in lung interstitium and bronchoalveolar lavage fluid of ARDS children, MIF was expressed and significantly associated with the number of macrophage, which suggest that MIF plays an important role in the pathogenesis of ARDS. The level of MIF expression and macrophage infiltration can be regarded as a sensitive and effective biochemical index in the early diagnosis of ARDS.