OBJECTIVEKawasaki disease (KD) is an acute febrile, multi-system endangeitis, which is mainly found in early childhood. Its etiology is still unknown. A great deal of clinical evidence and epidemiologic data suggest that KD is correlated with an acute immune dysfunction caused by infection. Many evidences in the past suggested that over-expression of proinflammatory cytokines, co-stimulatory molecules and chemokines, which were observed in KD, may contribute to the pathologic lesion of vascular endothelial cells. But the causative factors are still unknown. Toll-like receptor is a type I trans-membrane protein which could recognize ligands of pathogenic microbes, induce interferon beta (IFN-beta) and promote gene transcription of proinflammatory cytokines, co-stimulatory molecules and chemokines. This study was designed to investigate the role of MyD88-independent signal transduction of Toll-like receptor 4 in immunological pathogenesis of KD.

METHODSThirty-two children with KD and 16 age-matched healthy children were studied. Reverse-transcription PCR (RT-PCR) and real-time PCR were used to evaluate the mRNA levels of Toll-like receptor 4 and the molecules such as Toll-IL-1-receptor domain containing adaptor inducing IFN-beta (TRIF), TRIF-related adaptor molecule (TRAM), TANK-binding kinase 1 (TBK-1), IFN-beta, interferon-gamma-inducible protein 10 (IP-10), regulated on activation normal T cells expressed and secreted (RANTES), inducible nitric oxide synthase (iNOS) and suppressor of cytokine signaling 1 (SOCS-1) in monocytes/macrophages (MC), which participate in MyD88-independent signal transduction of toll-like receptors. Expression of costimulatory molecules such as CD40 in MC was analyzed by flow cytometry. Methylation-specific PCR was performed to analyze the methylation status of cytosine-phosphate-guanine (CpG) motif in SOCS-1 gene.

RESULTS(1) Compared with healthy controls, transcription levels of the molecules such as TLR4, TRIF, TRAM, TBK-1 and IFN-beta, were significantly up-regulated during acute phase of KD (P < 0.05), and down-regulated after treatment with intravenous immunoglobulin therapy. (2) Expression of iNOS and chemokines such as IP10 and RANTES in MC during acute phase of KD was remarkably elevated (P < 0.05), and down-regulated to some extents after treatment with intravenous immunoglobulin therapy. (3) Expression of costimulatory molecule CD40 in MC increased significantly during acute phase of KD [(6.19 +/- 2.25)% vs. (2.00 +/- 1.37)%, P < 0.05], while the protein levels of CD40 in KD-coronary artery lesion (CAL)(+) group was found to be significantly higher than that of KD-CAL-group [KD-CAL, (9.63 +/- 2.96)% vs. (4.12 +/- 1.91)%, P < 0.05]. (4) Expression levels of SOCS-1 mRNA were significantly up-regulated during acute phase of KD [(4.31 +/- 0.83) x 10(-3) vs. (1.09 +/- 0.23) x 10(-3), P < 0.05], and the levels of SOCS-1 gene in KD-CAL(+) group was found to be significantly lower than that of KD-CAL(-) group [(5.73 +/- 1.04) x 10(-3) vs (1.94 +/- 0.46) x 10(-3), P < 0.05]. (5) The CpG island of SOCS-1 DNA in KD patients was remarkably demethylated [(26.9 +/- 8.6)% vs (5.9 +/- 1.4)%, P < 0.05], and demethylation levels of SOCS-1 in KD-CAL(-) group were higher than that in KD-CAL+ group [(35.1 +/- 10.3)% vs. (13.2 +/- 3.7)%, P < 0.05].

CONCLUSIONAberrant activation of MyD88-independent pathways of Toll-like receptor 4 may be one of the factors causing disturbed immunological function in KD.