Increased TLR2 and TLR4 Expression in Peripheral Neutrophils Isolated from Kawasaki Disease

Background: Since neutrophils are important in innate immunity against invading microorganisms, this study investigated the expression of TLR2 and TLR4 in neutrophils derived from infants and children aged 12 years or younger as a marker of such immune functions. Methods: We enrolled 70 patients aged 12 years or younger: 18 patients with microbial infections, 14 patients with Kawasaki disease (KD), and 38 patients without infection, who first presented to the pediatric department at Toho University Omori Medical Center, Tokyo, Japan. The expression of TLR2 and TLR4 in neutrophils was assayed by flow cytometry, using phycoerythrin-conjugated antihuman monoclonal TLR2 or TLR4. Results: TLR2 and TLR4 expression in neutrophils derived from patients aged 1-5 years old without infection were significantly higher than in patients younger than 1 year and 6 years or older. In addition, TLR2 expression was greater than TLR4 expression in patients aged 12 years or younger with and without infections. The coefficients between expression of TLR2 and TLR4 in patients with and without infections were 0.8730 and 0.8393 respectively. Similar findings were obtained in patients with KD, and the coefficient was 0.9095. C-reactive protein (CRP) serum concentration and TLR2 and TLR4 expression in neutrophils gradually decreased during the follow-up period in patients with KD. Conclusions: The function of neutrophils matured between the ages of 1 and 5 years. The pattern of decrease in CRP levels was correlated to levels of toll-like receptors (TLRs) expression, especially TLR2, in KD.