Children with atopic histories exhibit impaired lipopolysaccharide-induced Toll-like receptor-4 signalling in peripheral monocytes.

BACKGROUND: The hygiene hypothesis states that early exposure to bacterial products such as lipopolysaccharide (LPS) may be protective against the development of allergic diseases. Whether atopic disease affects the ability of immune cells to respond to LPS is unclear. Our laboratory has demonstrated previously that children express high levels of Toll-like receptor (TLR)-4 on CD4(+) cells in nasal mucosa. OBJECTIVE: To determine if children with a history of allergic disease have impaired responses to LPS on circulating CD4(+) leucocytes. METHODS: Peripheral blood mononuclear cells from children (aged 2-18) and adults with or without a history of atopic conditions were cultured with/without IL-4 or LPS for up to 24 h. Expression of surface TLR-4, CD14, CD4, CD3, as well as of intracellular phosphorylated (p42/p44) ERK and p38 mitogen-activated protein kinase (MAPK) were assessed by flow cytometry. RESULTS: A history of atopy in children was associated with impaired LPS-induced TLR-4-dependent phosphorylation of (p42/44) ERK and p38 MAPK by CD4(+) monocytes. Decreased LPS signalling was reproduced by pre-incubation of control cells with recombinant IL-4. LPS stimulation also decreased TLR-4 expression on monocytes from children without atopic histories but not from atopic subjects. CD4(+) T lymphocytes showed limited LPS responsiveness, regardless of atopic status. In contrast with non-atopic children, TLR-4 expression on monocytes of children with atopic histories decreased as a function of age. CONCLUSIONS: This study provides evidence for defective LPS recognition on circulating CD4(+) leucocytes of subjects with atopic histories compared with those from non-atopic children. CD4(+) TLR4(+) monocytes from children with atopic histories failed to phosphorylate MAPKs. Our results suggest that a history of atopic disease is associated with impaired TLR-4-mediated innate immune function compared with non-atopic children.

Epithelium-derived chemokines induce airway smooth muscle cell migration.

BACKGROUND: The remodelling of airway smooth muscle (ASM) associated with asthma severity may involve the migration of ASM cells towards the epithelium. However, little is known about the mechanisms of cell migration and the effect of epithelial-derived mediators on this process. OBJECTIVE: The main objective of the current study is to assess the effects of epithelial-derived chemokines on ASM cell migration. METHODS: Normal human ASM cells were incubated with supernatants from cells of the bronchial epithelial cell line BEAS-2B and normal human bronchial epithelial (NHBE) cells. To induce chemokine production, epithelial cells were treated with TNF-alpha. Chemokine expression by epithelial cells was evaluated by quantitative real-time PCR, ELISA and membrane antibody array. To identify the role of individual chemokines in ASM cell migration, we performed migration assays with a modified Boyden chamber using specific neutralizing antibodies to block chemokine effects. RESULTS: Supernatants from BEAS-2B cells treated with TNF-alpha increased ASM cell migration; migration was increased 1.6 and 2.5-fold by supernatant from BEAS-2B cells treated with 10 and 100 ng/mL TNF-alpha, respectively. Protein levels in supernatants and mRNA expression by BEAS-2B cells of regulated on activation, normal T cell expressed and secreted (RANTES) and IL-8 were significantly increased by 100 ng/mL TNF-alpha treatment. The incubation of supernatant with antibodies to RANTES or IL-8 significantly reduced ASM cell migration, and the combined antibodies further inhibited the cell migration. The migratory effects of supernatants and inhibiting effects of RANTES and/or IL-8 were confirmed also using NHBE cells. CONCLUSION: The results show that chemokines from airway epithelial cells cause ASM cell migration and might potentially play a role in the process of airway remodelling in asthma.