Analysis of signaling pathways involved in peptidoglycan-induced RANTES production from murine Langerhans cells

Our previous study showed that percutaneous application of peptidoglycan from Staphylococcus aureus induced eosinophil infiltration in murine skin through production of CCL5/RANTES (regulated upon activation in normal T cells expressed and secreted) from epidermal Langerhans cells. Although it is well known that peptidoglycan is an agonist of Toll-like receptor (TLR)-2, it is unclear whether other TLR agonists are able to induce RANTES production from Langerhans cells.

Langerhans cells were purified from murine epidermal cells by the panning method using anti-IA(d) monoclonal antibody. RANTES production by Langerhans cells was investigated by RT-PCR and ELISA. Analysis of the signaling pathways responsible for RANTES production by Langerhans cells was performed by ELISA using N-acetyl-L-cysteine, SP600125, SB203580 and PD98059, which are specific inhibitors of NF-kappaB activation, JNK, p38 MAPK and ERK, respectively, and was finally confirmed by Western blot analysis.

Peptidoglycan, poly(I:C), lipopolysaccharide and CpG DNA, which signal through TLR-2, TLR-3, TLR-4 and TLR-9, respectively, were found to strongly induce RANTES production. Treatment with N-acetyl-L-cysteine inhibited all TLR agonist-induced RANTES production. However, treatment with SP600125 did not inhibit CpG DNA-induced RANTES production. Furthermore, treatment with SB203580 inhibited only peptidoglycan- and lipopolysaccharide-induced RANTES production and the inhibition was correlated with that of p38 MAPK phosphorylation.

These results suggest that the signaling pathway of RANTES production from murine Langerhans cells induced by different TLR stimuli is not necessarily the same, and that inhibition of p38 MAPK may be a more specific therapeutic target for eosinophilic inflammation in patients with atopic dermatitis associated with S. aureus colonization.