Substance P Modulates Toll-like Receptor-Mediated Activation Of Human Mast Cells

Abstract

RATIONALE: Substance P (SP) is a neuropeptide with potent neuroimmunoregulatory activity that may play a role in susceptibility to infection. We examined human mast cell responses to SP and toll-like receptors (TLR) ligands, pathogen-associated molecules that initiate innate immunity. METHODS: Human cultured mast cells (LAD2) were stimulated with SP or IgE/anti-IgE and expression of TLR was assessed by real-time PCR. LAD2 mast cells were activated by SP and TLR ligands including lipopolysaccharide (LPS; 100 ng/mL), Pam3CSK4 (10 ug/mL) and lipoteichoic acid (LTA; 10 ug/mL) and mast cell leukotriene and chemokine production was assessed by ELISA. Mast cell degranulation was determined by beta-hexosaminidase (beta-hex) assay. RESULTS: SP treatment of LAD2 upregulated mRNA for TLR2, 4 and 9 (3.4, 4.4 and 2.9 fold compared to untreated respectively, p < 0.01) while anti-IgE stimulation upregulated expression of TLR4 only (3.4 fold compared to untreated p < 0.01). Pretreatment of LAD2 with SP followed by stimulation with Pam3CSK4 or LTA potentiated production of LTC4 compared to treatment with Pam3CSK4 or LTA alone (2.6 and 2.1 fold over control respectively p < 0.01). Pam3CSK4, LPS and LTA did not induce LAD2 degranulation. Pretreatment with Pam3CSK followed by SP activation attenuated LAD2 degranulation compared to SP alone (36.4 + 1.3 vs. 44.0 + 2.9% beta-hex release, p < 0.01). Pretreatment with LTA or LPS followed by SP stimulation synergistically induced expression of CXCL8/IL-8 mRNA and production of CXCL8/IL-8 and CCL2/MCP-1 protein. CONCLUSIONS: We demonstrate that SP and TLR ligands regulate mast cell activation. These results suggest that neuronal responses may influence host defense responses and vice versa.