Differential influence of Streptococcus mitis on host response to metals in reconstructed human skin and oral mucosa.

Lin Shang,Susan Gibbs,Sanne Roffel,Dongmei Deng

doi:10.1111/cod.13668

Abstract

BackgroundSkin and oral mucosa are continuously exposed to potential metal sensitizers while hosting abundant microbes, which may influence the host response to sensitizers. This host response may also be influenced by the route of exposure that is skin or oral mucosa, due to their different immune properties.ObjectiveDetermine how commensal Streptococcus mitis influences the host response to nickel sulfate (sensitizer) and titanium(IV) bis(ammonium lactato)dihydroxide (questionable sensitizer) in reconstructed human skin (RHS) and gingiva (RHG).MethodsRHS/RHG was exposed to nickel or titanium, in the presence or absence of S. mitis for 24 hours. Histology, cytokine secretion, and Toll‐like receptors (TLRs) expression were assessed.Results S. mitis increased interleukin (IL)‐6, CXCL8, CCL2, CCL5, and CCL20 secretion in RHS but not in RHG; co‐application with nickel further increased cytokine secretion. In contrast, titanium suppressed S. mitis–induced cytokine secretion in RHS and had no influence on RHG. S. mitis and metals differentially regulated TLR1 and TLR4 in RHS, and predominantly TLR4 in RHG.ConclusionCo‐exposure of S. mitis and nickel resulted in a more potent innate immune response in RHS than in RHG, whereas titanium remained inert. These results indicate the important influence of commensal microbes and the route of exposure on the host's response to metals.

Highlights

Skin and oral mucosa are continuously exposed to potential metal sensitizers while hosting abundant microbes, which may influence the host response to sensitizers
Co-exposure of S. mitis and nickel suppressed TLR4 protein levels, whereas co-exposure with titanium increased TLR4 expression. These results indicate that S. mitis and metal exposure are able to differentially regulate TLR1 and 4 expression in reconstructed human skin (RHS) and reconstructed human gingiva (RHG), with TLR1 and 4 being involved in RHS, and predominantly TLR4 being involved in RHG
The RHS and RHG models were compared throughout our study, since clinical experience indicates that skin exposure leads to sensitization, whereas oral mucosa exposure leads to tolerance,[3,4] with the reasons for this still being unknown

Summary

| MATERIALS AND METHODS

Human neonatal foreskin was obtained after informed consent from patients undergoing routine surgical procedures. After 24 hours exposure, the viability of the applied S. mitis (by CFU counting) and RHS/RHG (by MTT assay) was determined. The viability of RHS and RHG was measured by MTT assay as described previously.[50] In short, a 3 mm diameter biopsy was taken from each culture and incubated with MTT (Sigma, 2 mg/mL dissolved in phosphate-buffered saline [PBS]) overnight, and the absorbance was measured at 570 nm using a spectrophotometer (Mithras LB 940, Berthold Technologies, Bad Wildbad, Germany). The number of colony forming units (CFUs) of S. mitis at the time of exposure was determined by viable bacterial cell counting (CFU/mL): A sample was taken from the prepared S. mitis exposure, serial dilutions were made and plated on the brain hart infusion (BHI) agar plates, and colonies were counted after 96 hours of anaerobic incubation at 37C.

| RESULTS

Findings

| DISCUSSION