Binding of CD14 to Mycoplasma genitalium-Derived Lipid-Associated Membrane Proteins Upregulates TNF-α

Abstract

Lipid-associated membrane proteins (LAMPs) are a mixture of mycoplasmal lipoproteins expressed on the surface, and they are the main structures for interaction with the host cells. The objective of this study was to explore the role of CD14 in immune recognition of Mycoplasma genitalium-derived LAMPs and investigate whether the binding of CD14 to LAMPs affects the inflammatory response. Enzyme-linked immunosorbent assay (ELISA), transient co-transfection, dual-luciferase reporter assay, specific inhibition assay, and competitive inhibition ELISA (CI-ELISA) were used. CD14 was involved in LAMP-stimulated production of tumor necrosis factor (TNF)-α by blocking CD14 antibody in THP-1 cells. Co-transfection experiments in HeLa cells provide evidence that CD14 facilitates LAMP-induced TNF-α release via toll-like receptor 2 (TLR2). In addition, LAMP-induced TNF-α release was increased by soluble CD14 but decreased by soluble TLR2. Lipid moieties of LAMPs pre-treated with lipoprotein lipase were responsible for TNF-α production. The binding of CD14 to LAMPs was supported by binding assay and CI-ELISA. Thus, we provide evidences that CD14 is not only able to recognize LAMPs but also its binding to LAMPs upregulates TNF-α release. These findings provide insight into the function of CD14 and the pathogenesis of mycoplasmal infections.