Lipopolysaccharide (LPS), one of the cell wall components of Gram-negative bacteria, is recognized by and interacted with receptors on macrophages. In this paper, we report the trapping of LPS-coated polystyrene particles via optical tweezers and measured its interaction with murine macrophages (J774A.1 cells) for cells pre-treated with extract of Reishi polysaccharides (EORP) vs. those without EORP treatment. Our experimental results indicate that the cellular affinity for LPS increases when the macrophage is pretreated with EORP. We demonstrate for the first time by conventional biological methods and by tracking the dynamics of optically-trapped LPS-coated particles interacting with J774A.1 cells, that EORP not only enhances J774A.1 cells surface expression of TLR4 and CD14, two receptors on macrophages, as well as LPS binding and phagocytosis internalization, but also reduces the adhesion time constant and increases the force constant of the binding interaction. The application of optical tweezers allows us to study the effect on a single cell quantitatively in real-time with a spatial resolution ~ 1 mum within a single cell.