Influence of macrophage activation on their capacity to bind bacterial antigens studied with atomic force microscopy

In this work we studied interactions between bacterial antigens and receptors on the surface of macrophages using atomic force microscopy (AFM). We used two bacterial cell wall components: lipopolysaccharide (LPS) derived from gram-negative Escherichia coli and exopolysaccharide (EPS) derived from gram-positive Lactobacillus rhamnosus. Interactions between these bacterial antigens and immune cell receptors were studied in peritoneal macrophages derived from two strains of mice, CBA and C3H/J, in which the Toll-like receptor 4 (TLR4) is genetically disabled. We collected 500 force-distance curves for LPS-activated cells using an EPS-covered AFM tip, and for EPS-activated cells using an LPS-covered AFM tip. Nonactivated cells were tested as reference cells. The results show that LPS-primed macrophages decrease their ability to bind EPS. Surprisingly, EPS-activated macrophages maintain or even increase their ability to bind LPS. This may suggest that in vivo commensal enteric bacteria, such as lactobacilli, will enhance the defense potential of local macrophages against pathogens expressing LPS.