Among the cells at the scene are macrophages and dendritic cells with Toll-like receptors on the surface. The receptors can instantly determine whether the foreign substance entering the body has the hallmarks of a major pathogen. If a pathogen presents itself—say, a noxious bacteria—not only does the immune system unleash a first-line attack but also the dendritic cells, now aware of the pathogen, begin their journey to find the T cell and B cell necessary to provide a more specific defense.
