During the course of an infectious disease, most microbial pathogens interact with host tissues in some fashion. This interaction can be of a direct nature, by binding receptors found on host cells, or by binding secreted components that may either immobilize the microorganism at an extracellular site or promote adhesion to host cells. The ultimate site of localization during the infection of the microorganism is most probably determined by the particular array of surface molecules found on the microbial cell surface. 1 An internal or external localization of the microorganism relative to host cells is in large part determined by the particular receptors to which microbial surface components bind. 2 Furthermore, there is some evidence that the survival of a microorganism within a particular cell type may depend on the particular receptor bound. 3 , 4