Chemical communication between pathogens and host mucosal cells corresponds to a dynamic array of
molecular interactions. The signature molecules unique to microbial pathogens allow the mammalian immune
system to recognize them as a foreign element. This recognition is usually mediated by receptor proteins, which
can be classified as toll-like receptors, and recently described as nod-like receptors. These interactions result in
innate immune responses targeted against the invading organism. Pathogens also elaborate a variety of proteins
that actively engage host signaling pathways and subvert them to facilitate their growth and dispersal. The host
function alterations are mediated by microbial pathogens including inflammatory responses, secretory responses,
alteration of host cytoskeleton, disruption of epithelial tight junctions and apoptosis. Important interactions
between pathogens and host cell involves chemical signaling, that depends on cell density and signaling
molecules identified as autoinducers that function as hormone-like molecules in a phenomenon also known as
quorum sensing. Pathogens can use these systems to colonize and cause disease in the host, and we will further
discuss these mechanisms in this chapter. Chemical signaling involved in these interactions are potential targets
for therapeutic strategies against infectious microbes.