host-pathogen interface

In cellular biology, the host-pathogen interface refers to the exchange of biochemical signals that occurs when a microbe encounters its host or target cell. Such cross-talk between the two can result in either a symbiotic or hostile cross-fire. In certain locations, such as the gastro-intestinal tract, the animal host's intestinal mucous-lining on the host-cell external surface may prevent a food-poisoning pathogen from achieving physical adhesion to the plasma membrane of the host cell. In addition, the arsenal of anti-microbial peptides and defensins secreted by the host can damage the integrity of the approaching microbial pathogens. Innate and cellular immunity of the animal host may also neutralize the pathogens before they come in close contact with specific host or target cells. Gram-negative bacterial pathogens having an additional outer membrane consisting largely of endotoxic lipopolysaccharide (LPS), membrane-pore forming porins, and some other outer membrane proteins, providing an apparent advantage compared to Gram-positive microbes, which lack outer membrane. Thus Gram-negative organisms have an additional storage compartment called a periplasm, a cellular space between bacterial outer membrane and the inner membrane. The periplasm allows special attributes to the Gram negative organisms, as this compartment can expand to accommodate increasing amounts of microbial secretions; it can also bleb out nanovesicles, called bacterial outer membrane vesicles, (OMVs). These OMVs can translocate a variety of biochemical signal molecules to other target cells of its own type (intra-species) for quorum sensing or other competing microbes (inter-species) to thwart them from sharing the same nutritional niche, or to animal/plant eukaryotic cells for inter-kingdom interactions. OMVs thus open a new vista in the important field of membrane vesicle trafficking. This was heralded as a revolutionary process of vesicular exocytosis in prokaryotes for multiple purposes, including invasion of animal hosts, and inter-bacterial interactions.