Novel tools for modulating immune responses in the host-polysaccharides from the capsule of commensal bacteria.

The intestinal microflora of mammals includes organisms with many unique molecules that enable them to modulate their immediate environment and thus to survive and reside successfully in the gut. Little is known about how individual molecules from these microbes affect the host's health and development, but the microbiome is considered a crucial factor in intestinal homeostasis. The literature highlights numerous ways in which the microflora stimulates the mammalian host's immune system, starting with its development and continuing to the initiation and resolution of inflammation. The influence of the microflora on the host's immune system is mediated principally by interactions with various antigen-presenting cells of the gut; these interactions result in substantial modulation of both the innate and the adaptive arms of the immune system. Certain polysaccharide antigens from the capsules of some commensal bacteria represent a functional class of molecules that exert profound immunomodulatory effects. Because of their unique structural features, including a zwitterionic charge motif, these polysaccharides can participate to a significant extent in the orchestration of host immune homeostasis. These molecules can be used to elucidate the basic biology of the mammalian intestine and have the potential for use in novel therapeutic regimens for various systemic or intestinal pathological conditions.