Studies of microbiota have the potential to identify specific microbes or groups of microbes that may promote or mitigate intestinal inflammation owing to effects on the mucosal immune system.
Innate immune cells express receptors that detect microbial products or patterns, include granulocytes, macrophages, and dendritic cells.
Adaptive immune cells include B cells and T cells, which express variable receptors that recognize specific antigens, and mucosal-associated invariant T cells, which express antigen receptors with more limited diversity.
The mucosal immune system represents the largest component of the immune system, containing approximately 75% of all lymphocytes and producing the majority of immunoglobulin in healthy persons.
The mucosal immunity must balance the opposing demands of providing protective immunity against pathogens while preventing excessive immune responses against innocuous food antigens and commensal microbes.
Immune cells can be found in organized secondary lymphoid structures of the gut mucosa.
These gut-associated lymphoid tissues, as well as in intestinal draining mesenteric lymph nodes are embedded between surface epithelial cells, and within the underlying connective tissue.
Macrophages under the epithelium, kill invading microorganisms and dispose of pathogens and infected mucosal cells targeted by adaptive immune cells.
Innate lymphoid cells regulate tissue homeostasis, repair, remodeling, and microbial defense.
Subsets of these cells can be defined by their cytokine production.
Dendritic cells initiate and shape immune responses in mucosal tissues by acquiring antigen from microfold cells or by directly capturing and sampling luminal antigens, using membranous processes between epithelial cells.