Mucosa-Associated
Lymphoid Tissue
The mucosal lining of the alimentary canal and
airways is in many ways specialised to facilitate the exchange of substances
between the external environment and the body. Unfortunately, these
specialisation do not just apply e.g. to components of the digested food but
also pathogens. This is combined with excellent living conditions for bacteria
in parts of the alimentary canal - in particular the ileum and the colon.
Lymphoid tissue located beneath the mucosal epithelia, mucosa-associated lymphoid tissue (MALT), protects the body against pathogens that
may enter the body via the mucosa. The importance of this task is reflected in
the mass of the MALT, which corresponds to the combined mass of the other
lymphoid organs and tissues.
The task that the immune cells of the MALT have to
accomplish is different from that of other parts of the immune system. We do
need a defense against pathogens, but it would not be a good idea to mount an
immune response against components of the food. Immune cell activation therefore
differs between the MALT and other lymphoid tissues.
This difference is mediated by different receptors
expressed by immune cells of the MALT and by different substances which they
release upon contact with an antigen. Because of their specific functions,
immune cells of the MALT do not mingle with other immune cells. Epithelial
cells of the vessels supplying the MALT express specific receptor which are
recognized by MALT immune cells and allow their homing to the MALT during
recirculation. Lastly, MALT plasma cells produce a secretable form of
antibodies, immunoglobulin type A dimers, which can be taken up by epithelial
cells and then released onto the epithelial surface.
Specialisation of MALT immune cells occur at the molecular level. In routine
histological preparations, immune cells of the MALT look pretty much like
immune cells of other lymphoid tissues.
Often MALT consists of small accumulations of
lymphoid cells or one to a few lymph follicles beneath the epithelium and
possibly extending into the submucosa. The tonsils
and Peyer's patches are large accumulations of
lymphoid tissue with associated specialisations of the epithelium.
![thumbnail]( "Mucosa-Associated Lymphoid Tissue")
Title:
Mucosa-Associated Lymphoid Tissue
by:
om
at
2013-02-15T03:28:00+07:00
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Mucosa-Associated Lymphoid Tissue