The
reticuloendothelial system (
RES), part of the
immune system, consists of the
phagocytic cells located in
reticular connective tissue, primarily
monocytes and
macrophages. These cells accumulate in
lymph nodes and the
spleen. The
Kupffer cells of the
liver and tissue
histiocytes are also part of the RES.
Mononuclear phagocytic system and lymphoreticular system are synonymous with RES.
The reticuloendothelial system is divided into primary and secondary lymphoid organs.
Primary lymphoid organs
Primary (or
"central") lymphoid organs - the sites where the cells of the RES are
produced. The cells of the RES are produced in the
bone marrow.
The thymus is also included as it is the required site for T cell maturation.
Secondary lymphoid organs
Secondary (or
"peripheral") lymphoid organs - the sites where the cells of the RES
function. This includes the
lymph nodes,
tonsils, spleen, and "MALT" (
mucosa-associated lymphoid tissue).
- MALT is further divided into the "GALT" (gut-associated lymphoid tissue) and the "BALT" (bronchus-associated lymphoid tissue).
- The Kupffer cells of the liver act as part of this system but are not organized into a tissue; rather, they are dispersed throughout the liver sinusoids.
- The microglia of the Central Nervous System (CNS) can be considered a part of the reticuloendoethelial system. They are scavenger cells that proliferate in response to CNS injury.
Function
The secondary lymphoid structures function to survey all entering or circulating antigen and to mobilize an immune response against foreign antigen upon its discovery. The GALT and BALT are privy to a myriad of antigen entering the gastrointestinal and respiratory tracts, respectively. All extracellular fluid must filter through lymph nodes as it traverses the lymphatics on its way back to the systemic circulation. Antigen residing in the interstitium is thus swept to the lymph nodes for processing.
Finally, the spleen filters the blood in search of antigen. Upon the discovery of foreign antigen, all of these tissues react in a similar manner to amass an appropriate and multifaceted immune response.
Clinical significance
Lymphoma of the reticuloendothelial system is called reticuloendotheliosis.
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