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.
Secondary lymphoid organs
- 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 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 the myriads 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.
In patients with haemochromatosis the reticuloendothelial system is a site of iron acumulation.
Lymphoma of the reticuloendothelial system is called reticuloendotheliosis.