Fish Immunology (1+1)

Unit 5- Specific defence mechanism in Fish

5.2.3. Secondary lymphoid organs
Secondary lymphoid organs contains kidney, spleen, mucosa.
Kidney
The head kidney which also works as secondary lymphoid organ is important in mounting immune response. The head kidney is a major organ where antibody producing cells are formed. The presence of monocytes, macrophages and neutrophils and the lack of lymphocytes in the early life of many fish species indicate the importance of innate immune system during early stage of life. The mature kidney in Indian major carp contains mostly lymphocytes besides other blood cells.
Spleen
Spleen is the secondary lymphoid organ and it is the last organ to form during the development of the lymphoid organs in teleosts. In most teleosts, the spleen is present as an encapsulated organ with abundant red pulp and poorly developed white pulp but in majority of the teleosts these pulp are not clearly distinct. The red pulp occupies most of the space in spleen and contains lymphocytes and macrophages. The white pulp occupies less space and contains poorly developed ellipsoids and numerous melano-macrophage aggregations. Ellipsoids purifying the blood by trapping immunocomplexes and later digested by the macrophages.
Mucosa
Mucosa is highly diffused and unorganized lymphoid tissue that consists of granulocytes, macrophages in the gut, gills and skin. These lymphoid tissue occur mainly under the epithelial cells of the gut and in lamina propria. Macrophages and sIg+ lymphocytes also present in the mucosal lymphoid tissues