Asplenia overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Anum Dilip, M.B.B.S[2]
Overview
Hippocrates made the first description of the gross anatomy of the spleen in 421 BC. In 1899, Chauffard described that increased splenic activity is linked to hemolysis, and in 1910, Sutherland and Brughard performed the first therapeutic splenectomy in a patient with hereditary spherocytosis. In 1919, Morris and Bullock provided initial experimental evidence of the protective role of the spleen against infections. Asplenia may be classified into two groups based on its cause: Congenital: Isolated asplenia, heterotaxy syndrome, and Acquired: Functional asplenia. The spleen consists of three functional inter-related compartments: red pulp, white pulp, marginal zone. The primary physiologic role of spleen is the filtration and processing of senescent blood cells, predominantly red blood cells and immunologically helps protect against encapsulated microorganisms and response to infectious pathogens. It contains both hematopoietic and lymphopoietic elements, which provides a basis for extramedullary hematopoiesis when necessary. The spleen plays integral roles in the immune system and reticuloendothelial systems. It also modulates the inflammatory and coagulation cascades. Asplenia can refer to an anatomic absence of the spleen or functional asplenia secondary to a variety of disease states. The absence of a spleen is a well-known risk factor for severe bacterial infections, especially due to encapsulated bacteria. The spleen contains 2 types of tissues: white pulp and red pulp. The white pulp is rich in T-cell lymphocytes, naïve B-cell lymphocytes, and macrophages. The antigen-presenting cells (APC) can enter the white pulp and activate T cells, which in turn activate naïve B cells and differentiate into plasma cells that generate immunoglobulin M antibodies followed by immunoglobulin G antibodies. B cells can also act as antigen-presenting cells and has a phagocytic function to help opsonize encapsulated bacteria. About half of the total B cells in the blood express the memory marker CD27 and carry somatic mutations, and are therefore thought to be memory B cells. There are two types of memory B cells in human beings: switched memory B cells and IgM memory B cells. Switched memory B cells, which are the final product of germinal center reactions, produce high-affinity antibodies and have a protective function against infection. IgM memory B cells, need the spleen for their survival and generation and have the ability to produce natural antibodies. They also produce antibodies against Streptococcus pneumonia, Neisseria meningitidis, and Haemophilus influenzae type b. The red pulp has macrophages and is responsible for filtering damaged, older red blood cells as well as phagocytosing opsonized bacteria. Due to this role of removing damaged erythrocytes, the spleen also plays an important role in the defense against intraerythrocytic parasitic infections such as malaria and Babesia. Functional asplenia is associated with sickle cell anemia, hemoglobin sickle cell disease, and sickle cell hemoglobin β thalassemia. Patient with these hemoglobinopathies starts losing a splenic function, where the spleen is initially enlarged due to excessive red cell entrapment results in atrophy and degeneration in advanced disease. This atrophy is called autosplenectomy and may be consequent] to multiple acute episodes of entrapment of massive red cell volumes in the splenic tissue, followed by splenic infarctions. Genes involved in the pathogenesis of Isolatd congenital asplenia include: Mutations in RPSA exons can affect the translated or untranslated regions and can underlie Isolatd congenital asplenia(ICA) with complete or incomplete penetrance. Asplenia is caused by either congenital, acquired conditions, or functional. Common cause include: Acquired asplenia associated after trauma or surgery, is one of the commonest cause of the absence of splenic tissue, Functional asplenia include diseases such as sickle cell (SC) disease, hemoglobin SC disease and sickle beta-thalassemia, Hyposplenia occurs due to medical conditions such as chronic liver disease, human immunodeficiency syndrome (HIV), malignancies, thalassemia, celiac disease, ulcerative colitis, sarcoidosis, amyloidosis, lupus, rheumatoid arthritis. Less Common Causes include: Congenital asplenia may be isolated or usually seen as a clinical syndrome such as ivemark syndrome.
Historical Perspective
Hippocrates made the first description of the gross anatomy of the spleen in 421 BC. In 1899, Chauffard described that increased splenic activity is linked to hemolysis, and in 1910, Sutherland and Brughard performed the first therapeutic splenectomy in a patient with hereditary spherocytosis. In 1919, Morris and Bullock provided initial experimental evidence of the protective role of the spleen against infections.
Classification
Asplenia may be classified into two groups based on its cause: Congenital: Isolated asplenia, heterotaxy syndrome, and Acquired: Functional asplenia.
Pathophysiology
The spleen consists of three functional inter-related compartments: red pulp, white pulp, marginal zone. The primary physiologic role of spleen is the filtration and processing of senescent blood cells, predominantly red blood cells and immunologically helps protect against encapsulated microorganisms and response to infectious pathogens. It contains both hematopoietic and lymphopoietic elements, which provides a basis for extramedullary hematopoiesis when necessary. The spleen plays integral roles in the immune system and reticuloendothelial systems. It also modulates the inflammatory and coagulation cascades. Asplenia can refer to an anatomic absence of the spleen or functional asplenia secondary to a variety of disease states. The absence of a spleen is a well-known risk factor for severe bacterial infections, especially due to encapsulated bacteria. The spleen contains 2 types of tissues: white pulp and red pulp. The white pulp is rich in T-cell lymphocytes, naïve B-cell lymphocytes, and macrophages. The antigen-presenting cells (APC) can enter the white pulp and activate T cells, which in turn activate naïve B cells and differentiate into plasma cells that generate immunoglobulin M antibodies followed by immunoglobulin G antibodies. B cells can also act as antigen-presenting cells and has a phagocytic function to help opsonize encapsulated bacteria. About half of the total B cells in the blood express the memory marker CD27 and carry somatic mutations, and are therefore thought to be memory B cells. There are two types of memory B cells in human beings: switched memory B cells and IgM memory B cells. Switched memory B cells, which are the final product of germinal center reactions, produce high-affinity antibodies and have a protective function against infection. IgM memory B cells, need the spleen for their survival and generation and have the ability to produce natural antibodies. They also produce antibodies against Streptococcus pneumonia, Neisseria meningitidis, and Haemophilus influenzae type b. The red pulp has macrophages and is responsible for filtering damaged, older red blood cells as well as phagocytosing opsonized bacteria. Due to this role of removing damaged erythrocytes, the spleen also plays an important role in the defense against intraerythrocytic parasitic infections such as malaria and Babesia. Functional asplenia is associated with sickle cell anemia, hemoglobin sickle cell disease, and sickle cell hemoglobin β thalassemia. Patient with these hemoglobinopathies starts losing a splenic function, where the spleen is initially enlarged due to excessive red cell entrapment results in atrophy and degeneration in advanced disease. This atrophy is called autosplenectomy and may be consequent] to multiple acute episodes of entrapment of massive red cell volumes in the splenic tissue, followed by splenic infarctions. Genes involved in the pathogenesis of Isolatd congenital asplenia include: Mutations in RPSA exons can affect the translated or untranslated regions and can underlie Isolatd congenital asplenia(ICA) with complete or incomplete penetrance.
Causes
Asplenia is caused by either congenital, acquired conditions, or functional. Common cause include: Acquired asplenia associated after trauma or surgery, is one of the commonest cause of the absence of splenic tissue, Functional asplenia include diseases such as sickle cell (SC) disease, hemoglobin SC disease and sickle beta-thalassemia, Hyposplenia occurs due to medical conditions such as chronic liver disease, human immunodeficiency syndrome (HIV), malignancies, thalassemia, celiac disease, ulcerative colitis, sarcoidosis, amyloidosis, lupus, rheumatoid arthritis. Less Common Causes include: Congenital asplenia may be isolated or usually seen as a clinical syndrome such as ivemark syndrome.
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