B CELLS DEFINITION

B CELLS DEFINITION

B cells are the defender cells of our body which produce antibodies to protect us from diseases and infections. They then enter the blood and circulate through our bodies. The basic function of B cells is to produce antibodies in response to foreign proteins such as viruses, bacteria and tumor cells. Each is specific to a particular site on an antigen. B cells are derived from bone marrow and then develop into plasma. These cells not only fight infection but also generate memory cells, which help in recognizing specific invaders and launch an attack against them if they are encountered again. B cells act as the defending army of the human immune system providing a shield against several diseases and viruses. These cells, present in the spleen, help to produce antibodies that destroy old red blood cells.

Receptor-mediated endocytosis is a process in which antigen molecules are engulfed by the B cells. This process in initiated when B cell receptor (BCR) bind to a particular bacterial antigen. During this process, these antigens are broken down into peptide fragments and are then displayed at the surface of a molecule known as Class II MHC.

When B cells encounter their antigens and receive an additional signal from T cells, they further differentiate into two types of B cells i.e. Plasma B cells and Memory B cells. Whenever an antigen is T- dependent, T cell help is required for antibody production and the signal for activation comes from B cell receptor (BCR) and Th2 cell. There are some antigens which are T cell independent and they deliver the antigen as well as the second signal to the B cells. B cells will not produce antibodies unless they are activated.

B cells function

The basic function of B cells is to produce antibodies to protect the body against foreign invaders such as viruses, bacteria and tumor cells. B cells help our body to withstand damage from anti-biotic resistant bacteria and prevent the reoccurrence of pathogens hiding in the body like herpes that causes cold sores and mycobacterium that causes tuberculosis.

Another primary role of B cells is to produce antigens and perform the vital role of antigen presenting cells (APC’s). When B cells get activated they develop into memory cells by interacting with the antigens.

B cells receptor (BCR)

B cells receptor or BCR is a unique receptor protein which is present on the surface of each B cell that binds to the specific antigen. B cells are not thymus dependent but are responsible for the production of immunoglobin and express immunoglobin on their surface. The foreign antigens circulating in the bloodstream are destroyed by the antibodies produced by the B cells. Generally each B cell produces one specific antibody and when it gets activated by an antigen, it produces large cells known as plasma cells which produce antibodies.

B cells also play a vital role in maintaining immune tolerance because it prevents the immune system from attacking its own fellow cells. These cells are useful in adaptive immunity as well as autoimmunity. B cells and their antibodies, both natural and adaptive, play a fundamental role in the immediate and future defense against microbes.

B cells types

  • Plasma B cells

Plasma B cells are produced when the B cells are exposed to a specific antigen. Plasma cells help to produce antibodies which assist in the destruction of microbes by binding to them. They differentiate from B cells upon stimulation by CD4+ lymphocytes. Plasma cells play a vital role in maintaining a healthy immune system by secreting large amount of antibodies.

  • Memory B cells

Memory B cells store the information of antibodies that are needed to tackle specific antigens. These cells then divide into plasma cells, which produces antibodies. These antibodies help in the destruction of microbes or antigens by binding to them. If the same antigen are detected in the body again, the memory cells are activated and they rapidly divide by mitosis.

  • B 1 cells

These cells are the subclass of B cells which are produced in the fetus. These cells show preferential responses to T cell-independent antigens and operate in the innate response to infection by viruses and bacteria. The B receptor cells of conventional B2 cells are more diverse than B1 cells. These cells express high levels of surface IgM (Immunoglobulin M), low levels of, low levels of IgD (Immunoglobulin D) and, express low level of CD5. There are increased numbers of B1 cells in people suffering from some autoimmune disorders. B1 cells can be further differentiated into B1 a cells and B1 b cells.

  • B cells lymphoma

B cells are vital immune system cells as they play a distinct role in defending the immune system. White blood cells are divided into T cells and B cells. These cells develop and mature in the lymph nodes. Lymphoma is a type of cancer that begins in the lymphocytes of the immune system forming a solid tumor of lymphoid cells. In lymphoma B cells tends to grow abnormally due to genetic disorder. These abnormal B cells become cancerous and subsequently clone themselves which causes the cancerous cells to proliferate. There are different types of lymphoma and they are categorized according to the appearance and condition of the cancerous B cells. As B cells develop and mature in lymph nodes, these nodes appear to be swollen since cancerous cells rapidly divide in these areas.

A look at some of the major types of B cell lymphomas:

  • Hodgkin’s Lymphoma

Earlier known as Hodgkin’s disease and named after Thomas Hodgkin who was the first to report the abnormalities in the lymph system, Hodgkin’s lymphoma is a type of cancer of the white blood cells called lymphocytes.  The disease spreads in an orderly manner from one lymph node group to another and displays systemic symptoms with advanced disease. Hodgkin’s lymphoma cells, when examined under a microscope, display multinucleated Reed-Sternberg cells (RS cells).

Generally Hodgkin’s Lymphoma occurs either in youngsters in the age groups of 15-35 or in people over the age of 55. It is one of the rare forms of cancer that is curable and the chances of survival are almost 90%, if the disease is detected in its early stages. Hodgkin’s Lymphoma is also one of the few forms of cancer that can be cured even in advanced stages.   Generally, the mode of treatments includes chemotherapy or radiation therapy.  Many patients who are successfully treated and enter remission generally go on to live long lives. Studies have shown that patients with a history of infectious mononucleosis due to Epstein-Barr virus may have an increased risk of HL.

  • Non Hodgkin’s Lymphoma

Non-Hodgkin lymphomas or NHLs are a group of blood cancers that include any kind of lymphoma except Hodgkin’s lymphomas.Non-Hodgkin lymphoma affects immune system cells called lymphocytes. Lymphocytes are part of the immune system that protects the body from infection and disease. This type of lymphoma generally develops in the lymph nodes and starts to proliferate in the blood, liver, spleen and bone marrow. It is more than five times as common as the other major type of lymphoma. Fatigue or weakness, high fever, chest pain, pain in the abdomen, heavy breathing, weight loss, and swollen lymph nodes in the neck, armpits and groin are some of the common symptoms associated with Non Hodgkin’s Lymphoma. There are about 35 different types of non-Hodgkin’s lymphoma and they are generally described by how quickly the cancer grows (low-grade, high-grade or aggressive).

  • Follicular Lymphoma

Follicular lymphoma is a cancer of B lymphocytes and it is generally classified as Non-Hodgkin’s lymphoma. This cancer starts to proliferate in the lymph nodes and then spreads into the blood and bone marrow. Liver and spleen are usually affected in more severe stages of follicular lymphoma.

Follicular lymphoma is the most common type of cancer which is not infectious and cannot be passed to other people. It develops slowly and often converts into diffuse large B cell lymphoma.

Lymph node swelling, fatigue, weight loss, fever, lump in neck, groin and armpit are some of the common symptoms that are associated with follicular lymphoma.

  • Burkitt’s Lymphoma

Burkitt’s lymphoma is a cancer of B cell lymphocyte and it usually affects children. The main cause of Burkitt’s lymphoma is linked to Epstein-Barr virus (EBV) and it is an uncommon type of Non Hodgkin lymphoma (NHL). This virus also causes infectious mononucleosis. When B cells become cancerous and start to proliferate, they form malignant tumors.

If Burkitt’s lymphoma is diagnosed at early stages, the prognosis for patients could prove to be quite effective. The African population is at a higher risk of developing Burkitt’s lymphoma.

Endemic and sporadic are two main forms of Burkitt’s lymphoma. In case of Endemic Burkitt’s lymphoma, tumor usually grows along the jaw bone and Sporadic Burkitt’s lymphoma mainly targets the intestine.

Fatigue or weakness, high fever, chest pain, pain in the abdomen, heavy breathing, weight loss, and swollen lymph nodes in the neck, armpits and groin are some of the common symptoms associated with Burkitt’s lymphoma.

  • Marginal Zone Lymphomas

Marginal Zone lymphoma is a Non Hodgkin’s Lymphoma which is a relatively uncommon type of B cell lymphoma. This lymphoma develops when damaged immune system cells changes the behavior of the cells, leading to the abnormal production of proteins and causes sustained rapid cell division.

This cancer starts to proliferate in the area known as marginal zone which is present in B cells. Marginal zone lymphoma can be categorized into Nodal marginal lymphoma, Extranodal marginal lymphoma of mucosa associated lymphoid tissue (MALT) and splenic marginal zone lymphoma.

Indigestion, weight loss, stomach bleeding and fatigue are some of the common symptoms of marginal zone lymphoma.

  • Mantle cell Lymphoma

Mantle Cell Lymphoma is an exceptional type of non-Hodgkin’s lymphoma which usually begins with lymph node area called as mantle zone enlargement and then spreads to other tissues such as the bone marrow, liver and gastrointestinal tract.

Men are at a higher risk of developing mantle cell lymphoma as compared to women. Mantle cell lymphoma is generally developed due to genetic disorder. This lymphoma is usually slow but can get aggressive over a period of time.

Patients suffering from mantle cell lymphoma may suffer from swollen glands, fever and night sweats. When the intestine is affected by this lymphoma, it can give rise to symptoms such as abdominal pain and diarrhea.

  • Large cell Lymphoma

Large cell lymphoma is the most common type of B cell lymphoma. This lymphoma is highly aggressive and generally affects the immune system cells of the body i.e. B cells and T cells. Large cell lymphoma affects adults as well as children.

Diffuse large cell, diffused mixed cell and Angioimmunoblastic lymphoma are some of the major types of large cell lymphoma. Diffuse Large B cell Lymphoma (DLCL) is a common Non Hodgkin’s lymphoma which targets B cells. This lymphoma is more common in men as compared to women.

This lymphoma causes painless swelling in the neck, armpit or groin due to enlarged lymph nodes. Unexplained weight loss, night sweats, fever and fatigues are the common symptoms associated with DLCL.

Diffused mixed cell lymphomas are the intermediate grade lymphomas of mixed cellular composition. Angioimmunoblastic lymphoma is an aggressive cancer which targets T cells of the immune system. The symptoms for Angioimmunoblastic lymphoma are similar to diffuse large B cell lymphoma.

B cells differentiation

B cells differentiation is a process by which B lymphocytes transform into plasma cells. B lymphocytes only express immunoglobin on its surface but do not produce antibodies. They produce antibodies only when B cell receptors (BCR) bind to a specific antigen. When BCR binds to an invading microbe, B cells multiply and differentiate into plasma cells which help to produce antibodies. When an antigen is T dependent, antibodies are produced with the help from T cells and the signal for activation comes from the BCR.

B cells Leukemia

B cells Leukemia also known as lymphoid leukemia is a blood cancer in which normal blood cells change and grow uncontrollably. The blood cells (Red blood cells, white blood cells and platelets) play an important role in carrying oxygen, fighting infections and help blood to clot.

This cancer affects the bone marrow, which helps to produce these vital immune cells. B cell leukemia develops when the white blood cells lose pieces of DNA and start to proliferate rapidly.

There are different types of lymphoid leukemia which affects B cells such as

  • acute lymphocytic leukemia
  • chronic lymphocytic anemia
  • acute myeloid leukemia
  • prolymphocytic leukemia
  • hairy cell leukemia (HCL)
  • chronic myeloid leukemia

Exposure to chemical carcinogens such as benzene is one of the major causes for lymphoid leukemia. Research has shown that extensive exposure to radiation can cause some types of leukemia, including acute and myeloid leukemia.

 

B cells and T cells

B cells and T cells are two types of white blood cells which help boost the immune system by fighting diseases or infections that are caused due to invading microbes, pathogens, viruses or bacteria. These cells are specific to a particular antigen and are able to bind to a particular molecular structure. They are primary membrane proteins and are present in thousands of identical copies that are exposed at the cells surface.

The white blood cells known as lymphocytes, that include T-cells and B-cells, destroy antigens directly. The lymphocytes act as the defending army of the human immune system providing a shield against several diseases and viruses. T dependent antigens help the B cells by producing antibodies. When T cells and B cells starts to proliferate abnormally, they tend to get cancerous.

Severe combined immunodeficiency (SCID) is a type of immune deficiency which is caused due to lack of B and T lymphocytes. Insufficient lymphocytes make it impossible for the immune system to fight against any infections. T cells are involved in killing viral infected cells, tumor cells and parasites whereas B cells produce antibodies to kill these viral infected cells.

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