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Because T and B Cells are the only cells in the organism capable of recognizing and responding individually to each antigenic epitope, T and B lymphocytes (T and B Cells) are engaged in the acquired or antigen-specific immune response. B cells can change into plasmocytes and are responsible for the production of antibodies (Abs). As a result, humoral immunity is dependent on B cells, whereas cell immunity is dependent on T cells. The ontogeny processes for each kind of lymphocyte are covered in this chapter, along with their basic characteristics, the many subpopulations described to date, the signaling pathways used to activate them, and their main functions based on the immunological profile they exhibit.
| Table of Content |
Key Terms: T lymphocyte, B cells, Antigens, Immunity, Lymphocytes, WBC, RBC, Nucleus, Immunoglobulin, Bone Marrow, Plasmocytes, antibodies, cell immunity
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T Cells
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An essential part of the immune system is the T lymphocyte (white blood cell). T cells are one of two types of lymphocytes that define the specificity of the immune response to antigens (foreign substances) in the body. B cells are the other type.
T cells mature in the thymus after originating in the bone marrow. T cells grow and differentiate into helper, regulatory, or cytotoxic T cells, as well as memory T cells, in the thymus. They are subsequently transported to peripheral tissues or circulated in the bloodstream or lymphatic system. Helper T cells secrete chemical messengers called cytokines after being triggered by the right antigen, which stimulates the development of B cells into plasma cells (antibody-producing cells). Regulatory T cells regulate immunological responses, as their name implies. Cytotoxic T cells connect to and kill infected and cancer cells after being stimulated by different cytokines.
Activation of T & B cell
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B Cells
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B cells are lymphocytes that are responsible for the humoral immunity component of the adaptive immune system. Antibodies are produced by these white blood cells, and they play an important role in immunity. A single circular nucleus can be found in each B cell.
Lymphocytes make up around 25% of all white blood cells, and B cells make up about 10% of all lymphocytes. The immune system creates antibodies, or Y-shaped chromosomes, in B cells to prevent foreign chemicals from hurting the body. On the surface of B cells are B cell receptors (BCRs), which they employ to bind to a specific protein.
When B cells bind to this protein, known as an antigen, antibodies are released, which adhere to the antigen and keep it from hurting the body. The B cells then produce cytokines, which attract other immune cells. They also give antigens to T cells, which identify them thanks to their T cell receptors (TCRs). The antigens are destroyed by the T lymphocytes.
B Cells
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Similarities Between B cells and T cells
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- B and T cells both originate from the bone marrow.
- These cells are involved in adaptive immunity.
- They are the lymphocytes.
- The cells are motile and nucleated.
- Both help in the protection of the immune system and the fight against infections.
- Both cells belong to the lymphatic system and are non-phagocytic.
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Properties of B cells and T cells
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These characteristics are shared by both B and T cells-
- They are membrane proteins that play an important role.
- They exist in a large number of identical copies that are visible on the cell surface.
- They are ready long before the cell even comes into contact with an antigen.
- They are encoded by genes, which are made up of a variety of DNA segments.
- They have a unique binding location.
- This site binds to an antigenic determinant or epitope, which is a part of the antigen.
- The binding, like that between an enzyme and its substrate, is based on the complementarity of the receptor's surface and hence the epitope's surface.
- Non-covalent forces bond the molecules together (again, like an enzyme binding to its substrate).
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Differences between B Cells and T Cells
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The detailed difference between B cells and T cells are mentioned below in the table.
| Properties | B-Cells | T-Cells |
|---|---|---|
| Name | B lymphocytes | T lymphocytes |
| Origin | Bone Marrow | Thymus |
| Position | Outside Lymph Node | Interior of Lymph Node |
| Membrane receptor | BCR (= immunoglobulin) for antigen | TCR for antigen |
| Connections | B-cells can attach directly to antigens on the surface of an invading virus or bacteria. | T-cells can only interact with virus antigens outside infected cells. |
| Tissue Distribution | Germinal centers of lymph nodes, spleen, gut, respiratory tract; also subcapsular and medullary cords of lymph nodes | Parafollicular areas of cortex in nodes, periarteriolar in spleen |
| Life Span | Life span is short | Life span is long |
| Surface Antibodies | Surface Antibodies present | Absence of surface antibodies |
| Secretion | They secrete antibodies | They secrete Lymphokines |
| Function | B-cells form humoral or antibody-mediated immune systems (AMI). | T-cells from a cell-mediated immune system (CMI). |
| Blood | 20% of lymphocytes | 80% of lymphocytes; CD4 > CD8 |
| Formation | They form plasma cells and memory cells. | They form killer, helper, and suppressor cells. |
| The movement to Infection Site | Plasma cells do not migrate to the site of infection. | Lymphocytes migrate to infection sites. |
| Function | Plasma cells do not react against transplants and cancer cells. | Killer cells react against transplants and cancer cells. |
| Function | Plasma cells have no inhibitory effect on the immune system. | Suppressor cells inhibit the immune system. |
| Function | They defend against viruses and bacteria that enter the blood and lymph. | Defend against pathogens including protists and fungi. |
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Things to Remember
- T cells mature in the thymus after originating in the bone marrow.
- There are two main types of B cells. Plasma cells and Memory B cells.
- Helper T cells create a specialized immune response by activating other immune system cells.
- Plasma cells make a lot of antibodies, which stick to foreign invaders in your body.
- Memory B cells help your body in remembering foreign invaders if they infect you again.
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Sample Questions
Ques. How do the T cells activate? (2 Marks)
Ans. When MHC class II molecules, which are found on the surface of antigen-presenting cells, transmit peptide antigens to helper T cells, they become activated (APCs). They divide quickly after activation and secrete cytokines that regulate or assist the immune response.
Ques. How are B and T cells activated? (2 Marks)
Ans. T and B lymphocytes are activated when they detect tiny components of antigens, called epitopes, presented by APCs. An antigen is a macromolecule that interacts with immune system components. A single antigen may have numerous patterns that immune cells identify.
Ques. How long does it take for T cells to activate? (2 Marks)
Ans. It takes 7 to 10 days for many initial virus infections to activate and grow adaptive T cell immune responses, which corresponds to the time it takes for COVID-19 patients to recover or develop severe disease.
Ques. Can you boost your T cells? (2 Marks)
Ans. Vitamin D activates the immune system by priming the t-cells for action, allowing antibodies to combat infections more effectively. Vitamin D can be obtained from a variety of sources, including certain foods found in modern diets, but getting some sun is a fun way to get the vitamin.
Ques. Is T cell the same as CD4? (2 Marks)
Ans. CD4 cells, commonly known as T cells, are white blood cells that help your immune system fight infection. A CD4 count is used to monitor the health of the immune system in persons afflicted with HIV (human immunodeficiency virus) (human immunodeficiency virus). CD4 cells are attacked and destroyed by HIV.
Ques. How are B cells activated a level? (2 Marks)
Ans. When T helper cells produce substances, B cells become activated. When the antibody molecules on their cell surface attach to a complementary antigen, they become activated. Only the B cells with the correct-shaped antibodies will be triggered since various B cells have varied-shaped antibodies on their surface.
Ques. How do B cells turn into plasma cells? (2 Marks)
Ans. B cells differentiate into plasma cells, which produce antibody molecules that are very similar to the precursor B cell's receptors. These antibody molecules bind to the target antigen (foreign substance) and begin neutralization or destruction once released into the blood and lymph.
Ques. Where do B cells circulate? (2 Marks)
Ans. B cells that have not been activated circulate through the lymph nodes and spleen. They're mostly found in follicles and the peripheral zones around them. At extrafollicular regions where T cells are present in conjunction with antigen-presenting dendritic cells, circulating B cells may interact and be activated by T cells.
Ques. What is the first step in B cell activation? (2 Marks)
Ans. The functionality of antigen-binding receptors is assessed as the initial step in B cell maturation. Positive selection for B cells with normal functioning receptors is used to achieve this. Then, to decrease self-reacting B cells and reduce the likelihood of autoimmunity, a negative selection process is applied.
Ques. What happens if you don't have B cells? (2 Marks)
Ans. Your body would be less successful at fighting off a variety of common bacteria and viruses if you didn't have B-cells, and you wouldn't have the long-lasting "memory antibody" function that occurs after an infection or after being immunized against a specific infectious invasion.
Ques. How do B cells respond to antigens? (2 Marks)
Ans. On the surface of B cells are B cell receptors (BCRs), which they employ to bind to a specific protein. When B cells bind to this protein, known as an antigen, antibodies are released, which adhere to the antigen and keep it from hurting the body. The B cells then produce cytokines, which attract other immune cells.
Ques. What is the difference between B-cell and plasma cell? (2 Marks)
Ans. The main distinction between B cells and plasma cells is that B cells are white blood cells that manufacture antibodies against various pathogens as part of adaptive immunity, whereas plasma cells are activated B cells. B cells that have not been exposed to antigens are known as naive B cells.
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