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Lymphocytes are a sort of white blood cell that comes in a variety of shapes and sizes. Each type of white blood cell has a specific function and they all unite to fight against disease and illness. Our immune system relies on white blood cells. They assist our body in fighting antigens such as bacteria, viruses, and other toxins that cause illness. If our immune system is weak, it means we don't have enough white blood cells in the bloodstream. Lymphocytes are a form of agranulocyte. B and T lymphocytes make up about 20-25 percent of white blood cells.
Read More: Immunity
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Key Words: Lymphocytes, Spleen, Tonsil, Lymph Node, Antigen, Pathogens, White blood cell, and Red Blood Cell.
Lymphocyte
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Lymphocytes make up about 99 percent of all lymphocytes. Immune cells that are stored in lymphoid organs such as the spleen, lymph nodes, tonsils, and other lymphoid organs are known as lymphocytes. They initiate the immunological response to a foreign infection.
- Lymphocytes are a type of white blood cell (leukocyte) that impacts the specificity of the immune response to pathogenic bacteria and other foreign substances.
- They play an important function in the immune system. Lymphocytes make up around 20 to 40% of the total amount of white blood cells in adults.
- They're found in the bloodstream and concentrate in central lymphoid organs and tissues including the spleen, tonsils, and lymph nodes, where the initial immune response is most likely to occur.
Read More: Blood
Types of Lymphocytes
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T cells, B cells, and natural killer (NK) cells are the three main types of lymphocytes. The big nucleus of lymphocytes is commonly used to identify them. By increasing our immune system, these cells protect our body from infections.
- B Cells
- T Cells
- Natural Killer (NK) Cells
Classification of Blood Cells
B Lymphocytes
B cells are named after the bursa of Fabricius, which is where they mature in birds and where they were first found. In humans and certain other species, the bone marrow is the primary site of B lymphocyte formation.
- The particular antibodies generated in response to the antigen are synthesized and expressed by the mature B cell.
- The membrane-bound immunoglobulin or antibody, also known as BCR or B-cell receptor, binds to the specific antigen.
- B cells that have been activated can then develop into plasma cells or effector cells.
- To fight the virus, they shed the surface antibody and begin making vast amounts of specialized antibodies.
- B cells are known to induce the humoral immune response because they create antibodies.
- After a first infection, memory B cells develop and persist in the blood for decades. They circulate in the bloodstream, identifying and acting on antigens that have already been infected.
- At birth, the B-lymphocyte system is fully established. Human B lymphocytes have an unknown origin, however in fetal B lymphocytes can be found in the yolk sac, omentum, and fetal liver. B-lymphocyte development takes occurs in the bone marrow after birth.
Read More: Types of White Blood Cells
T Lymphocytes
T lymphocyte is a type of leukocyte (white blood cell) that plays an important role in the immune system. T cells develop in the thymus after starting 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.
Natural Killer Cells
The innate immune system includes NK cells, which play a key role in protecting the host from malignancies and virally infected cells. These cells, which include macrophages and T lymphocytes, can also review the tasks of other cells. These killer cells are triggered to fight contaminated cells, and they belong to the cytokine and interferon families. Killer cells that have been activated release cytotoxic granules that aid in the destruction of transformed cells.
Read More: Difference between Monocytes and Lymphocytes
Lymphocytes Function
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Lymphocytes are important players in adaptive immunity. T cells are essential for cell-mediated immunity, while B cells are responsible for humoral immunity. B cells secrete antibodies that are carried via the bloodstream, allowing them to work across great distances, whereas T cells can move to target regions and act locally.
The acquired immune response is pathogen-specific. Once acquired, it is kept in the memory cell, triggering a substantially magnified secondary reaction when the infection is repeated.
Lymphocyte counts
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The typical lymphocyte count ranges from 1000 to 4800 cells per µl. The lymphocyte count has clinical importance whether it rises or falls. Lymphocytic lymphocytosis is a condition in which the number of lymphocytes in the body increases. It's a sign of viral infection, but it could also be caused by leukemia. Lymphocytopenia is a condition in which the lymphocyte count falls below the normal range. It's linked to immune deficiency diseases, starvation, and some hereditary conditions, among other things.
Read More: Pathogens: An Overview and Types of Pathogens
Structure of Lymphocytes
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Transmission microscopy revealed that the blood lymphocyte is spherical with a diameter of around 5 m. The nucleus contains an abundance of heterochromatin, a compacted electron-dense structure found in nonproliferating cells. The nuclei range in size from 0.5 to 1.4 m in diameter. The granular zone, which contains internuclear chromatin, is made up of three different and concentrically ordered structural units: the central region, or agranular zone; the center, fibrillar region; and, thus, the granular zone.
Things to Remember
- Interferons, a type of cytokine, also stimulate NK cells. Natural killer cells that have been activated release cytotoxic granules that kill infected cells.
- T helper cells have CD4 membrane glycoprotein on their surface and use class II MHC to recognize antigens.
- T cytotoxic cells have CD8 membrane glycoprotein on their surface and use class I MHC to recognize antigens.
- Memory T cells are antigen-specific T cells that live for a longer period.
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Sample Questions
Ques. What is the Function of Lymphocytes? (3 Marks)
Ans. The lymphocytes are part of our immune system, and the B cells assist in the production of antibodies that target and eliminate viruses and bacteria. T cells aid in the production of cytokines, which aid in the battle against foreign invaders. Lymphocytes in the blood have one basic function: to circulate throughout the body in search of infections that can harm the immune system.
Ques. How long do Lymphocytes live? What is the Role of Lymphocytes in Immune Response? (2 Marks)
Ans. Lymphocytes can live for days, weeks, or even years. Lymphocytes are a type of white blood cell that plays a vital part in the immune system since these cells determine whether an immune response is required when microbes or foreign substances are present.
Ques. What does a lymphocyte respond to? (3 Marks)
Ans. T- and B-cell development and activation. Yellow boxes indicate the central lymphoid organs, where lymphocytes originate from progenitor cells. Lymphocytes react to antigens in lymph nodes and the spleen, which are located in the peripheral lymphoid organs. Lymphocyte activation occurs when antigen-specific receptors on the cell surface of lymphocytes (B cells or T cells) are stimulated. The cells proliferate and develop into specialized effector lymphocytes as a result of this.
Ques. How long do lymphocyte cells live? (3 Marks)
Ans. The majority of lymphocytes have a limited life period, ranging from a week to a few months, but a small percentage live for years, creating a pool of long-lived T and B cells. Immunologic "memory," or a faster, more powerful reaction to a second contact with the same antigen, is accounted for by these cells.
Ques. What happens when a lymphocyte is activated? (3 Marks)
Ans. Lymphocyte activation occurs when antigen-specific receptors on the cell surface of lymphocytes (B cells or T cells) are stimulated. The cells proliferate and develop into specialized effector lymphocytes as a result of this. Plasma cells are effector B cells that release antibodies, while cytotoxic T cells and helper T cells are activated T cells.
Ques. Where are lymphocytes stored? (3 Marks)
Ans. Small, bean-shaped clumps of lymphatic tissue that line lymph veins are known as lymph nodes. They filter lymph and store lymphocytes, as well as debris, germs, and damaged cells (including cancer cells). The lymphocytes in the lymph nodes also fight germs and viruses found in the lymph.
Ques. How are lymphocytes transported? (3 Marks)
Ans. The lymphocytes are conveyed through lymph fluid and leave the node via efferent vessels to execute adaptive immune response functions in other areas of the body. Lymphatic vessels are a network of capillaries (microvessels) and a huge network of tubes that move lymph away from tissues throughout your body. As lymph moves into larger vessels called collecting ducts, lymphatic vessels collect and filter it (at the nodes).
Ques. Do helper T cells produce antibodies? (3 Marks)
Ans. Because they are necessary for practically all adaptive immune responses, helper T cells are arguably the most critical cells in adaptive immunity. They not only aid B cells in secreting antibodies and macrophages in destroying ingested bacteria, but they also aid cytotoxic T cells in killing infected target cells.
Ques. Write a brief note on the Structure of Lymphocytes. (2 Marks)
Ans. Nuclear pores and a perinuclear gap make up the nuclear membrane. Some lymphocytes can live for a week, while others might live for years. This is the average lymphocyte lifespan.
Ques. How the name natural killer cells coined? (2 Marks)
Ans. The cells are called "natural killer cells" since they don't need to be activated before killing cells that lack MHC (Major histocompatibility class) class I.
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