- Lymphocytes are a type of white blood cell that play a central role in the body’s immune system, particularly in the adaptive immune response.
- They are primarily responsible for recognizing and responding to foreign invaders, such as bacteria, viruses, and abnormal cells like cancer cells.
- In healthy adults, lymphocytes account for about 20% to 40% of the total white blood cell count.
- These cells are found throughout the blood, lymphatic system, and various lymphoid organs such as the spleen and lymph nodes, where they coordinate immune responses.
- Lymphocytes typically appear as small, round cells with a large, dark-staining nucleus and a thin rim of cytoplasm when viewed under a microscope. Their size ranges from about 6 to 9 micrometers in their resting state, although they can become larger when activated during an immune response.
- Lymphocyte levels in the blood can increase in response to infections, particularly viral infections, or decrease in conditions that suppress the immune system.
- There are three main types of lymphocytes: B cells, T cells, and natural killer (NK) cells.
- B cells are responsible for humoral immunity, producing antibodies that target specific pathogens circulating in body fluids. When a B cell encounters a specific antigen, it can differentiate into a plasma cell that produces large quantities of antibodies specific to that antigen.
- T cells are central to cell-mediated immunity and come in different forms. Cytotoxic T cells directly attack and destroy infected or cancerous cells. Helper T cells assist other immune cells by secreting cytokines, which are signaling molecules that enhance the immune response. Regulatory T cells help maintain immune system balance by suppressing excessive immune responses, thereby preventing autoimmune diseases.
- Natural killer (NK) cells provide rapid response as part of the innate immune system. Unlike B and T cells, NK cells do not require prior exposure to a specific pathogen to recognize and attack infected or abnormal cells. They can quickly identify and kill virus-infected cells and tumor cells through the release of cytotoxic granules.
- Through these specialized cells, lymphocytes provide the body with the ability to recognize, target, and remember specific pathogens, ensuring a robust and coordinated defense against infections.
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