Final answer:
Lymphocytes are critical white blood cells within the immune system and make up about 20-30% of all leukocytes. They have a large nucleus and a small amount of cytoplasm, are located in blood and lymphatic tissues, and are key to adaptive immunity. The two primary types are B cells and T cells, with plasma cells and Natural Killer cells also being significant.
Step-by-step explanation:
Lymphocytes: Key Players in the Immune System
Lymphocytes are a type of white blood cell that play a critical role in the immune response. They are characterized by a large central nucleus surrounded by a thin layer of cytoplasm and are the only formed element of blood arising from lymphoid stem cells. Morphologically, B cells and T cells, the two basic types of lymphocytes, are identical, and they can be distinguished by their surface protein markers and the molecules they secrete.
Lymphocytes are quite prevalent, accounting for about 20-30 percent of all leukocytes. In terms of appearance, the nucleus is large relative to the cytoplasm, especially in smaller lymphocytes, giving the appearance of a 'halo' around the nucleus, and they typically stain dark with hematoxylin and eosin stains used in microscopy.
These cells are usually located throughout the body; they circulate in the bloodstream and lymph and reside in secondary lymphoid organs such as the spleen and lymph nodes.
Lymphocytes are crucial to the adaptive immune system, and there are two major types:
- B cells, which mature in the red bone marrow and are responsible for producing antibodies.
- T cells, which mature in the thymus and are involved in cell-mediated responses.
Additionally, plasma cells, which are differentiated B cells that secrete antibodies, and Natural Killer (NK) cells, which also play roles in the immune response, are considered types of lymphocytes.