Agranulocytes are leucocytes with no visible granules in their cytoplasm and a nucleus that is not lobed. They make up about 30% of all leucocytes. There are two types: monocytes and lymphocytes.
Monocytes
• the largest leucocytes, up to about 20 µm across
• large kidney-shaped (bean-shaped) nucleus
• about 2 to 8% of leucocytes
• circulate in the blood for a day or two, then leave the capillaries and enter the tissues, where they develop into macrophages
• macrophages are long-lived phagocytes that engulf pathogens and debris. After digesting a pathogen they display its antigens on their surface, acting as antigen-presenting cells that activate lymphocytesLymphocytes
• small cells with a large, round nucleus that fills almost the whole cell, leaving only a thin rim of cytoplasm
• about 20 to 30% of leucocytes
• responsible for the specific immune response: each lymphocyte recognises one particular antigen
• B lymphocytes (B cells) develop into plasma cells that secrete antibodies; some become memory cells
• T lymphocytes (T cells) mature in the thymus; they include T helper cells, which coordinate the response, and T killer cells, which destroy infected body cells
• found in large numbers in the lymph nodes as well as in bloodOn a stained blood smear, a cell with a round nucleus that almost fills it is a lymphocyte, while a larger cell with a kidney-shaped nucleus and more cytoplasm is a monocyte.
Monocytes• the largest leucocytes, up to about 20 µm across
• large kidney-shaped (bean-shaped) nucleus
• about 2 to 8% of leucocytes
• circulate in the blood for a day or two, then leave the capillaries and enter the tissues, where they develop into macrophages
• macrophages are long-lived phagocytes that engulf pathogens and debris. After digesting a pathogen they display its antigens on their surface, acting as antigen-presenting cells that activate lymphocytesLymphocytes
• small cells with a large, round nucleus that fills almost the whole cell, leaving only a thin rim of cytoplasm
• about 20 to 30% of leucocytes
• responsible for the specific immune response: each lymphocyte recognises one particular antigen
• B lymphocytes (B cells) develop into plasma cells that secrete antibodies; some become memory cells
• T lymphocytes (T cells) mature in the thymus; they include T helper cells, which coordinate the response, and T killer cells, which destroy infected body cells
• found in large numbers in the lymph nodes as well as in bloodOn a stained blood smear, a cell with a round nucleus that almost fills it is a lymphocyte, while a larger cell with a kidney-shaped nucleus and more cytoplasm is a monocyte.