Final answer:
Lymphocytes are crucial white blood cells for the immune response, comprising about 20-30% of leukocytes with major types being B cells and T cells. They originate from lymphoid stem cells and mature in lymphatic tissues, with a lifespan ranging from weeks to years.
Step-by-step explanation:
Lymphocytes are a subtype of white blood cells vital for the immune response. They emerge from lymphoid stem cells in the bone marrow and develop further within the lymphatic system. Lymphocytes account for approximately 20-30% of all leukocytes (white blood cells) present in our blood circulation. Within the lymphocytes population, we have two major types: B cells and T cells. B cells are associated with the humoral immune response and mature in the bone marrow, whereas T cells are linked to the cell-mediated immune response and mature in the thymus.
While B cells compose about 10 to 20 percent, T cells represent approximately 80 to 90 percent of the lymphocytes in the circulating blood. The body houses as many as two trillion lymphocytes, which form about a quarter to a third of all white blood cells; however, fewer than half are found in the blood itself, with the rest primarily in the lymphatic tissues such as the lymph nodes, spleen, and other organs of the immune system. As for the longevity of these cells, the lifespan of lymphocytes can significantly vary, with some living for weeks while others can survive for years, contributing to the body's long-term immunity.