Final answer:
T cells mature in the thymus after originating as immature lymphocytes in the bone marrow. They travel to the thymus for maturation which is critical for developing a proper immune response that avoids attacking the body's cells.
Step-by-step explanation:
T cells develop in the thymus gland. They are a critical part of the adaptive immune response. These cells originate as immature lymphocytes in the bone marrow and travel through the bloodstream to the thymus, where they undergo a maturation process. In the thymus, immature T cells that express T-cell receptors (TCRs) complementary to self-antigens are eliminated to avoid autoimmune responses. Once mature, T cells circulate in the bloodstream and lymph fluid and settle in secondary lymphoid organs like the spleen and lymph nodes where they fulfill their role in immune defense.