As they are generated continuously, millions of B cells are made in the human body each day, making them the most common type of lymphocyte. You might think B-cells got their name because they are made inside your bones. B cells are produced in the bone marrow, which provides a steady supply of them to the body. They are made in the bone marrow, but B cells mature in the spleen and T cells mature in the thymus. They later mature into one of two types of cells: plasma B cells and memory B cells. It is true that most blood cells are made inside the bone marrow, but that is not where the “B” in B-cells came from. The precursors of T cells are also produced in the bone marrow but leave the bone marrow and mature in the t hymus (which accounts for their designation). B-Cell. B lymphocytes (often simply called B cells) and T lymphocytes (likewise called T cells). B cells are produced in the b one marrow.