Overview. Immune function is helped by two kinds of white blood cells. The âB cellsâ (so-called because they develop in bone marrow) produce antibodies. The âT cellsâ (so-called because they develop in a small organ called the thymus gland) are responsible for a variety of other immune responses. These responses include: 1  direct attacks on foreign substances such as bacteria, viruses, or foreign tissues; 2  augmenting the B cell response; and.