Specific 1) a on disease organisms are mounted by the immune system. The immune response 2)i complex interactions between components of the lymphatic system and the blood. Any foreign particle may act as an 3) a____, that is, a substance that provokes a response by the immune system. This response comes from two types of lymphocytes that circulate in the blood and 4) l system. One type, the T cells (T lymphocytes), 5) m in the thymus gland. They are capable of attacking a foreign cell directly, producing 6) cell-m____ immunity. Macrophages, 7)d of monocytes, are important in the function of T cells. Macrophages take in and process foreign antigens. A T cell is 8) a____ when it contacts an antigen on the surface of a macrophage in combination with some of the body’s own proteins. The B cells (B lymphocytes) mature in 9) l____tissue. When they meet a foreign antigen, they multiply rapidly, transforming into10) p____cells. These cells produce antibodies, also called 11) i____ (Ig), that inactivate an antigen. Antibodies remain in the blood, often providing long-term immunity to the specific organism against which they were formed. Antibody-based immunity is referred to as humoral immunity.