Sometimes a firm outer layer surrounds the mass of macrophages and lymphocytes, the caseous center enlarges, and an air filled tuberculosis cavity is formed where the bacilli can multiply extracellularly. At some point the tubercule ruptures and the bacteria enters the bronchioles and spreads throughout the respitatory system and two other systems. T cell Receptor Proteins T cells are the elements of the cell mediated immune response and are immunologically specific. T cells have specific receptors for antigens on their plasma membrane surface but they cannot bind to free antigens. The recognition sites of this T cell receptor extend out from the membrane and have a terminal variable section complementary to antigens.
T cells respond to antigens exposed on the surfaces of macrophages.
Only one gene of each pair on the MHC can code for the antigen for tuberculosis. Class II antigens are required for T cel communication with macrophages and B cells. Part of the T cell receptor must recognize a class II antigen on the adjacent cell before the T cell can secrete lymphokines, soluble mediator protein necessary for the immune response. Goals of Research for TB immune response In tuberculosis, when the tuberculosis bacterium is phagocytosed by a macrophage the bacterial antigens are moved to the surface of the macrophage where they are presented with class II MHC and recognized by the receptor protein on the surface of a T helper cell. The T helper cell secretes interleukin II which activates B cells and cytotoxic T cells.