While the tadpoles of competing species may complete metamorphosis in as little as just a few short months, Bullfrog tadpoles can remain in the same state for as long as one to two years before they actually become adult frogs.
Two types of white blood cells called lymphocytes are vital to the specific immune response. Lymphocytes are produced in the bone marrow, and mature into one of several subtypes. The two most common are T cells and B cells. An antigen is a foreign material that triggers a response from T and B cells.
Every effective immune response involves T-cell activation; however, T-cells are especially important in cell-mediated immunity, which is the defense against tumor cells and pathogenic organisms inside body cells.he immune system is a complex system of interacting cells whose primary purpose is to identify foreign (ânon-selfâ) substances referred to as antigens. The immune system provides protection from infectious disease by identify most of these microbes as foreign.