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.
The many resulting T cells can then stimulate other T cells to attack the foreign pathogen, or they can stimulate B cells to produce antibodies. These antibodies, along with other cells in the immune system, then destroy the foreign invaders, helping to ensure the health of the individual.he macrophage is just one cell type that may present antigens in the MHCII complex; other cells, including B cells and dendritic cells, may also act as antigen-presenting cells (APC). Only a few helper T cells in the immune system will recognize the specific antigen presented by the APC.