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 adaptive immune response can be either humoral or cell-mediated. The humoral response is mediated by B lymphocytes, which release antibodies specific to the infectious agent. The cell-mediated response involves the binding of cytotoxic T lymphocytes to foreign or infected cells, followed by the lysis of these cells.he components of the innate immune system provide a first line of defense against infection. Physical barriers to infection include skin, which prevents pathogen penetration, and bodily fluids like mucus, which collect and clear pathogens.