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 body contains millions of different T-cells, each able to respond to one specific antigen. The T-cells secrete interleukin 2. Interleukin 2 causes the proliferation of certain cytotoxic T cells and B cells. From here, the immune response follows 2 paths: one path uses cytotoxic T cells and the other uses B cells. Cytotoxic T Cell Pathway The cytotoxic T cells are capable of recognizing antigens on the surface of infected body cells.