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.
T cell mediated B cell activation. IMMUNE SYNAPSE The activation of T lymphocytes is mediated by; the interaction of T cell antigen receptors (TCRs) with their ligands (major histocompatibility molecule-peptide complexes, MHC-peptide), and by a specific co-stimulatory signal like CD28 and B7 or CD40L and CD40.