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.
Introduction of T helper (Th) cell types and their functions. 1  In response to an infection, a variety of cells of the innate and adaptive immune systems become activated and collaborate in the effort to control and eliminate invading pathogens. CD4 T cells (also known as Th cells) play critical roles during adaptive immune responses .