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 immune system can mount a variety of responses to attack specific invader organisms. One of these responses is coordinated by T-helper cells (also known as T cells, T4 cells, or CD4 cells), which act as a kind of orchestra conductor. The T-helper cells tell other cells what to do when this response is triggered.