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.
Antigens and the Immune System. When antigens enter the body, the immune system alarm is triggered. The first line of defense is for the B-lymphocytes, or B cells, to be sent out. These are special leukocytes, also called white blood cells. Their job is to tag the antigen so that the correct response can be made.