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.
Some B cells change into memory cells, which remember that specific antigen, and others change into plasma cells. Helper T cells help B cells in this process. Plasma cells produce antibodies that are specific to the antigen that stimulated their production.After the first encounter with an antigen, production of enough of the specific antibody takes several days.Thus, the primary immune response is slow.ome helper T cells help B cells produce antibodies against foreign antigens. Others help activate killer T cells to kill infected or abnormal cells or help activate macrophages, enabling them to ingest infected or abnormal cells more efficiently.