New Ideas on Amphibian Immunity: The Lymph Gland: A Generator of both T and B Cells

Abstract

Anuran amphibian larvae of the genus Rana possess three major lymphoid organs: the thymus, the lymph gland, and the spleen. Other accumulations of lymphocytes are present in the kidney, liver, and intestine. The thymus develops lymphocytes first followed by peripheral differentiation of other lymphoid centers. Since bone marrow is absent in larvae, there must be an alternative source of stem cells that differentiate into T cells under thymic influence or B cells under the influence of some other organ(s). We are concerned with the source of B cells after bullfrog larvae become immunologically mature. Such an organ should possess stem cells, and, to qualify further, it should play a major role in antibody synthesis. The lymph gland seems to fulfill this requirement. Contrary to our expectations, lymph glands can restore not only antibody synthesis but also transplantation immunity in a significant number of larvae. Thus, the lymph gland may house stem cells that can differentiate into B cells and T cells.