The Role of the Thymus in Immune Responses – April 30, 1978

The Role of the Thymus in Immune Responses – April 30, 1978

The role of the thymus has only recently attracted attention; it was originally an important organ involved in immune responses. The thymus itself contains latent immune-active cells. It can also receive immune-active T cells from red bone marrow stem cells. Under certain conditions, these cells leave the thymus in the form of small lymphocytes and enter surrounding lymphoid tissues, becoming immune-active cells. Only in these peripheral lymphoid tissues—including lymph nodes and the spleen—can the cells truly become immune-active; if they remain in other tissues, not only do they fail to develop into active immune cells, but most of them die. Therefore, these peripheral lymphoid tissues outside the thymus are called thymus-dependent areas. There is also a theory that the thymus is an endocrine organ, capable of secreting one or more hormone-like substances that can stimulate the development of lymphoid precursor cells without immune activity in the surrounding lymphoid tissues into immune-active cells.