THE IMMUNOLOGICAL SIGNIFICANCE OF THE THYMUS

Abstract

Summary This is an account of the function of the thymus from the point of view of an immunologist ; it contains elements of speculation, but is based on a considerable and rapidly growing body of factual material. The postulated relation of the thymus to the initiation of autoimmune disease is the justification for bringing the subject before a predominantly clinical audience. The thymus is regarded as the chief “first level” immunological organ in which the lymphoid cells arise which proliferate to produce functionally active descendant or collateral cells in the “second level” immunological organs, spleen, lymph nodes, bone marrow and local lymphoid‐cell aggregations. The mutant cells which give rise to the forbidden clones of autoimmune disease must frequently have a thymic origin, which can be recognized by the occurrence in the thymic medulla of germinal centres and lymph follicles. If this hypothesis has a wider application than the two conditions specifically discussed in this paper, myasthenia gravis and a natural autoimmune disease of mice, there is a call for intensified search for possible thymic disorder in all human autoimmune conditions. Positive results might justify considering thymic irradiation or removal as therapeutic measures in selected cases.