The thymus in rheumatic heart disease.

Thymic biopsy specimens obtained during thoracic surgery from 113 patients suffering from rheumatic heart disease, congenital heart disease and certain other miscellaneous diseases were studied at the light microscope level. Thymuses from patients with rheumatic heart disease showed certain changes consistent with the effects of a chronic inflammatory process, and which included in 37% of the cases, formation lymph follicles with germinal centres. The thymuses of adults with congenital heart disease showed a much lower incidence (10%) of such follicles as compared with those of children in this group, 25% of which showed this change. However, there was a relative absence of other thymic abnormalities in both children and adults with congenital heart disease. Patients suffering from a variety of other diseases, several of which are accepted as being of an autoimmune nature and in which thymic pathology is already well documented, also showed a high incidence (47%) of germinal centre formation within the thymus, and in certain instances other thymic changes. Lymph follicles with germinal centres presumably reflect a response to antigen, and it is suggested that these structures may occasionally arise in the thymus of normal individuals, particularly children and adolescents. However, in rheumatic heart disease, the formation of increased numbers of these structures within the thymus occurring in association with the other changes described, are interpreted as reflecting a chronic inflammatory process or `thymitis'. The possibility is discussed that this might represent an autoimmune reaction against a thymic component, and that this reaction could be triggered off by a common antigenic determinant shared with a streptococcus.