Morphology of Original and Transplanted Thymuses in Severe Combined Immunodeficiency

Abstract

Twenty-six patients with severe combined immunodeficiency (SCID) were examined. In 20 cases no defect of the biochemical pathways was found; 6 cases showed a deficiency in adenosine deaminase (ADA) activity. In 19 cases histological sections of the thymus were available. In 3 cases, in addition to the original thymuses, transplanted thymic allografts were microscopically examined. The thymus in SCID without abnormality of the ADA pathway showed a uniform dysplastic pattern with only moderate variations related to mode of inheritance and length of survival. The thymus in SCID with ADA deficiency displayed a heterogeneous pattern ranging from almost normal to a completely dysplastic structure, whereas the transplanted thymic allografts presented either a normal or a dysplastic appearance. The morphology of the thymus is not pathognomonic of any given biochemical defect, clinical course, or type of SCID. SCID with apparently normal biochemical pathways probably results from a variety of pathogenetic mechanisms.

Key Words:

• severe combined immunodeficiency
• thymus
• thymic morphology
• adenosine
• deaminase deficiency
• thymic allografts