Combined immunodeficiency and thymic abnormalities.

Abstract

Severe combined immunodeficiency (SCID), although a relatively rare congenital disorder, is an important disease because it has taught us much about the function and interactions of T and B lymphocytes. It is also the only disease where consistently encouraging results have been obtained with bone marrow transplantation. Furthermore, it was the first immunodeficiency disorder to be identified with an enzyme deficiency and is the first disease to be successfully treated by enzyme replacement therapy. Isolated T cell defects may appropriately be discussed together with SCID, particularly since it is now apparent that some SCID patients have a predominantly T cell defect. Now that in-vitro tests are available to analyse both T and B cell functions separately in these patients the classification is likely to change and become more precise in the next few years. A major advance in understanding the differences between T and B cells at a biochemical level has come from the finding of a purine enzyme deficiency which causes a predominantly T cell defect. This should ultimately lead to the production of drugs which will selectively affect T or B lymphocytes.