Severe combined immunodeficiency with thymic mast cell hyperplasia.

The autopsy finding on an infant with severe combined immunodeficiency was marked thymic mast cell hyperplasia. The clinical immune status showed a deficit in T (thymus derived) lymphocytes and low immunoglobulin levels. The autopsy showed the histologic pattern designated thymic alymphoplasia and a marked lack of development of the reticuloendothelial organs. The mast cell hyperplasia may be the result of an antigenic stimulus early in embryonic life and/or the result of mast cell differentiation at the expense of normal thymic lymphoid development caused by a genetic defect.