Diagnostic dilemma of a 13-month-old boy with 'late-onset' combined immunodeficiency.

A 13-month-old boy had a "late-onset" form of combined immunodeficiency and a fulminant Pneumocystis carinii pneumonia of one month's duration. There was no evidence of cutaneous-delayed hypersensitivity responses to diphtheria-tetanus toxoids, Candida albicans, or streptokinase-streptodornase, or of lymphocyte DNA synthesis after in vitro stimulation with the mitogens phytohemagglutinin and concanavalin A, and only 2% to 4% of peripheral blood E-rosetted T lymphocytes. The serum IgM level was normal (62 mg/dL), whereas the other immunoglobulins were markedly reduced. Despite an increased number of Ig-bearing lymphocytes, in vitro Ig secretion after pokeweed mitogen stimulation was substantially reduced. The thymus gland was dysplastic with no Hassalls' corpuscles or thymocytes, and other lymphoid organs showed depletion of T-dependent areas to a greater extent than the B-dependent areas.