A lymphoproliferative disorder of granular lymphocytes with a novel phenotype and suppressor function

In this study we have identified and characterized an expanded granular lymphocyte population in a patient with anemia and granulocytopenia. Granular lymphocytes were identified through the presence of cytoplasmic azurophilic granules, the dispersed granular pattern of cytochemical staining for acid hydrolases, and the ultrastructural localization of acid phosphatase within the granules. The surface phenotype of the granular lymphocytes was E⁺, FcR^-, Leu 4⁺, Leu 2⁺, D 12⁺ (Leu 15⁺), OKM1⁺, and Leu 7⁺. This phenotype has not been reported previously in patients with similar features. Functional studies on FACS-purified populations showed that the patient's granular lymphocytes responded poorly to T-cell mitogens and were inefficient in NK and ADCC assays but exerted a potent suppressor effect on both T-cell proliferation and B-cell differentiation. The phenotype and functions of the expanded granular lymphocyte population correspond to those of a subset of normal E rosette-forming granular lymphocytes.