Membrane phenotype and functional behaviour of T lymphocytes in hairy cell leukemia (HCL).

Abstract

D ESPITE some controversy, hairy cell leukemia (HCL) is generally considered to be a chronic B cell lymphoproliferative disorder of the adult age,‘~d although some very rare cases with T cell features have also been described.5.6 Throughout the course of this disease, the major jeopardizing factor is the high risk of infective episodes,‘.* particularly after splenectomy, that nonetheless still remains the primary and most beneficial type of therapeutic intervention.‘.” Several other hypothesis have been put forward to account for the high incidence of these infections, including neutropenia and monocytopenia. Interestingly however, patients with HCL generally have normal levels of serum immunoglobulins”,‘2 unlike in other chronic B cell leukemias, namely chronic lymphocytic leukemia (B-CLL). ‘The recognition of the close interaction between T and B lymphocytes and in particular of the regulating function of T cell subsets in the maturation and differentiation of B cells into antibody-producing plasma cells” has shed further light on the possible role played by T cell defects in the B cell disorders. Among the different B cell chronic leukemias, B-CLL has been the most thoroughly studied, and both the phenotypic and functional abnormalities of the T cell population have been described. Indeed, an imbalance in the distribution of T lymphocyte subsets with an increase in the proportion of T cells expressing a suppressorcytotoxic phenotype (Ty, OKTS positive cells) together with a decrease in the proportion of the T cells with a helper-inducer phenotype (Tp, OKT4 positive cells) has been demonstrated,‘J-‘X particularly in patients with more advanced disease.” In addition, several T cells functional defects, like a decreased response to mitogens,20 a reduced T colony forming capacity,2’.22 a diminished helper activity in a pokeweed mitogen (PWM)-stimulated system,23.24 and a depressed natural killer (NK) activity25.2h have also been extensively documented. These observations strongly suggest that T cell abnormalities may be implicated in the clinical and laboratory features