The immunophenotype of hairy cell leukemia (HCL). Proposal for a scoring system to distinguish HCL from B-cell disorders with hairy or villous lymphocytes.

We have analysed the immunological profile of cells from 194 patients with a B-cell disorder associated with circulating hairy or villous lymphocytes. These included: 69 typical HCL, 25 HCL-variant and 100 splenic lymphoma with villous lymphocytes (SLVL). All cases were HLA-DR+, CD19+, CD2- and most expressed Smlg with light chain restriction. The kappa/lambda ratios were: HCL, 1.2; SLVL, 1.5; and HCL-variant, 0.55. The majority were FMC7+ (89-96% of cases) and membrane CD22+ (73-98% of cases) and often negative with CD5 and CD23, markers characteristic of chronic lymphocytic leukemia. CD24 was variably expressed ranging from 21% of cases in HCL-variant to 60% in HCL and 89% in SLVL; CD10 and CD38 were positive in one third of SLVL but usually negative in HCL and HCL-variant. Of the four markers considered typical of HCL, CD11c, CD25, HC2 and B-ly-7, CD25 and HC2 were consistently negative in HCL-variant and a minority of SLVL cases expressed CD25 or HC2+ or B-ly-7+; CD11c was positive in all three disorders (47 to 97% of cases). Based on the most common phenotype of typical HCL: CD11c+, CD25+, HC2+ and B-ly-7+, we propose a scoring system which considers the reactivity with each of these four markers and gives 1 point if positive and 0 points if negative. Scores range from 4 (typical of HCL) to 0 (atypical of HCL). 98% of HCL had high scores (3 or 4) whereas 88% of HCL-variant and 77% of SLVL scored 1 or 2 and no single case scored 3 or 4.(ABSTRACT TRUNCATED AT 250 WORDS)