• Hairy cell leukemia;
  • HLA-DR;


Spiro and coworkers found a 35 000 dalton membrane protein (p35) expressed abundantly in hairy cells of a subset of white, American patients with hairy cell leukemia. They subsequently identified p35 to be the human homologue of murine Ii, an electrophoretically invariant protein associated with Ia molecules. Using related analytical techniques, we have studied leukemic cells of two blood and one splenic samples from three Japanese patients with hairy cell leukemia and have demonstrated abundance of p35 in the splenic and one of the blood samples. The second blood sample was negative for p35 by our method of analysis, but the same hairy cells became positive for p35 at 2 months in culture and negative again at 4 months in culture. All 3 samples of this patient (fresh hairy cells and cultured cells at 2 and 4 months) remained consistently positive for Ia and for light chain-restricted immunoglobulin. Control cells from one each of acute lymphoblastic leukemia and Burkitt's lymphoma were negative for abundant p35 expression after culture as well as in the fresh state. One can conclude that the Japanese form of hairy cell leukemia, while varying in several distinct clinical and laboratory features from hairy cell leukemia in caucasions, is characterized also by abundant expression of p35 as seen in a subset of white patients. In addition, this expression of p35 is developed by hairy leukemic cells in culture initially but is lost upon longer term culture, in parallel with the level of tartrate-resistant acid phosphatase reactivity.