Acid alpha-naphthyl acetate esterase in hairy cell leukemia cells and other cells of the hematopoietic system.

The activity of alpha-naphthyl acetate esterase at an acid pH (ANAE) was investigated in 10 cases of hairy cell leukemia. All 10 cases, including two cases with only a few tartrate-resistant acid phosphatase-reactive cells, revealed a moderate or strong ANAE reaction. There was a characteristic pattern of activity consisting of small, medium-size, or large distinct granules often distributed in a semicircle in the cytoplasm, but sparing the nucleus of hairy cells. This reaction pattern was not found in T cells, T cell-derived leukemias, normal B cells, a number of B-cell lymphomas, myeloid cells, myeloid leukemias (including monocyte-derived leukemias), reticulum cell sarcoma, or malignant reticulosis. The cells from some B-cell lymphomas and plasmacytoma showed a relatively homogeneous pattern of fine or moderately coarse ANAE-positive granules that was similar to that of hairy cells only in some cases of plasmacytoma. Thus, fine to coarse granular ANAE reactivity is characteristic of hairy cells and is of potential diagnostic value for hairy cell leukemia.