Severe aplastic anemia associated with chronic natural killer cell lymphocytosis

Chronic natural killer (NK) lymphocytosis involves a persistent increase in CD56(+) large granular lymphocytes (LGLs) that is sometimes associated wit h immune-mediated complications, such as anemia and neutropenia. However, a plastic anemia (AA) is a rare complication. Here we describe 2 patients wit h severe AA who presented with persistent increases in NK cells. Their LGLs were positive for CD56, CD16, and intracellular interferon (IFN)-gamma but negative for CD3, Fas-ligand, and T-cell receptor rearrangement, findings that are compatible with NK cells. Not only the number of NK cells, but NK activity as well, was increased in both patients. The number of NK cells ch anged according to hematologic recovery and relapse in 1 case. Thus, there seemed to be a close relationship between NK cells and the progression of A A, at least in this instance. Further investigation of the clinical course of similar cases and the characteristics of NK cells is necessary. Int J He matol. 2000,72:463-465. (C)2000 The Japanese Society of Hematology.