Frequent Association of IgMλ with Crystalline Inclusions in Chronic Lymphatic Leukemic Lymphocytes

In four of 30 patients with chronic lymphocytic leukemia, studied by immunofluorescence, 1 to 31 per cent of peripheral blood lymphocytes were found to contain intracellular, rod-shaped inclusions that stained specifically for both μ and λ (IgMλ) determinants. Essentially all inclusion-containing lymphocytes exhibited monoclonal, membrane-bound IgMμ (M-IgM λ). However, only a minority of lymphocytes with M-IgM λcontained inclusions. On electron microscopy the homogeneous inclusions were found within the rough endoplasmic reticulum, and they exhibited an electrondense periodicity consistent with crystalline structure. In this series, the chance occurrence of crystals present solely in lymphocytes bearing M-IgMμ is 0.5 per cent. These studies indicate that in some patients with chronic lymphocytic leukemia, at least two morphologically distinct populations of neoplastic lymphocytes are present. (N Engl J Med 289:113–117, 1973)