Omental milky spots are especially large and numerous in New Zealand Black (NZB) mice, which are known to develop spontaneous autoimmune diseases. We investigated omental milky spots in NZB mice by light and electron microscopy. The milky spots were composed of abundant lymphocytes/plasma cells with macrophages, neutrophils, eosinophils, megakaryocytes, and various stromal cells. In addition, clustered neutrophils in various maturation stages with occasional mitotic figures were frequently present in the milky spots: apparent neutrophilic myelopoiesis was present. The presence of megakaryocytes was sporadic. Considering the giant size of megakaryocytes, their direct migration into the milky spots from the bone marrow or spleen seems improbable. Thus, the presence of megakaryocytes was interpreted as probable megakaryopoiesis. Erythroblasts were not contained in the milky spots. These findings seem to indicate that the milky spots in NZB mice represent a special type of lymphoid tissue with active neutrophilic myelopoiesis and probable megakaryopoiesis. Reticulum cells in the milky spots in NZB mice had well-developed dense bodies consisting of clustered parallel tubules that showed a hexagonal array. However, the biological significance of these cells remains unknown.

A patient with M-proteinemia (IgM, kappa type), lymphocytosis, anemia, and massive splenomegaly, was diagnosed as having Waldenström's macroglobulinemia (WM). Since this case was refractory to chemotherapy, splenic irradiation was performed, which effectively reduced the serum IgM level, spleen size, and lymphocyte counts; however, its effect was transient. Splenectomy was then carried out. The spleen contained abundant IgM-producing lymphocytes, and after splenectomy, the serum IgM values decreased and the peripheral blood counts returned to near normal. The transient increases of serum IgM occurred during two infectious episodes postoperatively. The patient has now been in a satisfactory remission for six years after splenectomy. The removal of an IgM-producing/secreting site and release from hypersplenism may be the major mechanisms involved in achieving the durable remission after splenectomy. In individual cases of WM with massive splenomegaly, we recommend splenectomy as part of the management of this disorder.

The bone marrow of a 53-year-old woman with acute myeloid leukemia (AML) with disseminated intravascular coagulation was investigated by transmission electron microscopy. The patient had a preceding granulocytic sarcoma, and subclinical disseminated intravascular coagulation occurred concomitantly with the development of AML. Ultrastructural findings of the bone marrow at the onset of AML revealed the following: (1) The cytoplasm of the leukemic cells showed frequent fragmentation, resulting in the formation of abundant cytoplasmic fragments. (2) These cytoplasmic fragments were surrounded by abundant fibrin fibers, forming the fibrin-cytoplasmic fragment complex (FCF complex). (3) Slight fibrin deposition was seen around the leukemic cells and in the intercellular space of the bone marrow. Fibrin deposition in the bone marrow is thought to represent morphologic evidence of disseminated intravascular coagulation. The damage on the leukemic cell surface due to the cytoplasmic fragmentation seems to be closely related to the development of disseminated intravascular coagulation.

We used PUVA therapy in a patient with crisis-type adult T-cell leukaemia/lymphoma and generalized cutaneous leukaemic cell infiltration. PUVA proved very effective in reducing leukaemic cells and in clearing the eruption. To understand the way in which PUVA produced a reduction in the number of leukaemic cells, we examined peripheral blood cells by light and electron microscopy. Light microscopy was of little help, but electron microscopy revealed that PUVA induced apoptosis-like changes in circulating leukaemic cells. This suggests that apoptosis-like changes in leukaemic cells might be the reason for the success of this treatment.

Localization of IgG in bone marrow after high-dose intravenous immunoglobulin therapy (IVIG) was investigated via light and electron microscopy. IgG was incorporated into the cytoplasm of various types of bone marrow cells of all the three lineages, particularly in reticulum cells, fat cells, and megakaryocytes. In addition, both reticulum cells and fat cells showed many elongated cytoplasmic protrusions, which were in contact with the various types of blood cells, especially the megakaryocytes. A filamentous structure was also seen near the point of contact between the cells. Ultrastructural changes of macrophages in bone marrow after IVIG suggest that these cells were activated by IVIG.