We used an Avidin-Biotin peroxidase complex (ABC) immunoperoxidase technique to evaluate the localization of IL-6 of human bone marrow cells in multiple myeloma (MM). The cellular distribution of IL-6 was determined at light and electron microscopic levels. The author's study indicated that cytoplasmic IL-6 was detected only in the myeloma cells of bone marrow cells. Immunoelectron microscopic (immuno-EM) study showed positive reactivity mainly in the perinuclear space (PNS), well-developed rough endoplasmic reticulum (RER), and Golgi area.

For simultaneous demonstration of cellular ultrastructure, myeloperoxidase activity, and presence of a membrane-bound antigen in a given blood cell, we examined three different fixatives: periodate-lysine-paraformaldehyde (PLP) and paraformaldehyde and glutaraldehyde for their applicability to preembedding electron microscopic immunocytochemistry using monoclonal antibodies and the avidin-biotin-peroxidase complex (ABC) technique. This procedure was examined in samples from 3 normal volunteers and 29 patients with acute lymphoblastic leukemia (ALL), chronic lymphocytic leukemia (CLL), lymphosarcoma cell leukemia (LSCL), blastic phase of chronic myelogenous leukemia (CML-BC), or other unclassified leukemias. PLP fixation preserved the immunoreactivity of surface glycoproteins as well as immunoglobulins to the most satisfactory extent. Leukemic cells fixed with PLP maintained their fine structural details, so that we could identify their cytoplasmic organelles, although glutaraldehyde produced the best preservation of cellular ultrastructure. In three patients with ALL, our method revealed that a significant portion of blasts possessed both lymphoid surface antigens and peroxidase-positive cytoplasmic granules. Our method was also useful in identifying the lineage of peroxidase-negative leukemic cells, including monoblastic leukemia and megakaryoblastic leukemia cells. Ultraimmunocytochemistry using PLP fixation and the ABC technique may be a promising strategy for determining the nature of blastic cells that remain unclear after a conventional work-up, for characterizing leukemic cells in patients with a relatively low blast cell count in the bone marrow or peripheral blood, and for estimating the presence and frequency of leukemia with multilineage expression.

We report ultrastructural evidence of the phagocytic potential of plasma cells and myeloma cells. The incubation of plasma cells and myeloma cells in vitro with horseradish peroxidase (HRP) and cationized ferritin (CF) allows the tracing of fluid-phase and receptor-mediated pathways. Surface-bound ligands (CF) and solutes (HRP) taken up in primary pinocytic vesicles are internalized to the endosomal compartment. After 1 hr of incubation, CF was found not only in plasma cells but also in myeloma cells. Reaction products of HRP were observed only in myeloma cells. In myeloma cells, however, HRP was located only in the lysosomal system, whereas CF was present within membrane cisternae as well as within lysosomes. These myeloma cells morphologically produced interleukin-6 (IL-6).