M-component-related diseases. In B-cell neoplasias (MM indicates multiple myeloma; WM, Waldenström macroglobulinemia; NHL, non-Hodgkin lymphoma; and CLL, chronic lymphocytic leukemia) the clinical pattern is usually dominated by systemic effects caused by expansion of the malignant clone, whereas the monoclonal protein may cause hyperviscosity syndrome or kidney damage. In less common disorders, the biologic effects of the monoclonal protein may account for most of the clinical manifestations and determine the prognosis. There are overlaps between these 2 groups; for instance, the IgM of a patient with Waldenström macroglobulinemia may have a cold agglutinin activity and a myeloma clone can secrete an amyloidogenic light chain. The left micrograph depicts myeloma bone marrow plasma cells stained with May-Grünwald-Giemsa; objective magnification, 100× (numeric aperture [NA] 1.30). The right micrograph depicts AL amyloidosis bone marrow plasma cells observed in immunofluorescence, using TRITC-conjugated anti-human lambda light chain antiserum from rabbit (Dako, Glostrup, Denmark), under a Nikon Eclipse E600 microscope (Nikon, Tokyo, Japan) equipped with a Nikon Pan Fluor 40×/0.75 NA objective. Image was photographed using a Leica DFC 480 camera (Leica Microsystems, Wetzlar, Germany), and was acquired using Leica IM50 Image Manager software. Illustration by Marie Dauenheimer.