Abstract
A diagnosis of plasma cell myeloma was made in a 6-year-old Holstein cow that showed continuous nosebleed, progressing emaciation, and hyperglobulinemia. Necropsy revealed enlargement of the caudal mesenteric lymph nodes. Lymph nodes and spleen were infiltrated by neoplastic plasma cells. Renal lymph nodes, bone marrow, and kidneys also were affected. Amyloid-like material that was negative for Congo red was present in most of the affected lymph nodes. Congo red–positive amyloid material was noted in spleen, kidneys, liver, and adrenal glands. Neoplastic plasma cells exhibited immunohistochemical reactions for λ-light chain and 3 classes of heavy chain but not for κ-light chain. Nonamyloid deposits were labeled with antisera against λ-light chain and heavy chains. Plasmacytoid cells, which stained positively for IgG, IgM, or IgA, were intermingled in all lesions. Production of 3 types of immunoglobulins may be caused by heavy-chain class switching, constantly occurring in certain proportions.