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Characteristics
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IgM antibody reacts with heavy chain (µ-chain) from the human immunoglobulin IgM. On cryostatic tissue this antibody marks IgM immunoglobulins contained in plasma cells, follicular B cells and dendritic reticular cells. The common feature in plasmacytomas, some leukemias and some B cells lymphomas is the expression of one unique heavy and light chain, therefore, IgM antibody is useful to mark them. On paraffin-embedded tissues, cytoplasm immunoglobulins are stained, for example in myeloma, plasmacytoma and normal plasma cells. Generally membrane bond immunoglobulins, connective tissue or blood vessels bond extracellular immunoglobulinss and immunocomplex can only be shown on frozen tissues. Plasma cells may not be much stained on frozen tissues because immunoglobulins distribute diffusely by their cytoplasm. Immunohistochemistry (IHC) is a complex technique in which immunological and histological detection methods are combined. In general, the manipulation and processing of tissues before immunostaining, especially different types of tissue fixation and embedding, as well as the nature of the tissues themselves may cause inconsistent results (Nadji and Morales, 1983). Endogenous pseudoperoxidase and peroxidase activity or endogenous biotin and alkaline phosphatase activity can cause non-specific staining results depending on the detection system used. Tissues that contain Hepatitis B surface antigen (HBsAg) can produce false positives when using HRP detection systems (Omata et al, 1980). Insufficient contrast staining and/or improper mounting of the sample may influence the interpretation of results.
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