Non-specific Binding of Mouse Myeloma IgM Immunoglobulins by Human Myelin Sheaths and Astrocytes. A Potential Complication of Nervous System Immunoperoxidase Histochemistry

The immunoreactivity of purified mouse myeloma IgM immunoglobulins (mouse IgM) to human myelin sheaths and astroglial cells was evaluated with the peroxidase-antiperoxidase method on paraffin-embedded tissues from human gliomas and areas of multiple sclerosis, and from normal human cerebrum, spinal cord and spinal nerve roots. The mouse IgM reacted positively with central and peripheral myelin sheaths and, as shown independently by others, with the cytoplasm of neoplastic and reactive astroglia. Parallel immunostaining of successive sections with an anti-glial fibrillary acidic protein (GFAP) serum and/or the anti-Leu 7 monoclonal antibody was of considerable assistance in identifying the immunoreactive elements and in distinguishing specific from non-specific immunostaining of myelin sheaths and astroglia. Pretreatment with normal human serum inhibited the non-specific binding by mouse IgM without altering GFAP and Leu 7 reactivities. The non-specific binding of mouse IgM to human myelin sheaths and astroglia can therefore be overcome, and the specificity of mouse IgM monoclonal antibodies retained, by the parallel immunostaining of successive sections with mouse IgM. If non-specific binding by mouse IgM is found to occur, it can then be inhibited by preincubation with normal human serum without loss of specific antigenicity.