Monoclonal antibodies Ki-B3 and Leu-M1 discriminate giant cells of infectious mononucleosis and of Hodgkin's disease.

In infectious mononucleosis (IM), the involved lymphatic tissue may contain large blasts which are generally referred to as Hodgkin cell-like cells when mononuclear and as Sternberg-Reed cell-like cells when multinuclear. The resemblance of these reactive cells to true Hodgkin and Sternberg-Reed cells constitutes a major differential diagnostic problem. In this paper, we report a study of 20 cases of Hodgkin's disease (HD); five of nodular sclerosis and 15 of mixed cellularity type) and of 20 clinically and serologically confirmed cases of IM with the aim of developing immunohistologic criteria for their reliable differentiation. Routinely processed paraffin sections were subjected to the immunoperoxidase reaction using the monoclonal antibodies Leu-M1 (anti-CD15) and Ki-B3. The subcellular distribution of the immunoreactivity to Ki-B3 was controlled at the electron microscopic level. In all cases of HD, many Hodgkin and Sternberg-Reed cells were found to be positive for Leu-M1, whereas the same cells were invariably negative for Ki-B3. By contrast, cells similar to Hodgkin and Sternberg-Reed cells in IM were consistently negative for Leu-M1. The majority of these cells reacted positively for Ki-B3. The results imply that immunohistochemical application of these two antibodies facilitates a clear-cut discrimination of true Hodgkin and Sternberg-Reed cells from similar cells of IM.