Changes in splenic histology and cytology in mice bearing plasmacytomas.

Studies of immunosuppression in plasmacytoma-bearing mice (PC-mice) yield important information for understanding a variety of immune phenomena. Most investigations of this model system have utilized splenic cells; thus, valid interpretation of much of this data rests on knowledge of the nature of the cells present in the spleens of PC-mice (PC-spleen). Nevertheless, no comprehensive description of PC-spleens has ever been made and is therefore the subject of this report. Major differences exist between normal and PC-spleens. PC-spleens are enlarged and contain an increased number of cells, the greater proportion of which are large in size. On the basis of morphology and expression of cell surface markers the absolute number of B cells and T cells per spleen was found to be normal or somewhat increased in PC-mice. However, the percentage of these cells was decreased due to an increase in other cell types causing changes predominantly in the red pulp of the spleen. The major populations expanded are polymorphonuclear leukocytes and macrophages. The numbers of megakaryocytes, immature precursor cells, and metastatic tumor cells are also increased to a smaller degree. The implications and relevance of these data to studies of PC-induced immunosuppression are discussed.