Cytokines, cytokine receptors and matrix interactions control and regulate the development of the hematopoietic system, normal as well as malignant. IL-6 has been recognized to have a major role in the development of multiple myeloma, although its mode of action is unclear. Preliminary studies indicate co-existence of autocrine and paracrine IL- 6 stimulation and lead us to believe that IL-6 gene expression by myeloma cells is inducible rather than constitutive. Identifying the cytokines which induce IL-6 gene expression by myeloma cells and determining the cells which produce them is one of the goals of this project. Sensitive techniques such as PCR and ELISA will be employed and new techniques developed for single cell analysis. Although myeloma cells produce IL-6 and display IL-6 receptors, their low in vivo proliferative activity and the inability of the cytokine to induce sustained proliferation in vitro suggest that the target cell for IL-6 may be a myeloma precursor cell. To address this hypothesis, methods for purifying the pre-myeloma cells from myeloma patient's blood will be developed. High resolution flow sorting on the basis of phenotypic characteristics reported to be associated with pre-myeloma cells will be used to obtain these cells in high purity. The effects of cytokines on the proliferation and differentiation of these cells into the recognizable monoclonal myeloma cells will be studied using a variety of culture conditions, including co-cultures with cytokine secreting cells. Sophisticated cell cycle analysis techniques like BUdR/IUdR labeling and expression of the Ki-67 antigen will be used to determine proliferation. Morphologic, genetic and phenotypic analysis with the aid of image analysis will help determine differentiation. Examination of the effects of dexamethasone and interferon which are effective in the treatment of myeloma will reveal if they have regulatory effects on the production of cytokines and if resistance to these drugs is a tumor and/or an accessory cell phenomenon. These data, generated with help from the Cores, will elucidate the role of cytokines in the development of multiple myeloma.