This proposal addresses the cell and molecular biologic basis of why cultured synovial cells from rheumatoid arthritis exhibit a distinctive phenotype characterized by rapid proliferation, stellate morphology, abundant degradative enzymes and the constitutive elaboration of a with variety of proinflammatory cytokines and the more general potential for bidirectional interaction between mesenchyme and the autoimmune response. It is hypothesized that, through cell-cell interactions and the constitutive elaboration of cytokines, these distinctive synoviocytes modulate the afferent portion of an autoimmune response and localize it to the joint. One basis of the proposal is the preliminary observation that a representational difference Library prepared by subtracting non- inflammatory osteoarthritis synoviocyte cDNA from RA synovlocyte cDNA, yielding 44 candidate genes preferentially expressed in RA synoviocytes. Prominent among these genes was SDF-1, a novel member of the CXC chemokine family that supports pre B-cell differentiation. The initial focus of investigation will be characterizing this chemokine to understand its role in synovitis. This and the other genes of the library greatly expand the potential to define this distinctive phenotype. Another preliminary finding is that IL-1 and PMA predominantly induce a striking stellate change in synoviocytes cultured from inflammatory joints, suggesting that the cells originate from the intimal synovial lining cell lineage. This stellate response will be used as a clue to unravel the complex relationships of the sustained alteration in expression of particular genes in inflammatory synovitis. It is proposed to identify the potential role of a given overexpressed gene both by examining the cytoarchitectural localization of the gene product in different disease states and by how the overexpressed genes segregate in cloning experiments designed to separate fibroblastoid cells allocated to the intimal synoviocyte lineage from modulated synoviocytes present in subintimal layers. Lastly, in concert with the other project leaders, the interaction between the mesenchymal elements and localized immune responses in murine models of autoimmunity will be explored with a view to determining whether and how the mesenchyme participates in the reaction of the immune milieu, imprinting the localized immune response in such a way as to enhance the participation of B-cells and reenforce and amplify autoimmunity through B-cell antigen presentation mechanisms.
