Antigen-induced differential gene expression in lymphocytes and gene expression profile in synovium prior to the onset of arthritis

To explore early signature genes playing critical roles in the initial steps in an autoimmune murine model of rheumatoid arthritis (RA) (proteoglycan (PG)-induced arthritis; PGIA), we performed gene expression profiling of 'arthritogenic' spleen cells stimulated with cartilage PG, and compared them to differentially expressed genes, identified in joints prior to the onset of arthritis, and then in the acute and chronic phases of the disease. A total of 280 genes were up-regulated and 226 genes were suppressed in in vitro PG-stimulated lymphocytes at a minimum of 2-fold expression change. Functional gene classification identified several major clusters of biological activity. Expression of immunoglobulin genes (66 transcripts) was downregulated by ∼3.7-fold, whereas most of the other genes with immune/ inflammation-associated functions such as interleukins (IL-1, -2, -4, -6, -10, -12, -16, -17), chemokine receptors and their ligands (Cxcl1, Ccl2, 7, 8, 9, 10, 22, Ccr2, Ccr5), and major components of the complement cascade were upregulated. Using adoptive disease transfer with stimulated lymphocytes into SCID mice, followed by gene expression profiling of SCID paws, indicated that 37 genes were differentially expressed in yet non-inflamed (pre-arthritic) paws; these genes were related mostly to chemokine, IFN-γ and TNF-α signaling. However, the majority of differentially expressed immune response-related genes were silent in pre-arthritic joints, and only 12 genes were found differentially expressed both in antigen (PG)-stimulated lymphocytes and in the synovium prior to the onset of arthritis. Most of these 'arthritis-initiation' genes belonged to chemokine mediated cell motility. Transcripts of chemokine receptor 5 (Ccr5), chemokine ligand 7 (Ccl7) and IFN-γ-inducible proteins (Ifi47) and GTP-ase 1 were expressed at the highest levels in both antigen-stimulated lymphocytes and pre-inflamed synovium, which suggests a key role of these genes in both lymphocyte maturation and arthritis initiation.