The present invention is based on two important experimental observations: The first observation is that increased extracellular concentrations of ionized calcium are found in erosive arthritis and stimulate monocytic IL-1β release via the CaSR and GPRC6A. Simultaneous stimulation of monocytes with calcium ions and selected TLR ligands results in a 20-fold increased IL1β response compared to lipopolysaccharide (LPS) alone. During the crosstalk between GPCR and TLR signaling, phospholipase C is activated, which triggers calcium dependent potassium channels, resulting in potassium efflux, caspase-1 activation and IL-1β release. The amplification of IL1β secretion at sites of locally increased calcium ion concentrations aggravates rheumatoid arthritis. The second important observation is that both CaSR and GPRC6A, are highly expressed in the synovial membrane of patients with rheumatoid arthritis, but expression of GPRC6A, but not of CaSR, is lower in patients with osteoarthritis (s. FIG. 1). The latter is generally not accompanied by inflammation. Thus, expression of GPRC6A appears to be upregulated in chronic inflammatory situations. Based on these experimental observations the invention provides a method and compositions for the identification of agents that have a potential effect against chronic inflammatory conditions, in particular erosive arthritis and atherosclerosis.
