Soluble gp130 is the naturally occurring antagonist of the interleukin‐6 (IL‐6)/soluble IL‐6 receptor (sIL‐6R) complex and selectively inhibits IL‐6 trans‐signaling. Several isoforms of soluble gp130 have been identified, including an autoantigenic form termed gp130‐RAPS (for gp130 of the rheumatoid arthritis antigenic peptide–bearing soluble form) that is present in the serum and synovial fluid of patients with rheumatoid arthritis. The aim of this study was to evaluate the functional properties of gp130‐RAPS.

To define a role for gp130‐RAPS in arthritis, a recombinant version was generated using a baculovirus expression system, and its activities were tested in vitro and in vivo.

Gp130‐RAPS was shown to bind with high affinity to the stable IL‐6/sIL‐6R complex, hyper–IL‐6, and to effectively modulate leukocyte migration in murine acute peritonitis. A single intraarticular injection of gp130‐RAPS suppressed chronic antigen‐induced arthritis in association with a reduction in local activation of signal transducer and activator of transcription 3. Although gp130‐RAPS contains the previously identified autoantigenic sequence Asn‐Ile‐Ala‐Ser‐Phe (NIASF), no increase in the prevalence of anti– gp130‐RAPS antibodies was observed in serum or synovial fluid obtained from patients with rheumatoid arthritis.

The use of inhibitory antibodies to block IL‐6 responses has shown considerable clinical promise. However, the results presented herein suggest that selective targeting of IL‐6 trans‐signaling may represent a viable alternative to this strategy. In this respect, our present results suggest that the soluble gp130 isoform gp130‐RAPS may be useful in the treatment of chronic inflammatory arthritis.