Authors' contributions
HMS designed the study. PJ assisted in the study design, oversaw the project running and data analysis, and drafted the manuscript. PJ, JZ, IN, and BJ performed the alternative splice variant cloning, sequence analysis, protein expression and purification, and ligand/receptor binding assays. SP performed and analyzed the quantitative PCR experiment. EMP and MF assisted in the study design and coordination, and oversaw the data analysis and drafting of the manuscript. PFS and DC designed and carried out the in vivo arthritis studies. All authors read and approved the final manuscript.