On further examination, BLT1-expression on neutrophils was found crucial for their release of the pro-inflammatory cytokine, IL-1β, into the joint which induced the production of neutrophil-active chemokines, for example, CXCL1, CXCL5, and CCL9, from resident tissue cells of the joint (33) (the role and impact of IL-1 β in the progression of arthritis in the K/BxN STA model will be discussed in further detail later). This evidence concerns the gene LTB4R and arthritic joint disease.