Suppression of arthritis with an anti-FR-β monoclonal antibody is perhaps not surprising in view of the fact that FR-β-positive macrophages constitute the most inflammatory subset of this cell type [33], secreting a plethora of inflammatory stimuli (i.e., TNFα, IL-1, IL-6, IL-12, prostaglandins, leukotrienes, and reactive oxygen species) that enhance the inflammatory process including activation of other immune cells [7]. Here, FOLR2 is linked to arthritic joint disease.