CXCL8 and rheumatoid arthritis: Neutralization of CD13 by WM15, a monoclonal antibody specific for CD13, significantly inhibited the secretion of key proinflammatory mediators, such as MCP-1/CCL2, IL-6, and IL-8/CXCL8, in an RA ST organ culture ex vivo assay (6, 8).