Elevated C5a plasma levels correlate with the onset of various inflammatory disorders including sepsis, rheumatoid arthritis, acute lung injury, ischaemia-reperfusion injury, allergy and asthma (Guo & Ward, 2005 ▶; Klos et al., 2009 ▶, 2013 ▶), implicating C5a as a causative or exacerbating agent in the pathogenesis of these conditions. This evidence concerns the gene C5AR1 and rheumatoid arthritis.