This was indeed the case: C5a exhibited inverse correlation to C5aR expression on both neutrophils (p = 0.0036 and Spearman’s Rank correlation coefficient = -0.5928) and monocytes (p = 0.0010 and Spearman’s Rank correlation coefficient = -0.6291) in SF from RA patients. Here, C5AR1 is linked to rheumatoid arthritis.