AbstractObjectiveActivation of macrophages may contribute to increased atherosclerosis and coronary artery disease in systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). Neopterin, a pteridine derivative, is a novel marker of monocyte and macrophage activation that is associated with atherosclerosis and cardiovascular risk in the general population. We examined the hypothesis that macrophage activation is associated with accelerated atherosclerosis in SLE and RA.MethodsWe compared serum neopterin concentrations, adjusted for age, race, sex, and serum creatinine concentration, in patients with SLE (n = 148) or RA (n = 166) and control subjects (n = 177). In patients with SLE or RA, serum neopterin concentrations were then tested for association (adjusted for age, race, sex, serum creatinine, and medication use) with measures of disease activity or damage, inflammatory markers and mediators, and coronary artery calcium measured by electron beam computed tomography.ResultsNeopterin concentrations were significantly higher in patients with SLE (median 8.0, interquartile range [IQR] 6.5–9.8 nmoles/liter) and RA (median 6.7, IQR 5.3–8.9 nmoles/liter) than controls (median 5.7, IQR 4.8–7.1 nmoles/liter), and were higher in SLE patients than in RA patients (all P < 0.001). In SLE, neopterin was significantly correlated with higher erythrocyte sedimentation rate (ESR; P = 0.001), tumor necrosis factor α (P < 0.001), monocyte chemoattractant protein 1 (P = 0.005), and homocysteine concentrations (P = 0.01), but in RA, it was only associated with ESR (P = 0.01). Neopterin was not associated with coronary calcium in either SLE (P = 0.65) or RA (P = 0.21).ConclusionMacrophage activation, reflected by increased serum neopterin concentrations, was increased in both SLE and RA. Neopterin was more robustly associated with atherogenic mediators of inflammation and homocysteine in SLE than in RA, but was not associated with coronary atherosclerosis in either disease.