Anti-serum amyloid component P antibodies in patients with systemic lupus erythematosus correlate with disease activity.

OBJECTIVE To determine the presence of raised titres of anti-serum amyloid P component (SAP) antibodies in patients with systemic lupus erythematosus (SLE) and to evaluate their correlation with clinical disease by the SLEDAI and clinical manifestations. METHODS 452 samples were screened for raised anti-SAP antibody titres by an ELISA. Clinical measures and SLEDAI scores were independently reviewed from medical records. 21 serial samples from 7 patients with SLE were assessed for a change in anti-SAP antibody titres after treatment. RESULTS Raised anti-SAP antibody titres were detected in 145/328 (44%) SLE samples. In 112 randomly selected samples, 69/112 (62%) patients had raised anti-SAP antibodies and anti-dsDNA antibody titres, whereas only 32/112 (28%) had raised anti-dsDNA antibody titres without raised anti-SAP antibody titres. The mean titre of anti-SAP antibodies in patients with active disease was higher than in patients with inactive disease and controls. SLEDAI scores, assessed in 54 patients, were raised in 26/31 (84%) patients with raised anti-SAP antibody titres. A SLEDAI score >or=8 was found in 16/31 (52%) patients with raised anti-SAP antibody titres but in only 5/23 (22%) patients without raised titres. No specific pattern of disease was detected in patients with or without raised titres of anti-SAP antibodies. Serial sampling from patients with active SLE and raised anti-SAP antibody titres showed that anti-SAP antibody titres decreased after treatment and correlated with clinical improvement. CONCLUSION Raised anti-SAP antibody titres detected in patients with SLE correlate with disease activity and decrease with improvement of clinical disease, and thus may serve as an additional prognostic marker.