Complement activation in patients with primary antiphospholipid syndrome.
OBJECTIVE
To investigate the significance of complement activation in patients with primary antiphospholipid syndrome (APS).


METHODS
Thirty-six patients with primary APS, 42 control patients with non-systemic lupus erythematosus (SLE) connective tissue diseases, and 36 healthy volunteers were analysed retrospectively. Serum complement levels (C3, C4, CH(50)) and anaphylatoxins (C3a, C4a, C5a) were examined in all subjects, and serum complement regulatory factors (factor H and factor I) were measured in patients with primary APS. Plasma anticoagulant activity was determined in a mixing test using the activated partial thromboplastin time.


RESULTS
Serum complement levels were significantly lower in patients with primary APS than in patients with non-SLE connective tissue diseases (mean (SD) C3: 81.07 (17.86) vs 109.80 (22.76) mg/dl, p<0.001; C4: 13.04 (8.49) vs 21.70 (6.96) mg/dl, p<0.001; CH(50): 31.32 (8.76) vs 41.40 (7.70) U/ml, p<0.001) or healthy volunteers. Only two healthy subjects with low serum C4 levels showed hypocomplementaemia, whereas most patients with primary APS showed raised serum C3a and C4a. No subjects showed raised C5a. Patients with primary APS with low serum C3 or C4 had significantly higher levels of C3a or C4a than healthy controls. No patients had low serum complement regulatory factors. Among patients with primary APS, hypocomplementaemia was significantly more common in those with high anticoagulant activity than in those with low or normal activity.


CONCLUSIONS
Hypocomplementaemia is common in patients with primary APS, reflecting complement activation and consumption, and was correlated with anticoagulant activity, suggesting that antiphospholipid antibodies may activate monocytes and macrophages via anaphylatoxins produced in complement activation.
Oku
K
K
Department of Medicine II, Hokkaido University Graduate School of Medicine, Sapporo, Japan.
Atsumi
T
T
Bohgaki
M
M
Amengual
O
O
Kataoka
H
H
Horita
T
T
Yasuda
S
S
Koike
T
T
D000293:Adolescent; D000328:Adult; D000368:Aged; D000936:Antigen-Antibody Complex / Q000032:analysis; D016736:Antiphospholipid Syndrome / Q000097:blood / Q000276:immunology*; D001777:Blood Coagulation; D016022:Case-Control Studies; D003167:Complement Activation / Q000276:immunology*; D003176:Complement C3 / Q000032:analysis; D015926:Complement C3a / Q000032:analysis; D003181:Complement C4 / Q000032:analysis; D015934:Complement C4a / Q000032:analysis; D003240:Connective Tissue Diseases / Q000276:immunology; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D018709:Statistics, Nonparametric; D014409:Tumor Necrosis Factor-alpha / Q000097:blood; D055815:Young Adult
D000936:Antigen-Antibody Complex; D003176:Complement C3; D003181:Complement C4; D014409:Tumor Necrosis Factor-alpha; D015926:Complement C3a; D015934:Complement C4a