J. Zwirner et al., A NOVEL ELISA FOR THE ASSESSMENT OF CLASSICAL PATHWAY OF COMPLEMENT ACTIVATION IN-VIVO BY MEASUREMENT OF C4-C3 COMPLEXES, Journal of immunological methods, 186(1), 1995, pp. 55-63
Measurements of complement split products by enzyme-linked immunosorbe
nt assays (ELISA) are well established for the assessment of in vivo c
omplement activation. We have combined two monoclonal antibodies (mAb)
with specificities for C3b/iC3b/C3dg (mAb I3/15) and C4/C4b/C4d (mAb
M4d2), respectively, in a sandwich ELISA to quantitate C4-C3 complexes
as an indicator of complement activation. Serum incubated with heat a
ggregated IgG (HAG) was used as a standard and the C4-C3 levels expres
sed as mu g equivalent HAG/ml (mu g HAG-equ/ml). Normal values of C4-C
3 complexes in plasma (EDTA) of healthy probands (n = 11) were 6.3 mu
g HAG-equ/ml +/- 1.5 (mean +/- 1 standard deviation (SD), with a range
from 3.6 to 9.1). In patients with systemic lupus erythematosus (SLE,
n = 23) C4-C3 values were clearly elevated (48.8 mu g HAG-equ/ml +/-
52.9, range 7.5-184.7) as compared to samples from patients with idiop
athic hypertension (IDH, n = 10) (6.5 mu g HAG-equ/ml +/- 1.7, range 4
.1-9.4). For SLE patients C4-C3 levels significantly correlated with v
alues for C3b/iC3b/C3d (r = 0.69, p < 0.001) and C3 containing immune
complexes (r = 0.68, p < 0.001), but not with the C4d fragment (r = 0.
26). C4-C3 levels of 96% of the studied SLE patients were increased mo
re than 2 SD above the normal mean as compared to 74% of C4d and activ
ated C3 values, respectively. Serum treated with zymosan as an activat
or of the alternative pathway of complement did not exhibit higher C4-
C3 values. These results demonstrate that the quantitation of in vivo
generated C4-C3 complexes by ELISA provide a novel, sensitive paramete
r for classical pathway of complement activation.