OBJECTIVE: Novel activation products that are stable and minimally susceptible to in vitro artefacts have recently been described in the classical complement pathway. The present study assessed circulating levels of these products, i.e., covalent complexes between the recognition molecule of the classical pathway ( @entity6300 ) and activated @entity10287 , in plasma samples from @entity1 with @entity309 ( @entity309 ) to establish the relationship between these levels and the clinical and immunologic parameters in these @entity1 . METHODS: @entity6300 -C4 levels were measured in plasma samples from 41 @entity1 with active @entity309 and 43 @entity1 with inactive @entity309 . These levels were related to other complement activation products and to disease activity according to the Disease Activity Score in 28 joints (DAS28), using Spearman's rank correlations. RESULTS: @entity6300 -C4 plasma levels were significantly higher in @entity1 with active @entity309 as compared with @entity1 with @entity309 in clinical remission (median 3.3 arbitrary units [AU], range 0.4-13.4 versus 1.7 AU, range 0.2-5.5; P=0.0001), suggesting that activation of the classical complement pathway reflects disease activity. This was supported by a significant correlation between @entity6300 -C4 levels and the DAS28 (r=0.398, P=0.0002). Levels of other complement activation products, such as activated @entity10287 ( @entity10605 ), were also significantly elevated in @entity1 with active disease compared with @entity1 with inactive disease (P=0.03), and were correlated with @entity6300 -C4 levels (r=0.329, P=0.002). Levels of @entity6300 -C4 complexes were higher in synovial fluid samples than in plasma samples from the 4 @entity1 tested. CONCLUSION: Systemic complement activation via the classical pathway in @entity1 with @entity309 correlates with disease activity. These results indicate that @entity6300 -C4 complexes may be used as a biomarker for @entity309 .

Evaluation of classical complement pathway activation in XXXX : measurement of @entity6300 -C4 complexes as novel activation products.

@entity1 :: ('9606', 'Species') :: ['patients'] @entity6300 :: ('712', 'Gene') :: ['C1q'] @entity10605 :: ('720;721', 'Gene') :: ['C4b/c'] @entity309 :: ('MESH:D001172', 'Disease') :: ['rheumatoid arthritis', 'RA'] @entity10287 :: ('720', 'Gene') :: ['C4']
@entity309 :: (MESH:D001172,Disease) :: ['rheumatoid arthritis']
