Laboratory analyses of human body fluids play an important role in clinical diagnosis. This thesis comprises projects in which various immune assays have been developed and evaluated as complement diagnostics in both plasma and cerebrospinal fluid (CSF). Various methods have been used, such as ELISA, Western blot, flow cytometry, and xMAP technology.

In paper 1, we monitored complement parameters in EDTA-plasma and CSF from patients with suspected neuroborreliosis (NB) by using in-house sandwich ELISAs.  We found significantly elevated levels of C1q, C4, C3, and C3a in CSF, but not in plasma, suggesting that complement plays a role in the intrathecal immune response in NB.

Complement is a main player in early inflammation, and in paper 2, we investigated the role of complement activation in phagocytosis and the release of cytokines and chemokines in response to two clinical isolates: Borrelia afzelii K78 and Borrelia garinii LU59. Our results show that complement activation plays an important role in the initial process of phagocytosis, but not in the subsequent cytokine release that occurs in response to live Borrelia spirochetes. C1q, a valuable biomarker of disease activity in systemic lupus erythematosus (SLE), can be quantitated using a number of different immunochemical techniques.

In paper 3, we developed and validated a magnetic bead-based immunoassay for quantifying C1q in EDTA-plasma and CSF. In contrast to soluble immunoprecipitation assays such as nephelometry and turbidimetry, this new assay was not hampered by the interaction between C1q and detecting antibodies. The novel assay was shown to give a clear correlation between nephritis and SLEDAI score in SLE.

Warfarin is a commonly used but complicated treatment in patients with thrombosis. It reduces the function of vitamin K-dependent coagulation proteins, including protein S, which is a ligand for C4b-binding protein (C4BP). In paper 4, we demonstrated a decrease in various isoforms of C4BP that resulted in a strong complement activation in patients treated with warfarin, but not in patients treated with other anticoagulants.

Taken together, the results from the papers included in this thesis stress the importance of validated assays with high sensitivity and specificity in enabling accurate diagnosis in patients with various inflammatory diseases.