Systemic lupus erythematosus and C1q: A quantitative ELISA for determining C1q levels in serum.

C1q is of interest in systemic lupus erythematosus (SLE) research due to deficiencies in its activity being associated with the disease. Current published protocols for measuring C1q vary greatly in their results and ease of reproducibility. Due to this, average C1q concentrations have been reported between 56 and 276 microg/mL in non-SLE serum. We present an improved method for quantifying C1q concentrations, which employs a sandwich ELISA. This method has improved precision, cost efficiency, up-scaling, reproducibility, and uses significantly lesser volumes of serum sample when compared to RID and other methods for quantifying C1q. We report an average concentration of 113 +/- 40 microg/mL for C1q in non-SLE serum. The assay designed here will be useful in the high-throughput measurement of serum C1q in SLE cases.