By contrast, serum levels of C4, and more specifically C3, may be elevated in serum of patients with RA by virtue of their being acute-phase reactants (APRs), a phenomenon that has also been described in HCV infection, and used to monitor efficacy of treatment [17]; elevation of complement component APRs might mask more subtle activation due to ICs in the circulation unless specific cleavage products (e.g, C3b and C5a) are also assayed. This evidence concerns the gene C3 and rheumatoid arthritis.