C3 and Arthritis: This study proved that sheep arthritis triggered a robust immune response, as shown by the significantly higher levels of pro-inflammatory cytokines (IL-1α, IL-1β, IL-6 and TNF-α), acute-phase proteins (Fb, Hp, SAA and Cp) and free radicals (NO and MDA) and the significantly lower levels of anti-inflammatory cytokines (IL-10), antioxidants (CAT, GR and GPx) and complements (C3 and C4) in AG compared to CG.