We aimed to investigate the role of C3 during chronic infection by L. interrogans strain FIOCRUZ L1-130 (LIC) in C57BL/6 wild-type (WT) and C3 knockout (C3KO) mice, monitored for 15, 30, 60, 90, or 180 days post-infection (d.p.i.). The gene discussed is C3; the disease is infection.