CD40LG and infection: Serum antibody testing, using approved 2-tier Borrelia serology, is highly reliable for evidence of exposure to Borrelia burgdorferi; important caveats include initially false-negative evaluation (when measured within 4‐6 weeks of infection) and that results may take days to return.[8] Public Health Ontario utilizes 2-tier Lyme serology testing with an initial Borrelia VlsE1/pepC10 IgM/IgG enzyme-linked immunosorbent assay; all reactive or indeterminate samples undergo subsequent B. burgdorferi IgM and IgG Western Blot.