Emergence of the acquired immune response only after week 3 PI. C6 (VlsE) serum-antibody levels as a function of time PI, as measured by C6 ELISA in B. burgdorferi-infected animals. A. DR50, B. EL81, C. EL66, D. EP51, E. DH50, F. CH82, and G EJ86. The dotted line represents the cut-off value obtained as described in Materials and Methods. Data represents mean ± SD of triplicate determinations.