The long ospC operator version more effectively reduces the activity of a fused flaB promoter in response to treatment with OspC MAb. Subgroups of 10 SCID mice were inoculated with the clone Bp-C/1, Bp-C/2, Co1-Bp-C/1, Co1-Bp-C/2, Co2-Bp-C/1 or Co2-Bp-C/2. Three weeks later, five mice from each subgroup received a single dose of 100 μg of either OspC MAb or purified murine IgG as a control. One week later, mice were euthanized; RNA was extracted from joint specimens harvested from the 30 IgG-treated mice and from the 20 mice infected with the Co1-Bp-/1, Co1-Bp-C/2, Co2-Bp-C/1, or Co2-Bp-C/2 bacteria and treated with OspC MAb. RNA samples were quantified for flaB and ospC expression by RT-qPCR. Data are presented as ospC transcripts per 1000 flaB mRNA copies in three groups by combining the subgroups Bp-C/1 and Bp-C/2, Co1-Bp-C/1 and Co1-Bp-C/2, and Co2-Bp-C/1 and Co2-Bp-C/2. The Bp-C/1 and Bp-C/2 bacteria were cleared by OspC MAb; therefore no expression data were obtained from this treatment.