A vector that expresses the full-length ospA gene from B. burgdogferi in Escherichia coli (EcA) was previously described [25] . To generate the vector pET9cmut OspA that expresses the OspA mutant ( mut OspA), we designed primers to amplify the B. burgdorferi ospA gene lacking the signal sequence and we cloned the PCR fragment into pET9c. The expression vectors were transformed into E. coli BL21 (DE3) pLysS, the recombinant proteins were purified and the endotoxines were removed using the Detoxi-Gel TM Endotoxin Removing Gel (Pierce Biotechnology, Rockford, IL).