Borrelia burgdorferi RevA antigen is a surface-exposed outer membrane protein whose expression is regulated in response to environmental temperature and pH

Borrelia burgdorferi, the causative agent of Lyme disease, produces RevA pr otein during the early stages of mammalian infection. B. burgdorferi appare ntly uses temperature as a cue to its location, producing proteins required for infection of warm-blooded animals at temperatures corresponding to hos t body temperature, but does not produce such virulence factors at cooler, ambient temperatures. We have observed that B. burgdorferi regulates expres sion of RevA in response to temperature, with the protein being synthesized by bacteria cultivated at 34 degreesC but not by those grown at 23 degrees C. Tissues encountered by B. burgdorferi during its infectious cycle vary i n their pH values, and the level of RevA expression was also found to be de pendent upon pH of the culture medium. The cellular localization of RevA wa s also analyzed. Borrelial inner and outer membranes were purified by isopy cnic centrifugation, and membrane fractions were conclusively identified by immunoblot analysis using antibodies raised against the integral inner mem brane protein MotB and outer membrane-associated Erp lipoproteins. Immunobl ot analyses indicated that RevA is located in the B. burgdorferi outer memb rane. These analyses also demonstrated that an earlier report (H. A. Bledso e et al., Infect. Immun. 176:7447-7455, 1994) had misidentified such B. bur gdorferi membrane fractions. RevA was further demonstrated to be exposed to the external environment, where it could facilitate interactions with host tissues.