Borrelia burgdorferi erpT expression in the arthropod vector and murine host

The expression of a Borrelia burgdorferi gene, erpT, was investigated throu ghout the spirochaete life cycle in the arthropod vector and the murine hos t. Three phage clones from a B. burgdorferi DNA expression library synthesi zed a 30 kDa antigen that was recognized by antibodies in the sera of B. bu rgdorferi-infected mice but not mice hyperimmunized with B. burgdorferi lys ates. Differential antibody binding suggested that this protein was prefere ntially expressed in vivo. This antigen was designated ErpT, based upon 99. 6% homology with the BBF01 sequence in the B. burgdorferi genome. ErpT was not detected on spirochaetes cultured in BSK II medium by indirect immunofl uorescence or in B. burgdorferi lysates by immunoblotting, implying that Er pT is not readily produced in vitro, erpT mRNA was not discernible by North ern blot but was identified by RNA polymerase chain reaction in vitro, indi cating that erpT is expressed at low levels by cultured spirochaetes. erpT expression was then investigated in the vector and mice because B. burgdorf eri do not normally reside in culture medium. RNA polymerase chain reaction and immunofluorescence studies demonstrated that erpT was expressed by a s mall minority of B. burgdorferi (11/500, 2.2%) within unfed ticks and then repressed during engorgement. erpT mRNA or ErpT antibodies were first detec ted in B. burgdorferi-infected mice at 4 weeks, suggesting that erpT was no t expressed in the early stages of murine infection. Then, during persisten t infection, RNA polymerase chain reaction showed that erpT was expressed b y B. burgdorferi within the joints, heart and spleen, but not by spirochaet es in the skin. Immunization of mice with ErpT was antigenic but was not pr otective. These studies demonstrate that B. burgdorferi erpT is differentia lly expressed throughout the B. burgdorferi life cycle, in both the vector and the mammalian host, and is primarily expressed in extracutaneous sites during murine infection.