Immunological Responses to the Relapsing Fever Spirochete Borrelia turicatae in Infected Rhesus Macaques: Implications for Pathogenesis and Diagnosis

Abstract

The global public health impact of relapsing fever (RF) spirochetosis is significant, since the pathogens exist on five of seven continents. The hallmark sign of infection is episodic fever and the greatest threat is to the unborn. With the goal of better understanding the specificity of B-cell responses and the role of immune responses in pathogenicity, we infected rhesus macaques with Borrelia turicatae (a new world RF spirochete species) by tick bite and monitored the immune responses generated in response to the pathogen. Specifically, we evaluated inflammatory mediator induction by the pathogen, host antibody responses to specific antigens, and peripheral lymphocyte population dynamics. Our results indicate that B. turicatae elicits from peripheral blood cells key inflammatory response mediators (interleukin-1β and tumor necrosis factor alpha), which are associated with preterm abortion. Moreover, a global decline in peripheral B-cell populations was observed in all animals at 14 days postinfection. Serological responses were also evaluated to assess the antigenicity of three surface proteins: BipA, BrpA, and Bta112. Interestingly, a distinction was observed between antibodies generated in nonhuman primates and mice. Our results provide support for the nonhuman primate model not only in studies of prenatal pathogenesis but also for diagnostic and vaccine antigen identification and testing.

Characterization of Immunological Responses toBorreliaImmunogenic Protein A (BipA), a Species-Specific Antigen for North American Tick-Borne Relapsing Fever

“…We did not assess B. hermsii , because the surface localization of BipA in this species was previously demonstrated through proteinase K assays ( 37 ). Since proteinase K is a serine protease incapable of penetrating the outer membrane of Borrelia ( 38 ), detection of the periplasmic FlaB was performed to ensure the integrity of the bacterial outer membrane ( 35 , 38 – 40 ). The incubation of cells with increasing concentrations of proteinase K (0, 5, 50, and 200 μg mL −1 ) for 15 min resulted in the degradation of BipA, while FlaB remained intact ( Fig.…”

“…We used murine, canine, and nonhuman primate (NHP) serum samples from previous work ( 27 , 34 , 35 , 41 ) and generated additional murine serum samples by infecting animals by tick transmission or needle inoculation ( Table 1 ). Within 5 to 7 days after feeding ticks on mice, we visualized B. turicatae 91E135 or B. parkeri SLO in the blood.…”

“…To assess if the species-specific immunological responses toward BipA occur in other mammals, serum samples from canines and nonhuman primates experimentally infected with B. turicatae were used ( 27 , 34 , 35 ). Serum samples from domestic dogs infected with B. turicatae for 54 days had at least 4-fold higher antibody titers toward Bt -rBipA than Bp -rBipA and 8-fold higher titers than Bh -rBipA ( Table 3 ).…”

“…The human serum sample origins and descriptions are summarized in Table 4 . Domestic dog, rhesus macaque, and murine serum samples originated from prior animal studies ( 27 , 34 , 35 , 41 ), and Table 1 summarizes the origin of serum samples used in this study. To infect mice with B. hermsii , sixteen female ICR mice were inoculated by intraperitoneal needle injection with ~1 × 10 7 cells of the HCT-4 isolate ( 29 ).…”

“…To test the antigenicity of rBipA, we evaluated murine serum samples that were generated by needle-inoculating animals or infecting them by tick bite. We also assessed domestic dogs and rhesus macaque serum samples generated from previous work ( 27 , 35 ). A cohort of human LD-positive serum samples was also tested ( 36 ).…”