VARIABILITY OF A BACTERIAL SURFACE PROTEIN AND DISEASE EXPRESSION IN A POSSIBLE MOUSE MODEL OF SYSTEMIC LYME BORRELIOSIS

During persistent infection of scid mice with Borrelia turicatae, an a gent of relapsing fever and neuroborrelidsis, there was variation in t he surface proteins the bacteria expressed and in disease manifestatio ns over time. Two serotypes, A and B, were isolated from the mice, clo ned by limiting dilution, and further characterized. The only discerni ble difference between the two variants was in the size of the major s urface protein they expressed: serotype A had a variable major protein (Vmp) of 23,000, and serotype B had a Vmp of 20,000. When other scid mice were inoculated with clonal populations of A and B, the infection s were similar with respect to onset and degree of spirochetemia, invo lvement of the eye and heart, and occurrence of a peripheral vestibula r disorder. However, there were differences between the serotypes in o ther respects: (a) serotype B but not A caused reddened and significan tly enlarged joints, markedly impaired performance on a walking bar, a nd severe arthritis by histologic examination; (b) serotype A but not B invaded the central nervous system during early infection; and (c) s erotype A penetrated monolayers of human umbilical vein endothelial ce lls more readily than did serotype B. The combination of arthritis, my ocarditis, and neurologic disease resembled human Lyme borreliosis. Th e findings indicate that differences in disease expression are determi ned by variable surface proteins of the bacterium and that scid mouse infections with B. turicatae provide a model for the study of the path ogenesis of Lyme borreliosis and other persistent spirochetal diseases .