MACROPHAGES EXPOSED TO BORRELIA-BURGDORFERI INDUCE LYME ARTHRITIS IN HAMSTERS

The mechanism(s) by which Lyme arthritis is induced has not been eluci dated. In this study, we showed that macrophages have a direct, effect or role in the pathogenesis of Lyme arthritis. Severe destructive arth ritis was induced in recipients of macrophages obtained from Borrelia burgdorferi-vaccinated and nonvaccinated hamsters exposed to Formalin- inactivated B. burgdorferi in vitro and then challenged with the Lyme spirochete. Swelling of the hind paws was detected within 8 h of infec tion, increased rapidly, and peaked at 21 h. This initial swelling dec reased, and by day 4 only slight swelling was detected. Severe swellin g of the hind paws was detected 8 days after infection acid increased rapidly, with peak swelling occurring on day 11. Histopathologic exami nation affirmed that macrophages exposed to Formalin-inactivated spiro chetes induced a severe destructive Lyme arthritis. The onset and seve rity of the severe destructive arthritis were dependent on the number of macrophages transferred. By contrast, macrophages not exposed to Fo rmalin-inactivated B. burgdorferi failed to induce severe destructive arthritis in recipients after challenge with B. burgdorferi. Similarly , severe destructive arthritis was not detected in recipients of macro phages injected with spirochetal growth medium. Our results also showe d that transferred macrophages could not protect hamsters from infecti on with B. burgdorferi, as spirochetes were readily recovered from the ir tissues when cultured. These findings demonstrate that macrophages exposed to B. burgdorferi are directly involved in the induction of Ly me arthritis.