Pleomorphic forms of Borrelia burgdorferi induce distinct immune responses.

Borrelia burgdorferi is the causative agent of tick-borne Lyme disease. As a response to environmental stress B. burgdorferi can change its morphology to a round body form. The role of B. burgdorferi pleomorphic forms in Lyme disease pathogenesis has long been debated and unclear. Here, we demonstrated that round bodies were processed differently in differentiated macrophages, consequently inducing distinct immune responses compared to spirochetes in vitro. Colocalization analysis indicated that the F-actin participates in internalization of both forms. However, round bodies end up less in macrophage lysosomes than spirochetes suggesting that there are differences in processing of these forms in phagocytic cells. Furthermore, round bodies stimulated distinct cytokine and chemokine production in these cells. We confirmed that spirochetes and round bodies present different protein profiles and antigenicity. In a Western blot analysis Lyme disease patients had more intense responses to round bodies when compared to spirochetes. These results suggest that round bodies have a role in Lyme disease pathogenesis.