<i>Borrelia burgdorferi</i> sensu lato Employs Several Escape Mechanisms to Bypass the Human Defense System

Lyme borreliosis (LB), caused by Borrelia burgdorferi sensu lato (Bbsl) through Ixodes tick bites, presents diverse clinical manifestations and may lead to persistent symptoms. This review summarizes current knowledge on the pathogen-host interactions and immune responses. Early infection can be influenced by tick saliva, which suppresses local host defense and promotes spirochete survival, and by pattern recognition receptors activating proinflammatory cascades. Bbsl employs a variety of immune evasion strategies, notably impairing antigen presentation-through disruption of MHC II and IFN-γ pathways-and continuously varying surface antigens to hinder long-lasting antibody formation. Autophagy plays a central role in modulating inflammation and T helper 17 adaptive immune responses, representing an underappreciated mechanism potentially influencing disease outcome. Adaptive immunity in LB is characterized by robust but often dysregulated humoral and cellular responses, with transient germinal centers and enduring IgM production contributing to incomplete pathogen clearance. Persistent immune defects include impaired long-term B cell memory, suppressed T cell activation, and ongoing immunosuppression after pathogen clearance. Similar patterns are observed in other postinfectious fatigue syndromes. Despite advances, gaps remain in understanding mechanisms of Bbsl persistence and the immunopathology underlying chronic disease, challenging diagnosis and therapy. Emerging molecular and cellular approaches offer new avenues to address immunity, diagnostics, and prevention. A multidisciplinary effort will be needed to improve long-term patient outcomes in the evolving epidemiology of LB.