Can Borrelia infection cause neuroinflammation and loss of self-tolerance?

Borrelia infection—particularly definite Lyme neuroborreliosis—has strong human evidence for provoking CNS immune activation. The broader proposition that it causes clinically meaningful loss of self-tolerance through molecular mimicry or bystander activation remains biologically credible but not established in humans.

Clinical and neuroinflammatory evidence

• Human CSF studies in definite Lyme neuroborreliosis show elevated leukocytes and markedly increased CXCL13, which tracks both intrathecal Borrelia-specific antibody production and CSF leukocyte counts.
• CSF cytokine responses span Th1, Th2, Th9, Th17, and regulatory-T-cell-associated pathways, with elevated B-cell-associated markers across clinical neuroborreliosis subgroups. This supports a broad intrathecal inflammatory and B-cell/Th17-linked response rather than a narrowly restricted immune reaction.
• These findings support infection-associated neuroinflammation during active CNS disease, but do not demonstrate persistent CNS inflammation after microbiologic cure.

Mechanistic interpretation

• Molecular mimicry: Borrelia-reactive antibodies and T-cell responses with neural-antigen reactivity have been reported, making cross-reactivity a plausible route to autoreactive immune responses. However, paired pathogen–self epitope mapping, in-vivo pathogenicity, and evidence that mimicry predominates over other mechanisms are not established.
• Bystander activation: CSF leukocytosis, chemokine induction, and broad cytokine activation could lower activation thresholds for autoreactive lymphocytes. Yet available human data do not distinguish nonspecific bystander activation from antigen-specific responses.
• A single-cell CSF antibody study found antibodies recognizing either Borrelia or CNS/myelin antigens rather than both, compatible with infection-associated autoreactivity that is not necessarily molecular mimicry.

Clinical implications

• Persistent serum or CSF antibodies, including an elevated CSF:serum antibody index, can remain for years after successful treatment and should not alone be interpreted as active infection.

Bottom line

• Borrelia can promote neuroinflammation with strong support; molecular mimicry and bystander activation are plausible mechanisms for impaired self-tolerance, but their causal role in human autoimmune or persistent neurologic disease remains unproven.