Can infections promote autoimmunity through molecular mimicry and bystander activation?

Infections are credible contributors to autoimmune phenomena, but the evidentiary standard for attributing a neural autoantibody response to one specific pathogen is substantially higher than antibody co-positivity.

Clinical and mechanistic evidence

• Molecular mimicry is established in selected post-infectious diseases. In Campylobacter jejuni–associated Guillain–Barré syndrome, bacterial lipooligosaccharides resemble peripheral-nerve gangliosides, and patient antibodies can recognize both structures. In rheumatic fever, group A streptococcal-reactive antibodies and T cells cross-recognize cardiac targets. These are direct human examples in which pathogen–self cross-reactivity can contribute to autoimmune injury.
• Bystander activation is biologically plausible but less directly demonstrated in humans. Infection-related cytokines, antigen-presenting-cell activation, and increased costimulation may nonspecifically activate autoreactive lymphocytes. Tissue injury can expose self-antigens and promote epitope spreading, potentially sustaining an autoimmune response even without direct pathogen–self antigen mimicry.

Interpreting pathogen and neural antibodies

• Concurrent pathogen-directed and neural-target antibodies support an immune association, not pathogen-specific causation. A pathogen-specific IgG result may represent exposure months or years earlier rather than active or temporally relevant infection.
• Herpes simplex encephalitis provides an important clinical precedent: neuronal-antibody seroconversion, particularly NMDAR antibodies, and subsequent autoimmune encephalitis have been reported in roughly one-third of affected patients. This supports a post-infectious relationship, while not establishing molecular mimicry as the universal mechanism.
• Interpretation should incorporate the neural antigen, assay method and titre, clinical syndrome, and paired serum/CSF findings. Isolated serum neural-antibody reactivity may not be clinically pathogenic.

Bottom line

• Infections can promote autoimmunity through proven disease-specific molecular mimicry and plausible inflammatory bystander mechanisms; simultaneous pathogen and neural antibodies indicate association, whereas attributing neural antibodies to a particular pathogen requires longitudinal, compartment-specific, mechanistic, and functional corroboration.