Can prior infections prime later autoantibody production and does an IgG-positive, IgM-negative, PCR-negative pattern usually suggest past exposure?

Prior infections can leave durable immune signatures and, in some settings, may help initiate or broaden autoreactivity. However, neither post-infectious autoantibodies nor an IgG-positive test pattern alone establishes active autoimmune or infectious disease.

Mechanistic evidence

• Molecular mimicry has the strongest direct human support. Antibodies to EBV EBNA1 can cross-react with the self-protein GlialCAM; Borrelia OspA/LFA-1 T-cell cross-reactivity has also been described in a subset of antibiotic-refractory Lyme arthritis.
• Bystander activation is biologically credible: infection-related cytokine and innate immune activation can activate pre-existing autoreactive lymphocytes without microbial/self-antigen cross-reactivity. Direct prospective human evidence linking this pathway to persistent new autoantibodies remains indirect.
• Tissue injury and epitope spreading provide an additional plausible route. Infection-related damage releases self-antigens in an inflammatory environment, potentially broadening autoreactive responses. These mechanisms support risk or contribution, not proof that a particular infection caused an individual’s autoantibodies or autoimmune illness.
• Longitudinal evidence that EBV seroconversion preceded multiple-sclerosis onset and cohort associations between SARS-CoV-2 and several autoimmune diagnoses support temporal relationships, but do not identify a specific causal mechanism in an individual.

Interpreting IgG-positive, IgM-negative, PCR-negative results

• For Borrelia, persistent IgG can remain for years or decades after eradicated infection; absent IgM makes a recent antibody response less evident. Thus, this pattern favors prior immune exposure probabilistically.
• It does not exclude active Lyme disease: IgG occurs in both current and remote infection, while PCR performance depends on disease stage and sampled tissue. Blood and CSF PCR are generally low-yield; skin or synovial-fluid PCR can be useful in selected presentations.

Bottom line

• Prior infections can plausibly prime autoantibody production—most convincingly through molecular mimicry—but autoantibody positivity is not synonymous with autoimmune disease. IgG-positive/IgM-negative/PCR-negative results more often fit past exposure than active infection, yet require interpretation alongside symptoms, exposure history, manifestation, and appropriately targeted testing.