Can persistent microbial antigen exposure sustain immune signaling and neuroinflammation even when blood PCR is non-establishing?

Persistent or recurrent exposure to microbial antigens can plausibly maintain immune activity and contribute to neuroinflammatory signaling, while a blood PCR that is negative or otherwise non-establishing cannot by itself adjudicate whether infection is active.

Immune and neuroinflammatory mechanisms

• Retained microbial material can sustain innate inflammation without proving ongoing organism replication. In Lyme arthritis, Borrelia burgdorferi peptidoglycan was detected in synovial fluid in 32/34 patients, including after antibiotics, and provoked pro-inflammatory responses in human immune cells, consistent with NOD2-linked cytokine signaling.
• Continued antigen presentation can repeatedly engage T-cell receptors. In chronic viral infection, this may produce persistent activation together with inhibitory-receptor expression, reduced CD8+ T-cell proliferation and cytokine production, and functional exhaustion—not simply greater inflammation.
• In the CNS, microglial pattern-recognition and inflammasome pathways, plus cytokine/chemokine release by microglia and astrocytes, can amplify inflammatory programs. IFN-γ- and IL-17-producing T cells and B-cell antigen presentation/cytokines may further activate glia; regulatory T cells may counterbalance these effects.

Human evidence and diagnostic implications

• Treated HIV studies linking increased TSPO-PET signal with CSF inflammatory, myeloid-activation, and activated CD8+ T-cell markers support persistent CNS immune activation, although these measures are indirect and do not establish cell-specific causation.
• Blood PCR has limited sensitivity for some infections. For suspected Lyme disease, whole-blood/plasma PCR sensitivity is approximately 30–50% in cited U.S. studies because bloodstream spirochetes are sparse and transient. Blood is also not the preferred molecular specimen for Mycoplasma pneumoniae; respiratory NAAT is recommended.

Bottom line

• Persistent antigen exposure is a scientifically supported, pathogen- and context-dependent mechanism for sustained immune signaling that can contribute to neuroinflammation. A non-diagnostic blood PCR should not be interpreted as proof against active infection; testing and interpretation need to match the suspected pathogen, disease site, specimen, and illness timing.