Diagnostic possibilities, biomarkers for PTLD
Direct diagnostic tests for microbial nucleic acid and proteins “are promising alternatives for indirect serologic tests,” Dr. Aucott said. For instance, in addition to polymerase chain reaction tests, which “are making advances,” it may be possible to target the B. burgdorferi peptidoglycan for antigen detection.
Researchers have shown that peptidoglycan, a component of the B. burgdorferi cell envelope, is a persistent antigen in the synovial fluid of patients with Lyme arthritis who have been treated with oral and intravenous antibiotics, and that it likely contributes to inflammation.
“Maybe the infection is gone but parts of the bacteria are still there that are driving inflammation,” said Dr. Aucott, also associate professor of medicine at John Hopkins.
Researchers have also been looking at the host response to B. burgdorferi – including cytokines, chemokines, and autoantibiodies – to identify biomarkers for PTLD and to identify patients during posttreatment follow-up who are at increased risk of developing PTLD, with the hope of someday intervening. Persistently high levels of interleukin-23, CCL19, and interferon-alpha have each been associated in different studies with persistent symptoms after treatment, Dr. Aucott said.
In addition, metabolomics research is showing that patients with PTLD have metabolic fingerprints that are different from those who return to good health after treatment, and it may be possible to identify an epigenetic signature for Lyme disease. A project sponsored by the Defense Advanced Research Projects Agency called ECHO (Epigenetic Characterization and Observation) aims to identify epigenetic signatures of exposures to various threats, including B. burgdorferi.
“At the very proximal end of [indirectly testing for host response], there are modifications of the DNA that can occur in response to infectious insults ... and that changed DNA changes RNA expression and protein synthesis,” Dr. Aucott explained. DARPA’s project is “exciting because their goal [at DARPA] is to have a diagnostic test quickly as a result of this epigenetics work.”
Imaging research is also fast offering diagnostic opportunities, Dr. Aucott said. Levels of microglial activation on brain PET imaging have been found to correlate with PTLD, and a study at Johns Hopkins of multimodal neuroimaging with functional MRI and diffusion tensor imaging has shown distinct changes to white matter activation within the frontal lobe of patients with PTLD, compared with controls.
The NASEM workshop did not collect or require disclosures of its participants.