Overview: This translational research program addresses pathophysiological processes related to neuropathic pain and the potential confluence of chronic pain, autoimmunity, infectious diseases, and their intersections in human patients. Chronic neuropathic pain can affect any part of the body and can occur due to a variety of insults, infections, autoimmune or metabolic disorders (e.g., diabetic peripheral neuropathy). We are testing the hypothesis that, in some patients, chronic pain is initiated and/or maintained by immunopathological processes related to autoantibodies generated against proteins in peripheral nerve or Schwann cells or possibly components of the central nervous system. Autoantibodies are known culprits in certain large fiber paraneoplastic peripheral neuropathies and large fibers can also contribute to neuropathic dysesthesias. Where pain is a component, we hypothesize the presence of autoantibodies to proteins found in nerve endings arising from small diameter pain-sensing (nociceptive) C- or A-delta nerve fibers. To test the hypothesis that painful neuropathic conditions have an autoimmune component, we established a sensitive, quantitative, liquid phase luminescence assay that uses recombinant protein antigen-luciferase fusions as tracers obtained after expression in mammalian cells. The goals of this research are to understand (a) potential molecular and cell biological mechanisms underlying human chronic pain disorders, and (b) to use this knowledge to devise new treatments and diagnostics for pain and other disorders to which it can be adapted. The methodology we established, the luciferase immunoprecipitation systems (LIPS) assay, robustly and sensitively detects antibodies in serum, plasma, cerebrospinal fluid, or saliva. Our early investigations evaluated a range of diseases and disorders that antibodies play a role in, including viral and bacterial infections with and without nervous system involvement and autoimmune disorders that have nervous system symptomology in subsets of patients. In many neural autoimmune disorders, the major autoantigens are frequently plasma membrane receptors or ion channels (Burbelo et al., 2016).
Our aim i s to determine if the LIPS assay can detect auto-antibodies to these proteins in appropriate chronic pain patients. For example, we completed a study on shingles (herpes zoster) and patients in which shingles evolved into a painful neurological disorder called post-herpetic neuralgia (PHN). We detected some neutralizing anti-cytokine autoantibodies in a subpopulation of Zoster patients, and, interestingly, all of these had PHN. This is important because it suggests that some patients with PHN may require additional intervention to control the disorder other than just analgesic medications. In a recent publication we demonstrated both HSV1 transcripts and HSV1 antibodies in post-mortem human trigeminal ganglion and whole blood, respectively. The correspondence between titer and transcript was 100%. The fact that we used RNA-seq allowed us to align the HSV1 reads to the HSV1 genome and all of the transcripts aligned with the HSV1 latency associated transcript (LAT), indicating that none of the subjects had viral re-activation at the time of death. We can use this approach as a component in a larger study of headache and migraine. One of the most compelling aspects of this project is its broad applicability and the progressive layering and evolution of the datasets. As we increase the number of test antigens, and assay across conditions and diseases, we assemble comprehensive evaluations of immune and autoimmune responses. This is accomplished by determination of (a) the extent and specificity of immune response to orthologous proteins and protein fragments, (b) overlap in antigen profiles indicative of common denominators or general mechanisms, and (c) antigenicity within an entire signaling pathway involved in inter- or intracellular communication. Examples are the TRIM family of proteins in Sjogren's Syndrome, our autoantigen-based classification of patients with Lupus Erythematosis, and a recent examination of antibodies to oncogene products in HPV driven cancers. An example of a new use for public health monitoring is our earlier demonstration of autoantibody measurements in saliva, which highlights the feasibility of establishing non-invasive assays in vulnerable or pediatric population. Eventually, full multiple antigen profiling can be implemented to obtain a deeper level of understanding of the immune component of many complex human disease states.
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