Mechanisms of Pain and Immune Processes

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Overview: This translational research program addresses molecular and pathophysiological processes of nociceptive transmission and new ways to investigate chronic pain, autoimmune conditions, infectious diseases and their intersection in human patients. Chronic neuropathic pain can affect any part of the body and can occur due to a variety of insults, infections, and 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. Autoantibodies are known culprits in certain large fiber peripheral neuropathies such as in paraneoplastic disorders. 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, which are expressed in mammalian cells. This assay is called luciferase immunoprecipitation systems (LIPS) and we have multiple published papers showing that LIPS can robustly and sensitively measure antibodies in serum, plasma, cerebrospinal fluid or saliva. The goals of this research are to understand (a) the 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. In this project an autoimmune hypothesis is explored. The assay methodology we established has great versatility due to its sensitivity, modularity, and use of recombinant DNA methodology to generate protein antigen tracers. Our early investigations evaluated a range of diseases and disorders that antibodies play a role in, including infectious diseases, with and without nervous system involvement, autoimmune disorders, which may have nervous system symptomology in subsets of patients, and other types of screening and methodological variants. In many neural autoimmune disorders the major autoantigens are frequently plasma membrane receptors or ion channels. We have generated several such probes for neuropathic pain disorders, notably the beta-adrenergic receptor and a potassium channel based on published reports, and are currently testing to determine if the LIPS assay can detect antibodies to these proteins in appropriate patients. We completed a study on shingles or herpes zoster that can evolve into a painful neurological disorder called post-herpetic neuralgia (PHN). We detected some neutralizing anti-cytokine autoantibodies in a subpopulation 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. One of the most compelling aspects of this project is the progressive layering and evolution of the datasets and their uses. 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 and our autoantigen-based classification of patients with Lupus Erythematosis. 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, saliva-based assays for many types of human diseases or assessment of vaccine immune status for large or vulnerable populations of people or the pediatric population. Eventually, full multiple antigen profiling can be implemented to obtain a deeper level of understanding of many complex human disease states.