Mechanisms of Pain and Immune Processes

Clinical Center

Investigators

Linked publications, trials & patents

Abstract

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 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 fusion proteins 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 disorders. 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. As a result earlier investigations evaluated a range of diseases and disorders that antibodies play a role in including infectious diseases, with and without nervous system involvement, various autoimmune disorders, which may have nervous system symptomology in subsets of patients and other types of screening and methodological variants. In one study, we identified antibodies to interferon gamma in serum from several neuropathic pain patients and then generated a larger panel of anti-cytokine antibody probes, however, antibodies to these other cytokines were not widely represented in the neuropathy patients. Extending testing of the panel to another patient population revealed that anti-interferon gamma antibodies play a role opportunistic infections and this collaborative research work defined a new mechanism of disease in certain patient populations. 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 this protein in appropriate individuals. We are currently working a PNS infectious disease disorder, shingles or herpes zoster, that can evolve into a painful neurological manifestation called post-herpetic neuralgia (PHN). We detected some patients with neutralizing anti-cytokine autoantibodies and, interestingly, all of these had PHN. This suggests that some patients with PHN may require additional intervention to control the disorder other than just pain 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. An example is the antigenicity of the TRIM family of proteins in Sjogren's Syndrome. Another example is a new autoantigen-based classification of patients with Lupus Erythematosis that we demonstrated by multiple autoantigen profiling. 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. Saliva-based monitoring could be applied to determinations 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.