Richard T. Robinson, PhD
Microbiology and Immunology
Medical College of Wisconsin
Research Focus: Cellular Responses to Mycobacterium tuberculosis
PhD: Dartmouth College (2007)
Postdoctoral Training: Trudeau Institute, Saranac Lake, NY
My research program centers on TB Immunology, and comprises two projects: (Project 1) Regulation of TB resistance by IL12RB1, and (Project 2) Regulation of TB Immunopathology by Vitamin D. Summaries of each project are below:
(Project 1) Regulation of TB resistance by IL12RB1. Tuberculosis (TB) is a human disease caused by the bacterial pathogen Mycobacterium tuberculosis (Mtb). In 2015, TB ranked above HIV/AIDs as a leading cause of death worldwide. The gene IL12RB1 regulates human resistance to TB by promoting cytokine (IL12/IL23)-dependent differentiation of naïve TH cells into TH1 and TH17 effectors. TH1 and TH17 cells limit Mtb survival by activating Mtb-infected macrophages and recruiting neutrophils to infected sites. It was established >20 years ago that IL12RB1 is transcribed and translated into IL12Rβ1, a transmembrane receptor on the TH cell surface that binds IL12/IL23, and then complexes with secondary receptors (IL12Rβ2, IL23R) to activate the intracellular signaling cascades that drive TH1/TH17 differentiation. However, we recently demonstrated that IL12RB1 is also transcribed and translated into a second isoform (Isoform 2, or Iso2) that is a secreted potentiator of IL12/IL23 activity. The mechanism whereby Iso2 potentiates IL12/IL23 activity is not known. Here, we propose a research project that will both fill important gaps in our knowledge of IL12RB1 and determine the mechanism of Iso2 potentiation. This project is significant since IL12RB1 regulates multiple immune responses including TB-resistance, and innovative since it will establish a paradigm for how natural soluble cytokine receptors potentiate cytokine activity. The methods and approach we use build on our demonstrated expertise in IL12RB1 molecular biology, immunology and the mouse TB model. There are two Specific Aims (FIGURE 1): (AIM 1) Determine the biochemical mechanism that Isoform 2 enhances IL12/IL23 signaling; (AIM 2) Determine the immunological mechanism that Isoform 2 increases TB resistance. At the end of our studies, we will have extended our basic understanding of IL12RB1 immunobiology in the context of TB, as well as generated novel proteins with potential use as an adjunct TB therapy. Since IL12RB1’s influence extends beyond TB to also include autoimmunity, cancer, and atopic disease, the mechanisms we identify are relevant to these other human diseases.
FIG 1. (LEFT) The prototypical IL12/IL23 signaling pathway, in which cytokine associates with surface IL12Rβ1 (non-signaling) and IL12Rβ2/IL23R (signaling), triggering an intracellular signaling cascade that leads to TH1/TH17 differentiation. (RIGHT) Trans-Chaperoning, which is our proposed mechanism for how Iso2 enhances IL12/IL23 signaling. In this model, extracellular Iso2 associates with cytokine and chaperones it to the cell surface, where the Iso2:cytokine complex comes into contact with IL12Rβ1. IL12Rβ1’s affinity for this complex is greater than its affinity for cytokine alone, leading to prolonged intracellular signaling and enhanced TH1/TH17 differentiation.
(Project 2) Regulation of TB Immunopathology by Vitamin D. There is currently widespread interest in using Vitamin D (VitD) as a host directed therapy to either shorten TB antibiotic treatment (~6 months) or improve antibiotic treatment outcome. VitD is a fat-soluble secosteroid that is acquired through diet and synthesized in the skin following exposure to sun UVB radiation; its mycobactericidal effects have been demonstrated in vitro, both via direct and indirect mechanisms. However strong these in vitro data are, recent large clinical trials demonstrate VitD does not shorten TB patients’ sputum conversion (i.e. the antibiotic treatment period necessary for Mtb to disappear from the sputum). Recently, using the mouse model of TB, we observed that dietary VitD3’s in vivo role during TB is not to kill Mtb; rather, VitD’s in vivo role during TB is to function through hematopoietic lineages to suppress the development of lung immunopathology. This is significant, as TB morbidity/mortality is associated with a failure to resolve lung immunopathology. The mechanism by which dietary VitD3 suppresses TB immunopathology remains unknown. Our research project is filling important gaps in our knowledge of the VitD/TB interaction in vivo and determining the mechanism by which VitD3 suppresses TB immunopathology in the lung. Specifically, are testing the hypothesis that VitD suppresses TB immunopathology by promoting the activity of regulatory T cells (TREG cells). This project is both significant given the global burden of TB and need for host-directed therapies that limit TB immunopathology, innovative given that it shifts our paradigm of VitD’s role during TB. The methods and approach we use build on our demonstrated expertise in immunological assays, the mouse TB model, and use of vitamin D receptor knockout (vdr-/- mice). There are two specific aims (FIGURE 2): (AIM 1) Cytokine expression of granuloma T cells in the absence of VitD signaling. For this, lung sections from Mtb-infected B6 and vdr-/- mice will be stained with fluorescent antibodies specific to TH1, TH17 and TREG lineages; the frequency of each lineage in the granulomas of each group will then be visualized and quantified using laser-scanning cytometry. We will also adoptively transfer vdr-/- T cells into Mtb-infected B6 mice, and subsequently compare their effector gene expression profile to those of B6 T cell controls. (AIM 2) Determine the contribution of TREG cells to VitD3 suppression of TB immunopathology. TREG cells from B6 mice will be purified via FACS (CD4+CD25HI) and adoptively transferred into vdr-/- mice immediately prior to Mtb-infection; a second group of vdr-/- mice will receive non-TREG cells (CD4+CD25LO). At timepoints representing both early- and late-stage TB, the extent of lung pathology in each group will be measured and compared to wild type controls. We will also purify T regs from Mtb-infected vdr-/- mice and compare their function to B6 controls in a classical in vitro suppression assay. At the end of our studies, we will have extended our understanding of VitD3 in the context of TB and as a host-directed therapy for this global disease. This project also has direct translational implications.
FIGURE 2. Proposed model for how VitD suppresses TB immunopathology. Following infection, naïve TH cells differentiate into TH1/TH17 effectors, and TREG cells. TH1/TH17 effectors limit Mtb burden, but are also capable of further expanding into cells that cause lung pathology. The expansion of pathological TH1/TH17 cells is suppressed by TREG cells via a VitD-dependent mechanism. AIM 1 will quantify the extent of TH1/TH17 expansion in B6 and vdr-/- granulomas, and track development of vdr-/- TH cells following adoptive transfer into Mtb infected Thy1 congenics. AIM 2 will test if adoptive transfer of B6 TREG cells into vdr-/- mice rescues mice from TB immunopathology, and if TREG cells from Mtb-infected vdr-/- mice are less function compared to B6 controls.
February 2015 Infection and Immunity
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November 2012 Infection and Immunity
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