Activation of the reward system boosts innate and adaptive immunity

Journal name:
Nature Medicine
Volume:
22,
Pages:
940–944
Year published:
DOI:
doi:10.1038/nm.4133
Received
Accepted
Published online

Positive expectations contribute to the clinical benefits of the placebo effect1, 2. Such positive expectations are mediated by the brain's reward system3, 4; however, it remains unknown whether and how reward system activation affects the body's physiology and, specifically, immunity. Here we show that activation of the ventral tegmental area (VTA), a key component of the reward system, strengthens immunological host defense. We used 'designer receptors exclusively activated by designer drugs' (DREADDs) to directly activate dopaminergic neurons in the mouse VTA and characterized the subsequent immune response after exposure to bacteria (Escherichia coli), using time-of-flight mass cytometry (CyTOF) and functional assays. We found an increase in innate and adaptive immune responses that were manifested by enhanced antibacterial activity of monocytes and macrophages, reduced in vivo bacterial load and a heightened T cell response in the mouse model of delayed-type hypersensitivity. By chemically ablating the sympathetic nervous system (SNS), we showed that the reward system's effects on immunity are, at least partly, mediated by the SNS. Thus, our findings establish a causal relationship between the activity of the VTA and the immune response to bacterial infection.

At a glance

Figures

  1. Activation of VTA neurons with DREADDs stimulates reward circuitry and behavioral responses.
    Figure 1: Activation of VTA neurons with DREADDs stimulates reward circuitry and behavioral responses.

    (a) Schematic representation of the experimental design—including a depiction of the viral constructs used for Cre-dependent expression of DREADDs and for expression of mCherry, and the representation of a DREADD on the cell-surface membrane. VTA act., activated VTA. (b,c) Representative images of a wide-angle view (top) and a higher-magnification view of the boxed area (bottom) of the virus infection site (b) and quantification of the fraction of mCherry+TH+ cells among the total number of TH+ cells (n = 3 mice) (c). In b, dashed lines outline the VTA, as indicated in the Allen Brain Atlas depiction of the VTA. Viral expression is indicated by mCherry fluorescence (red), co-localized with the VTA TH+ neurons (green). Scale bars, 0.5 mm (b, top) and 100 μm (b, bottom). (d,e) Representative images showing staining of c-Fos (green) and mCherry (red) in the VTA 90 min after activation (d) and quantification of c-Fos staining in virus infected cells (n = 3 mice per group) (e). In d, arrowheads indicate neurons co-labeled for c-Fos and mCherry. Scale bar, 100 μm. (f) Schematic representation of the CPP paradigm (Online Methods). (g,h) A heat map aggregating the location of all mice in the control (top) or VTA-activated (bottom) mouse group in the CPP arena during the test session (day 4) (g) and quantification of the proportion of time spent in the conditioned chamber on the test session (day 4) relative to that on the pre-test (day 1) (n = 8 mice per group) (h). In g, the color gradient indicates areas where the mice spent less time (blue) and areas where the mice spent more time (red). Arena width is 35 cm. Throughout, data are represented as mean ± s.e.m. *P < 0.05, ***P < 0.001; by unpaired two-tailed Student's t-test.

  2. Activation of VTA neurons improves the innate immune response to E.coli.
    Figure 2: Activation of VTA neurons improves the innate immune response to E.coli.

    (a) Schematic illustration of the experimental design. (b,c) Representative dot plot of CD11b+GFP+ cells (control for GFP baseline levels, as identified in mice that were infected with nonfluorescent E. coli, is provided in Supplementary Fig. 7) (b) and quantification of CD11b+GFP+ cells (control, n = 4 mice; VTA-activated, n = 6 mice) (c). Numbers indicate the percentage of CD11b+GFP+ cells. Controls are mice infected with the sham virus and thus express only the fluorescent reporter in their VTA TH+ neurons, i.e., there is no VTA activation. (d) Schematic representation of the ex vivo experiments. (e,f) Phagocytosis analysis using FITC-conjugated OVA in DCs (CD11c+; control, n = 4 mice; VTA-activated, n = 5 mice) (e) and macrophages (CD11b+F4/80+; control (no VTA activation), n = 4 mice; VTA-activated, n = 5 mice) (f). MFI, mean fluorescence intensity. (g,h) Representative images of agar plates showing the number of E. coli colonies remaining after the bacterial killing assay in monocytes and macrophages (CD11b+F4/80+) isolated from VTA-activated mice and controls (g) and quantification of remaining E. coli colonies following incubation with monocytes and macrophages derived from VTA-activated or control mice (n = 5 mice per group) (h). Scale bar, 40 mm. (i) Bacterial load in the liver of VTA-activated mice, as determined by spectroscopy and presented as percentage of bacterial load, as compared to that in control mice (n = 7 mice per group). Throughout, data are represented as mean ± s.e.m. from two independent experiments. *P < 0.05, **P < 0.01; by unpaired two-tailed Student's t-test.

  3. Activation of VTA neurons increases the adaptive immune response to E. coli challenge.
    Figure 3: Activation of VTA neurons increases the adaptive immune response to E. coli challenge.

    (a) Schematic representation of the experimental design. (b) Representative example of changes in splenic B cell abundance obtained by CyTOF analysis, reported as percentage (%) of sample (n = 5 mice per group). Box plots denote median and inter-quantile range; whiskers are 1.5 the inter-quantile range size. (c) Quantification of E. coli–specific IgM concentrations, as measured by ELISA, in the sera of VTA-activated and control (no VTA activation) mice (results are presented as percentage optic density (%OD); n = 6 mice per group). (d) IFN-γ and IL-4 levels in splenic T cells from VTA-activated and control mice, as determined by ELISA (VTA-activated, n = 3 mice; control, n = 4 mice). (e) IgG expression, as determined by ELISA, on splenic B cells derived from mice 7 d after they were injected with E. coli and exposed ex vivo to E. coli (n = 4 mice per group). (f) IFN-γ levels in T cells derived from mice 7 d after E. coli injection, as determined by ELISA. Splenic T cells were isolated and then incubated ex vivo with E. coli–infected macrophages (n = 4 mice per group). (g) Schematic illustration for the DTH experimental design. (h,i) Representative image of a control mouse (infected with the sham virus) and a VTA-activated mouse, showing DTH-induced tissue swelling (as indicated by the dashed line) (h) and quantification of tissue swelling (control, n = 7 mice; VTA-activated, n = 8 mice) (i). Scale bar, 3 mm. (j) IFN-γ levels in T cells from lymph nodes adjacent to the E. coli injection site (n = 7 mice per group). Throughout, data are represented as mean ± s.e.m. from two independent experiments. **P < 0.01; ***P < 0.001; by unpaired two-tailed Student's t-test.

  4. The effects of VTA activation on the immune system are partly mediated by the sympathetic nervous system.
    Figure 4: The effects of VTA activation on the immune system are partly mediated by the sympathetic nervous system.

    (a) Schematic depiction of the experimental design. (b) Analysis of norepinephrine content in the spleens of 6-OHDA-treated mice as compared to saline-injected controls (n = 4 mice per group). ****P < 0.0001 by unpaired two-tailed Student's t-test. (c) Ex vivo E. coli killing assay, as determined with four groups of mice: two with intact SNS (saline-treated VTA-activated and control) and two groups in which the SNS is disrupted (6-OHDA-treated VTA-activated and control). The number of remaining bacteria following incubation of monocytes and macrophages derived from each experimental group with E. coli (n = 3 mice per group). *P < 0.05 by two-way analysis of variance (ANOVA). Results shown are for one of two independent experiments. Throughout, data are represented as mean ± s.e.m.

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Author information

  1. These authors jointly directed this work.

    • Shai S Shen-Orr &
    • Asya Rolls

Affiliations

  1. Department of Immunology, Rappaport Faculty of Medicine, Technion–Israel Institute of Technology, Haifa, Israel.

    • Tamar L Ben-Shaanan,
    • Hilla Azulay-Debby,
    • Tania Dubovik,
    • Elina Starosvetsky,
    • Ben Korin,
    • Maya Schiller,
    • Nathaniel L Green,
    • Yasmin Admon,
    • Fahed Hakim,
    • Shai S Shen-Orr &
    • Asya Rolls
  2. Center of Science and Engineering of Neuronal Systems, Rappaport Faculty of Medicine, Technion–Israel Institute of Technology, Haifa, Israel.

    • Tamar L Ben-Shaanan,
    • Hilla Azulay-Debby,
    • Ben Korin,
    • Maya Schiller,
    • Nathaniel L Green &
    • Asya Rolls
  3. Pediatric Pulmonary Unit, Rambam Health Care Campus, Haifa, Israel.

    • Fahed Hakim
  4. Faculty of Biology, Technion–Israel Institute of Technology, Haifa, Israel.

    • Shai S Shen-Orr

Contributions

T.L.B.-S. designed and carried out all of the experiments, interpreted the results and wrote the manuscript; H.A.-D. contributed to the experimental design, carried out experiments, contributed to data analysis and to the manuscript; T.D. and E.S. designed, performed and analyzed the CyTOF experiments and contributed to the manuscript; B.K. and M.S. contributed to the experimental design and execution of the experiments, contributed to analysis of the results and contributed to the manuscript; N.L.G. contributed to the interpretation of the results and the writing the manuscript; Y.A. contributed to the CyTOF data analysis; F.H. contributed to the experimental design and data interpretation; S.S.S.-O. designed and analyzed the CyTOF experiments, contributed with the interpretation of results and wrote the manuscript; and A.R. conceived the project, contributed to the experimental design and the interpretation of results, and wrote the manuscript.

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The authors declare no competing financial interests.

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