Research ArticleIMMUNOLOGY

Neuron-specific SALM5 limits inflammation in the CNS via its interaction with HVEM

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Science Advances  08 Apr 2016:
Vol. 2, no. 4, e1500637
DOI: 10.1126/sciadv.1500637
  • Fig. 1 Identifying SALM5 as a gene specifically expressed in the CNS.

    (A) Strategy used to identify molecules with Ig-like domains that are enriched in immune-privileged organs. (B) Expression profile of the SALM family in different human organs or cell types. (C) Staining of lymphocytes (as indicated from normal mice) for SALM5 fusion protein binding by flow cytometry. (D) SALM5 mRNA expression in different mouse tissues determined by reverse transcription polymerase chain reaction (RT-PCR). (E) SALM5 mAb (clone 7A10) staining of human embryonic kidney 293T (HEK293T) cells transfected with mouse SALM5 (mSALM5) full-length (right panel) or control (left panel) plasmid. (F) Expression of SALM5 in normal tissues. Paraffin-embedded naïve mouse tissues (as indicated) were stained using a biotin-labeled SALM5 mAb.

  • Fig. 2 SALM5 mAb treatment enhanced inflammation in the CNS.

    (A) Mice treated with SALM5 mAb or control antibody were intravenously injected with LPS. Twenty-four hours later, mice were sacrificed and their spinal cords were stained to detect the expression of Iba-1. Data are representative of three experiments with three mice in each group. (B) Isolated microglia from naïve B6 mice were stained using biotin-conjugated mSALM-Ig, which was preincubated with control or anti-SALM5 mAb. (C) Peritoneal macrophages were isolated and cultured overnight with irradiated SALM5+ HEK293T cells or control HEK293T cells. LPS was added to the culture at the indicated doses for 8 hours. The culture medium was then harvested and tested for cytokines. Data are representative of two independent experiments. *P < 0.05 (unpaired Student’s t test).

  • Fig. 3 Identification of HVEM as the counter-receptor for SALM5.

    (A) A library of human transmembrane genes was screened using purified recombinant SALM5 fusion protein. Graphic views of individual wells with positive hits for SALM5-Ig are shown. (B) HEK293T cells transfected with mouse HVEM (mHVEM) were stained by mSALM5-Ig in the presence of control mAbs (left panel) or HVEM mAb (right panel). (C) HVEM counter-receptors were screened by CDS. A three-dimensional illustration of the results from one 384-well plate is shown; all positive hits for HVEM-Ig are indicated. (D) Human HVEM (hHVEM) interacted with four counter-receptors. HEK293T cells were transiently transfected to express human genes, as indicated, and were stained with hHVEM-Ig (open histograms) or control Ig (filled histograms). (E) mHVEM interacted with mouse counter-receptors. HEK293T cells were transiently transfected to express mLIGHT, mCD160, or mSALM5, and were stained with mHVEM-Ig (open histograms) or control Ig (filled histograms). (F) Anti-SALM5 mAb (clone 7A10) blocked the SALM5-HVEM interaction. HEK293T cells were transiently transfected with the plasmid encoding mSALM5 (open) or the control plasmid (close). HEK293T transfectants were preincubated with control antibody or anti-SALM5 mAb before being stained with mHVEM-Ig.

  • Fig. 4 Binding sites in the SALM5-HVEM interaction.

    (A) Competitive binding of SALM5 with other HVEM counter-receptors. HEK293T cells transfected with mHVEM were incubated with mBTLA, mCD160, or mLIGHT recombinant fusion proteins before being stained by biotin-labeled mSALM5-Ig. (B) Identification of the interacting domain on HVEM. Full-length HVEM [wild-type (WT)], HVEM without the CRD1 domain, or HVEM mutants with point mutation, as indicated, were individually expressed in HEK293T cells and stained with SALM5-Ig (lower panels). The expression of WT and mutated HVEM was verified by HVEM polyclonal antibody staining (upper panels). (C and D) Identification of the binding domain on SALM5 for HVEM. Each extracellular domain for SALM5, including LRR, Ig, and FN, was swapped with the corresponding domain on SALM3 using PCR cloning and fused to a C-terminal enhanced green fluorescent protein (EGFP). These chimeric mutants were transiently expressed in HEK293T cells and stained using mHVEM-Ig. A summary of the binding assay by flow cytometry (D), positive binding to mHVEM (+), or negative binding to mHVEM (−) was indicated (C).

  • Fig. 5 SALM5 interacts with HVEM to inhibit EAE.

    (A) Aggravation of EAE induced by blocking of the SALM5-HVEM interaction. WT and HVEM-knockout mice (HVEM−/−) were immunized with MOG(35–55) peptide to induce EAE. SALM5 mAb or control antibody was given on days 10, 14, and 17 after MOG immunization (n = 7). Clinical scores of EAE were measured daily. Representative results from three independent experiments are shown. *P < 0.05 (unpaired Student’s t test). (B) Pathology of spinal cord sections from mice on day 19 after EAE induction. Inflammatory infiltrates in spinal cords were revealed using H&E staining. The infiltrates were further visualized by staining with mAb against CD3 for T cells or with mAb against MAC3 for macrophages. (C and D) Quantification of infiltrating mononuclear cells in the CNS. The mouse brains and spinal cords were prepared and extracted on day 19 after EAE induction. Total numbers of mononuclear cells (C), as well as the respective numbers of CD4+ T cells, CD8+ T cells, B cells, macrophages, and microglia (D) in the CNS were counted using flow cytometry. Data are representative of three independent experiments with five mice in each group. *P < 0.05 (unpaired Student’s t test). (E) RT-PCR detection of the proinflammatory cytokine mRNA levels in the spinal cords of naïve mice or mice treated with SALM5 mAb or control antibody after EAE induction. (F) Immunohistochemical staining of activated microglia by Iba-1 expression in the spinal cords of mice with EAE. The folds of amplification in the micrograph are shown on the right. (G) Expression of MHC class II and CD80 in microglia cells isolated from the CNS after EAE induction with SALM5 mAb (open histogram) or control antibody (shaded histogram) treatment. Data are representative of two independent experiments with three mice in each group. (H) Levels of proinflammatory cytokines secreted by microglia/macrophages. The microglia/macrophages were isolated from the CNS of naïve, control antibody, or anti-SALM5 mAb–treated mice 16 days after immunization. Cells were cultured without further stimulation, and the supernatants were harvested after 12 hours. Different cytokine levels were measured using the BD Cytometric Bead Array (CBA) mouse inflammatory cytokine kit. Data are representative of three independent experiments with three mice in each group. *P < 0.05 (unpaired Student’s t test).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/4/e1500637/DC1

    Supplementary Materials and Methods

    Fig. S1. Expression profile of 15 genes enriched in immune-privileged organs.

    Fig. S2. Immunostaining of SALM5 in normal mouse brain sections by different mSALM5 antibodies.

    Fig. S3. Expression of SALM5 protein in mouse tissues.

    Fig. S4. Effect of SALM5 mAb on LPS-induced systemic inflammation.

    Fig. S5. CDS screening of a library of transmembrane proteins.

    Fig. S6. Binding of the mouse BTLA and CD160 binding by mHVEM mutants.

    Fig. S7. Identification of the binding domain on mSALM5 for mSALM mAb.

    Fig. S8. SALM5 did not directly affect T cell proliferation.

    Fig. S9. Administration of F(ab′)2 of SALM5 mAb aggravates EAE.

    Fig. S10. SALM5, but not CD160, inhibits microglia inflammation.

    Fig. S11. HVEM is highly expressed in resting lymphocytes and microglia.

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Materials and Methods
    • Fig. S1. Expression profile of 15 genes enriched in immune-privileged organs.
    • Fig. S2. Immunostaining of SALM5 in normal mouse brain sections by different mSALM5 antibodies.
    • Fig. S3. Expression of SALM5 protein in mouse tissues.
    • Fig. S4. Effect of SALM5 mAb on LPS-induced systemic inflammation.
    • Fig. S5. CDS screening of a library of transmembrane proteins.
    • Fig. S6. Binding of the mouse BTLA and CD160 binding by mHVEM mutants.
    • Fig. S7. Identification of the binding domain on mSALM5 for mSALM mAb.
    • Fig. S8. SALM5 did not directly affect T cell proliferation.
    • Fig. S9. Administration of F(ab′)2 of SALM5 mAb aggravates EAE.
    • Fig. S10. SALM5, but not CD160, inhibits microglia inflammation.
    • Fig. S11. HVEM is highly expressed in resting lymphocytes and microglia.

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