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Abstract
The role of negative regulators or suppressors of the damage-associated molecular pattern–mediated (DAMP-mediated) stimulation of innate immune responses is being increasingly appreciated. However, the presence and function of suppressors of DAMP-mediated effects on T cells, and whether they can be targeted to mitigate T cell–dependent immunopathology remain unknown. Sialic acid–binding immunoglobulin-like lectin G (Siglec-G) is a negative regulator of DAMP-mediated responses in innate immune cells, but its T cell–autonomous role is unknown. Utilizing loss-of-function–based (genetic knockout) and gain-of-function–based (agonist) approaches, we demonstrate that in the presence of certain DAMPs, Siglec-G suppressed in vitro and in vivo T cell responses. We also demonstrate that its T cell–autonomous role is critical for modulating the severity of the T cell–mediated immunopathology, graft-versus-host disease (GVHD). Enhancing the Siglec-G signaling in donor T cells with its agonist, a CD24Fc fusion protein, ameliorated GVHD while preserving sufficient graft-versus-tumor (GVT) effects in vivo. Collectively, these data demonstrate that Siglec-G is a potentially novel negative regulator of T cell responses, which can be targeted to mitigate GVHD.
Authors
Tomomi Toubai, Corinne Rossi, Katherine Oravecz-Wilson, Cynthia Zajac, Chen Liu, Thomas Braun, Hideaki Fujiwara, Julia Wu, Yaping Sun, Stuart Brabbs, Hiroya Tamaki, John Magenau, Pang Zheng, Yang Liu, Pavan Reddy
Murine T cells do not express Siglec-G on the surface
Submitter: Lars Nitschke | lars.nitschke@fau.de
Authors: Lars Nitschke, Carolin Brandl, Matthew S. Macauley, and James C. Paulson
University of Erlangen
Published December 18, 2017
Toubai et al. describe a T-cell autonomous role of Siglec-G in suppressing T-cell responses in presence of a damage-associated molecular pattern (DAMP) protein and they report an apparent expression of Siglec-G on the T cell surface. This is in contrast to studies by our two groups with two newly generated monoclonal antibodies (mAb) against Siglec-G, the mAbs, SH2.1 (1) and another mAb against Siglec-G (2), where we did not see any Siglec-G expression on the T cell surface. Toubai et al. show in Fig. 1B a mean-fluorescence intensity (MFI) shift of the whole T-cell population stained with our SH2.1 mAb, in comparison to an isotype control, suggesting a low Siglec-G expression on T cells. In Suppl. Fig.1 no MFI difference is found between the main T-cell population of WT and Siglec-G KO mice, but a subpopulation of 3-5% of WT T-cells is positive for Siglec-G.
We think that comparison of WT and KO T-cells is crucial, as isotype controls can be misleading due to different fluorophore numbers per antibody, other purity or other concentration than the specific antibody. We have performed new experiments independently in two labs examining Siglec-G expression on T-cells with our two different mAbs, using two different strains of Siglec-G KO mice as controls (3,4). Our experiments do not show any evidence for Siglec-G expression on the surface of T-cells. Neither SH2.1 used by the Nitschke group (1), the same antibody as was used by Toubai et al., nor the other anti-Siglec-G mAb , used by the Macauley/Paulson group did stain any T cells, while B cells were clearly positive for Siglec-G. We think the findings of study by Toubai et al.. of hyperactivated T cells in Siglec-G deficient mice could be explained by the loss of Siglec-G on DCs and B cells affecting T cells indirectly. In conclusion, we see no indication for Siglec-G expression on the surface of mouse T-cells.
References
1. Hutzler, et al. J Immunol. 2014; 192: 5406
2. Pfrengle, F., et al. J Immunol 2013; 191: 1724
3. Hoffmann,et al. Nat Immunol 2007; 8: 695
4. Ding, et al. PLoS ONE 2007;2: e997.
