Chemokine decoy receptor D6 mimicking trap (D6MT) prevents allosensitization and immune rejection in murine corneal allograft model

Single-Cell RNA sequencing highlights the regulatory role of T cell marker genes Ctla4, Ccl5 and Tcf7 in corneal allograft rejection of mouse model

BACKGROUND

A mouse corneal allograft model was induced and single-cell RNA sequencing (scRNA-seq) data of corneal tissues and T cells were analyzed to reveal a T cell-mediated mechanism for corneal allograft rejection in mice.

METHODS

Corneal tissue samples from a mouse model of corneal allograft were collected for scRNA-seq analysis, followed by quality control, dimensionality reduction, cluster analysis and enrichment analysis. A large number of highly variable genes were identified in mice with corneal allograft. Significant difference existed in immune T cells, especially in CD4 + T cells.

RESULTS

It was found that T cell marker genes Ctla4, Ccl5, Tcf7, Lgals1, and Itgb1 may play key roles in the corneal allograft rejection. Mice with allograft rejection showed a significant increase in the proportion of CD4 + T cells in the corneal tissues. Besides, Ccl5 and Tcf7 expression was increased in mice with allograft rejection and positively linked to the proportion of CD4 + T cells. Whereas, Ctla4 expression was downregulated and negatively associated with the proportion of CD4 + T cells.

CONCLUSION

Collectively, Ctla4, Ccl5 and Tcf7 may participate in the rejection of corneal allograft in mice by affecting CD4 + T cell activation.

The atypical chemokine receptor-2 fine-tunes the immune response in herpes stromal keratitis

Herpes stromal keratitis (HSK) is a blinding corneal disease caused by herpes simplex virus-1 (HSV-1), a common pathogen infecting most of the world's population. Inflammation in HSK is chemokine-dependent, particularly CXCL10 and less so the CC chemokines. The atypical chemokine receptor-2 (ACKR2) is a decoy receptor predominantly for pro-inflammatory CC chemokines, which regulates the inflammatory response by scavenging inflammatory chemokines thereby modulating leukocyte infiltration. Deletion of ACKR2 exacerbates and delays the resolution of the inflammatory response in most models. ACKR2 also regulates lymphangiogenesis and mammary duct development through the recruitment of tissue-remodeling macrophages. Here, we demonstrate a dose-dependent upregulation of ACKR2 during corneal HSV-1 infection. At an HSV inoculum dose of 5.4 x 105 pfu, but not at higher dose, ACKR2 deficient mice showed prolonged clinical signs of HSK, increased infiltration of leukocytes and persistent corneal neovascularization. Viral clearance and T cell activation were similar in ACKR2-/- and wild type mice, despite a transient diminished expression of CD40 and CD86 in dendritic cells. The data suggest that ACKR2 fine-tunes the inflammatory response and the level of neovascularization in the HSK.

Effects of Hypoxic Preconditioning and Vascular Endothelial Growth Factor on the Survival of Isolated Primary Retinal Ganglion Cells

This study aimed to investigate the effect of hypoxic preconditioning (HPC) on primary retinal ganglion cell (RGC) survival and the associated mechanism, including the role of vascular endothelial growth factor (VEGF). Retinas were separated from the enucleated eyeballs of Sprague-Dawley rats on postnatal days 1-4. RGCs were harvested using an immunopanning-magnetic separation system and maintained for 24 h in a defined medium. Hypoxic damage (0.3% O₂) was inflicted on the cells using a CO₂ chamber. Anti-VEGF antibody (bevacizumab) was administered to RGCs exposed to hypoxic conditions, and RGC survival rate was compared to that of non-anti-VEGF antibody-treated RGCs. HPC lasting 4 h significantly increased RGC survival rate. In the RGCs exposed to hypoxic conditions for 4 h, VEGF mRNA and protein levels were significantly increased. Treatment with high dose bevacizumab (>1 mg/mL) countered HPC-mediated RGC survival. Protein kinase B and focal adhesion kinase levels were significantly increased in 4-h hypoxia-treated RGCs. HPC showed beneficial effects on primary RGC survival. However, only specifically controlled exposure to hypoxic conditions rendered neuroprotective effects. Strong inhibition of VEGF inhibited HPC-mediated RGC survival. These results indicate that VEGF may play an essential role in promoting cell survival under hypoxic conditions.

The atypical chemokine receptor-2 does not alter corneal graft survival but regulates early stage of corneal graft-induced lymphangiogenesis

Purpose

To re-evaluate the role of the atypical chemokine receptor-2 (ACKR2) in corneal graft rejection and investigate the effect of ACKR2 on inflammation-associated lymphangiogenesis using murine orthotopic corneal transplantation.

Methods

Corneal grafts were performed and evaluated in the settings of syngeneic, allogeneic and single antigen (HY-antigen) disparity pairings. Corneal vessels were quantified in whole mounts from WT, ACKR2^−/− and F4/80^−/−ACKR2^−/− mice that received syngeneic or allogeneic grafts using anti-CD31 and anti-Lyve-1 antibodies.

Results

Syngeneic corneal grafts in WT and ACKR2^−/− mice were 100% accepted. Fully histo-incompatible allogeneic grafts were rapidly rejected (100%) with similar tempo in both WT and ACKR2^−/− hosts. Around 50% of single-antigen (HY) disparity grafts rejected at a slow but similar tempo (60 days) in WT and ACKR2^−/− mice. Prior to grafting, F4/80^−/−ACKR2^−/− mice had lower baseline levels of limbal blood and lymphatic vessels compared to ACKR2^−/− mice. Syngeneic grafts, but not allogeneic grafts, in ACKR2^−/− and F4/80^−/−ACKR2^−/− mice induced higher levels of lymphatic sprouting and infiltration of Lyve-1⁺ cells during the early (3d) post-graft (pg) stage but lymphatic density was similar to WT grafted mice by 7d pg.

Conclusions

Our results indicate that the chemokine scavenger receptor, ACKR2, has no role to play in the survival of allogeneic grafts. A minor role in regulation of lymphangiogenesis in the early stage of wound healing in syngeneic grafts is suggested, but this effect is probably masked by the more pronounced lymphangiogenic inflammatory response in allogeneic grafts. No additional effect was observed with the deletion of the resident macrophage gene, F4/80.

Gr-1intCD11b+ myeloid-derived suppressor cells accumulate in corneal allograft and improve corneal allograft survival

We identified the characteristics of myeloid-derived suppressor cells (MDSCs) and investigated their mechanism of induction and their functional role in allograft rejection using a murine corneal allograft model. In mice, MDSCs coexpress CD11b and myeloid differentiation antigen Gr-1. Gr-1⁺CD11b⁺ cells infiltrated allografted corneas between 4 d and 4 wk after surgery; however, the frequencies of Gr-1⁺CD11b⁺ cells were not different between accepted and rejected allografts or in peripheral blood or BM. Of interest, Gr-1^intCD11b⁺ cells, but not Gr-1^hiCD11b⁺ cells, infiltrated the accepted graft early after surgery and expressed high levels of immunosuppressive cytokines, including IL-10, TGF-β, and TNF-related apoptosis-inducing ligand. This population remained until 4 wk after surgery. In vitro, only high dose (>100 ng/ml) of IFN-γ plus GM-CSF could induce immunosuppressive cytokine expression in Gr-1^intCD11b⁺ cells. Furthermore, adoptive transfer of Gr-1^intCD11b⁺ cells reduced T cell infiltration, which improved graft survival. In conclusion, high-dose IFN-γ in allograft areas is essential for development of Gr-1^intCD11b⁺ MDSCs in corneal allografts, and subtle environmental changes in the early period of the allograft can result in a large difference in graft survival.

Overview and potential unifying themes of the atypical chemokine receptor family

Chemokines modulate immune responses through their ability to orchestrate the migration of target cells. Chemokines directly induce cell migration through a distinct set of 7 transmembrane domain G protein-coupled receptors but are also recognized by a small subfamily of atypical chemokine receptors, characterized by their inability to support chemotactic activity. Atypical chemokine receptors are now emerging as crucial regulatory components of chemokine networks in a wide range of physiologic and pathologic contexts. Although a new nomenclature has been approved recently to reflect their functional distinction from their conventional counterparts, a systematic view of this subfamily is still missing. This review discusses their biochemical and immunologic properties to identify potential unifying themes in this emerging family.