Deletion of M33 Chemokine Receptor Leads to Decreased Levels of Chronic Rejection in a Murine Tracheal Transplant Model

Objectives: Chronic rejection is a major limiting factor for long-term survival after lung transplantation. Infection with cytomegalovirus (CMV) is considered an independent risk factor for the formation of bronchiolitis obliterans syndrome (BOS). Previous studies have shown that the M33 chemokine receptor is essential for the successful establishment of latency of murine CMV in the salivary glands. The aim of this study was to analyze viral effector mechanisms and to investigate the impact of the M33 receptor on airway graft rejection in a mouse transplant model using a M33 deleted virus strain.

Methods: MHC class I-mismatched tracheas of C.B10-2b/LilMcdJ donor mice were transplanted into BALB/c recipients. Transplanted mice were infected at different infection dates reflecting the different clinical settings of viral recipient (R)-donor (D)-serostatus: 7d pre-OP (D-/R+), 7d post-OP (D+/R-), and 7d pre- and post-OP (D+/R+). Furthermore, we matched two different viral strains: wild-type (WT) and a M33-deleted (delM33) MCMV. In vivo imaging was conducted to ensure viral replication. Grafts were harvested on days 21 and 37 after transplantation for histological, morphometric, and immunofluorescence analysis. Intragraft cytokine mRNA production was analyzed by qRT-PCR.

Results: Histological analysis showed significantly increased rejection in WT-infected mice compared with uninfected allografts in all infection groups, reflected in a lower epithelium lamina propria ratio (ELR) (ELR 0.48 ± 0.09 [WT⁺ 7 post] vs. ELR 0.70 ± 0.09 [allo ninf]; p < 0.05). Furthermore, we observed significantly less rejection in the delM33-infected groups compared to WT-infected groups (ELR 0.48 ± 0.09 [WT⁺ 7 post] vs. 0.67 ± 0.04 [delM33⁺ 7 post] ; p < 0.05). When analyzing the different infection regimen, we observed decreased rejection in all preinfected compared with postinfected groups (i.e., 0.48 ± 0.09 [WT⁺ 7 post] vs. 0.56 ± 0.08 [WT⁺ 7 pre] ; p < 0.05). Analysis of cellular infiltration revealed significantly more CD8⁺ T-cells in WT⁺ 7 d post-OP group compared with uninfected allografts.

Conclusion: These data suggest that MCMV infection plays an important role in the development of bronchiolitis obliterans, especially for acute CMV infections after transplantation. Deletion of chemokine receptor M33 leads to decreased levels of rejection. The D- R-serostatus has an impact on the extent of graft rejection in this mouse transplant model.

No conflict of interest has been declared by the author(s).