Biological scaffold implants in a murine volumetric muscle loss trauma model cause time dependent CD62L and CD101 upregulation on "regulatory like" eosinophils

Abstract Introduction: Previously, we reported a strong increase in the recruitment of eosinophils at injured muscle when treated with a biologic scaffold implant. As such, we sought to characterize the surface marker expression of these eosinophils to understand their role at the site of injury. Method: Volumetric muscle loss (VML) model was performed on C57BL/6 mice and was subsequently treated with a biologic scaffold (decellularized extracellular matrix). After 7 and 21 days, post-injury, implanted material along with injured tissue was dissected and converted to single cell suspension for flow cytometry. Results: Compared to uninjured mice, at both 7 and 21 days time point, mice that received biological scaffold featured significantly increased presence of eosinophils at the site of injury. These eosinophils had a ring-shaped nucleus which has been previously associated with regulatory eosinophils. Eosinophils at the site of injury showed time dependent upregulation of CD101 (Mean fold change from uninjured muscle after 7 days post implant was 2.73 and the same was 9.90 after 21 days, (p<0.0001)), and CD62L (Mean fold change from uninjured muscle after 7 days post implant was 3.65 and the same was 11.64 after 21 days(p<0.0001)) expression. Interestingly, the same pattern was not observed with blood eosinophils except that the blood eosinophils at 3-week timepoint were featuring a significant increase in CD62L expression compared with 1 week time point, suggesting potential return of homeostasis in circulatory compartment. Conclusion: Here, we describe time-dependent transformation in eosinophil phenotype in response to biologic scaffold implantation, including upregulation of adhesion molecule CD62L and a regulatory marker CD101.