Persisting Donor Alveolar Macrophages Have Increased Expression of Scavenger Receptor CD206 Compared to Graft-Infiltrating Recipient-Derived Macrophages Following Lung Transplantation

Purpose

Alveolar macrophages play vital roles in attenuating lung injury through immune modulatory effects and improving gas exchange by scavenging cellular debris within the alveoli. A recent analysis of lung biopsy specimens suggests that donor-derived macrophages persist within the allograft after lung transplantation. The phenotypic differences between donor and graft-infiltrating recipient macrophages remains unreported.

Methods

Single cell suspensions obtained from bronchoalveolar lavage (BAL) of 15 lung transplant recipients at various times following transplantation were analyzed by flow cytometry. Macrophages were defined as CD45+CD3-CD19-CD64+CD14+CD11c^hisinglets. Cell origin (donor versus recipient) was identified by staining for human leukocyte antigen discrepancies. Paired t test was used to compare cell surface marker expression between donor and recipient macrophages.

Results

The proportion of donor macrophages within the BAL was variable across patients but did not vary over the time following transplantation (p = 0.5). The median percentage of donor macrophages was 10.5% (range 1-64). Donor macrophages had increased expression of CD206 (Figure: Rep. flow cytometry plot from BAL one month following transplantation and cumulative data from 10 participants, p = 0.004), with trends in increased expression of HLADR (p = 0.07), and no difference in CD163 expression (p = 0.17).

Conclusion

The scavenger function of alveolar macrophages is vital in maintaining gas exchange in the setting of severe influenza infection. Following lung transplantation, persisting donor-derived alveolar macrophages have significantly increased expression of the scavenger receptor CD206 when compared to graft-infiltrating recipient-derived macrophages. Further investigation is warranted to identify whether this has implications for graft function in the perioperative setting.