*Purpose: Blood monocytes differentiating into tissue macrophages or dendritic cells are involved in multiple immune responses including reactions to the transplanted allograft. Peripheral monocytes can be further categorized into specific subpopulations according to the expression level of CD14 and CD16 antigens. In addition to prevailing “classical“(CD14⁺CD16^–) monocytes, there are also “intermediate” (CD14⁺CD16⁺) and “non-classical” (CD14^lowCD16⁺) monocytes with exaggerated inflammatory responses. Tissue macrophages may be divided into pro-inflammatory M1 type and anti-inflammatory population M2 expressing CD163 and CD206. The aim of our study was to characterize the expression of M2-related molecules in different subsets of monocytes and in relationship to occurrence of acute rejection. Simultaneously, additional myeloid functional antigens such as CD47 and HLA-DR were evaluated.

*Methods: In total 202 patients who underwent renal transplantation from deceased donor were enrolled in the prospective study. All patients gave their informed consent according to a protocol approved by the Ethics Committee. Peripheral blood samples were collected before kidney transplantation and day 7, 1 month, 3 months, and 1 year post-transplantation. Blood monocytes were evaluated for the expresssion of CD14, CD16, CD163, CD47 and HLA-DR by flow cytometry.

*Results: The expression of CD163 was markedly induced during the first week after transplantation in all three subpopulations of peripheral monocytes with higher pre-transplant levels in patients developing acute rejection. CD206, as an alternative M2 marker expressed only on a limited number of blood monocytes, was upregulated after the transplantation in acute rejection group but its expression at one month after the transplantation was lower in these subjects. Serum levels of IL-10, an anti-inflammatory cytokine characteristic for M2 macrophages, were elevated after the transplantation and did not correlate with the expression of either CD163 or CD206 on blood monocytes. The expression of CD47 decreased after the transplantation while the number of HLA-DR-negative monocytes, recently associated with myeloid-derived suppressor cells, was up-regulated.

*Conclusions: We assume from our data that peripheral blood monocytes can change their phenotypic pattern after the kidney allograft transplantation and combination of several membrane markers might be helpful in assessing potential risk of acute rejection.

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