Rejection, regardless of the type and time, significantly worsens the graft function and survival. Emerging evidence has revealed a crucial role for the cells of monocyte-macrophage lineage in the pathogenesis of rejection. Here, we studied monocyte-macrophage compartmental infiltration of 62 kidney transplant biopsies with the diagnosis of 1) acute antibody mediated rejection (aABMR, n = 9), 2) chronic antibody mediated rejection (cABMR, n = 13), 3) acute cellular rejection type I (ACR I, n = 11), 4) acute cellular rejection type II (ACRII, n = 13), and 5) and 15 protocol biopsies from kidney transplants with stable function as controls. Next we studied the relationship between these findings and allograft function and survival in the long term.
Immunohistochemical and immunofluorescent stainings were applied to study monocyte-macrophage infiltration. The intensity of infiltration was quantified by ImageJ analysis and laser scan confocal microscopy. Infiltrating monocytes were characterized by double staining with CD14 and CD16. Infiltrating macrophages were identified by expression of CD68, CD80, CD163 as follows: CD68 + CD80 (M1 type) and CD68 + CD163 (M2 type). Histopathological data was analyzed and correlated to eGFR, creatinine and proteinuria levels at the time of biopsy, 3, 6 and 12 months post-rejection.
Overall, the presence of CD68 + macrophages in kidney biopsies was significantly associated with rejection compared to stable patients regardless of histopathological subtype (p = <0,01). Overall, the presence of CD68 + CD163+ macrophages was signigicantly associated with a lower eGFR at the time of biopsy, and at 3, 6 and 12 months after rejection (p < 0,001). Glomerular infiltration by classical and intermediate monocytes and and the presence of non-classical monocytes in the interstitium were significantly associated with rejection regardless of rejection subtype (p = <0,01). cABMR was characterized by glomerular and tubulointerstitial CD68+ macrophage infitration, and glomerular and tubulointerstitial classical and intermediate monocyte distribution as compared to aABMR (p = <0,05). ACRI and ACRII were charactherized by vascular and tubulointerstitial distribuation of CD68+ cells as compared to aABMR rejection type (p = <0,05).
In sharp contrast to T cells, the presence of CD68 + macrophages in a kidney transplant biopsy is significantly associated with rejection regardless of histopathological subtype. There are significant compartmental differences in the distribution of different macrophage and monocyte subtypes between aABMR and cABMR, as well as between ACR I/II and aABMR. These findings could be of interest for the histopathological classifcation of rejection type. Future clarification of the pathogenetical role and the cell specific markers could help detect new rejection biomarkers.