T.P.P. van den Bosch

Characterization of ectopic lymphoid structures in different types of acute renal allograft rejection: Ectopic lymphoid structures in renal allografts

We hypothesize that T cells such as interleukin (IL)‐21+B cell lymphoma 6 (BCL6)+ T follicular helper cells can regulate B cell‐mediated immunity within the allograft during acute T cell‐mediated rejection; this process may feed chronic allograft rejection in the long term. To investigate this mechanism, we determined the presence and activation status of organized T and B cells in so‐called ectopic lymphoid structures (ELSs) in different types of acute renal allograft rejection. Biopsies showing the following primary diagnosis were included: acute/active antibody‐mediated rejection, C4d+ (a/aABMR), acute T cell‐mediated rejection grade I (aTCMRI) and acute T cell‐mediated rejection grade II (aTCMRII). Paraffin sections were stained for T cells (CD3 and CD4), B cells (CD20), follicular dendritic cells (FDCs, CD23), activated B cells (CD79A), immunoglobulin (Ig)D, cell proliferation (Ki67) and double immunofluorescent stainings for IL‐21 and BCL6 were performed. Infiltrates of T cells were detected in all biopsies. In aTCMRI, B cells formed aggregates surrounded by T cells. In these aggregates, FDCs, IgD and Ki67 were detected, suggesting the presence of ELSs. In contrast, a/aABMR and aTCMRII showed diffuse infiltrates of T and B cells but no FDCs and IgD. IL‐21 was present in all biopsies. However, co‐localization with BCL6 was observed mainly in aTCMRI biopsies. In conclusion, ELSs with an activated phenotype are found predominantly in aTCMRI where T cells co‐localize with B cells. These findings suggest a direct pathway of B cell alloactivation at the graft site during T cell mediated rejection.

Human renal tubular epithelial cells suppress alloreactive T cell proliferation

Renal tubular epithelial cells (TECs) are one of the main targets of alloreactive T cells during acute rejection. We hypothesize that TECs modulate the outcome of alloimmunity by executing immunosuppressive effects in order to dampen the local inflammation. We studied whether TECs possess immunosuppressive capacities and if indoleamine 2,3‐dioxygenase (IDO) might play a role in suppressing T cell alloreactivity. Next, we studied the role of programmed death ligand 1 (PD‐L1) and intercellular adhesion molecule‐1 (ICAM‐1 with regard to TEC‐related immunomodulatory effects. CD3/CD28 and alloactivated peripheral blood mononuclear cells were co‐cultured with activated TECs. We analysed CD4+ and CD8+ T cell proliferation and apoptosis in the absence or presence of IDO inhibitor 1‐methyl‐L‐tryptophan (1‐L‐MT), anti‐PD‐L1 and anti‐ICAM‐1. Further, we examined whether inhibition of T cell proliferation was cell–cell contact‐dependent. We found that TECs dose‐dependently inhibited CD4+ and CD8+ T cell proliferation (Pu2009<u20090·05). Activated TECs showed significantly increased IDO activity and up‐regulated PD‐L1 and ICAM‐1 expression. Suppressed CD4+ and CD8+ T cell proliferation was only partially restored or failed to restore using 1‐L‐MT. Activated TECs increased early and late apoptosis of proliferating CD4+ and CD8+ T cells; only CD4+ T cell apoptosis was statistically affected by 1‐L‐MT. Transwell experiments revealed that TEC‐mediated immunosuppression is cell–cell contact‐dependent. We found that anti‐ICAM‐1 affected only CD4+ T cell apoptosis and not T cell proliferation. Our data show that TECs suppress both CD4+ and CD8+ T cell proliferation contact dependently. Interestingly, inhibition of proliferation and enhancement of apoptosis of T cell subsets is differentially regulated by indoleamine 2,3‐dioxygenase and ICAM‐1, with no evidence for the involvement of PD‐L1 in our system.

Pretransplant Numbers of CD16+ Monocytes as a Novel Biomarker to Predict Acute Rejection After Kidney Transplantation: A Pilot Study

Acute rejection is one of the major immunological determinants of kidney graft function and survival. Early biomarkers to predict rejection are lacking. Emerging evidence reveals a crucial role for the monocyte/macrophage lineage cells in the pathogenesis of rejection. We hypothesized that higher pretransplant numbers of proinflammatory CD16+ monocytes can predict rejection. The study cohort consisted of 104 kidney transplant recipients (58 with no rejection and 46 with biopsy‐proven rejection) and 33 healthy persons. Posttransplant median follow‐up time was 14.7 mo (interquartile range 0.3–34 mo). Pretransplantation blood samples were analyzed by flow cytometry for monocyte immunophenotypes. Groups were compared by Cox regression models for the occurrence of acute rejection. We documented a significantly increased absolute number of pretransplant CD16+ monocytes in patients who developed biopsy‐proven rejection after transplantation compared with those with no rejection (hazard ratio [HR] 1.60, 95% CI 1.28–2.00, p < 0.001) and healthy persons (HR 1.47, 95% CI 1.18–1.82, p < 0.001). In parallel, significantly fewer absolute numbers of CD16− monocytes were observed at pretransplant time points in rejectors versus nonrejectors (HR 0.74, 95% CI 0.58–0.94, p < 0,014). A higher pretransplant number of CD16+ monocytes is significantly associated with a higher risk of acute rejection after kidney transplantation.