Camillo Carrara

Significance Statement Renal macrophages are key cells in controlling processes related to inflammation or repair after ischemia-reperfusion injury. Although macrophages from a donor kidney could also guide adaptive immune responses against renal tissue by virtue of their ability to act as antigen-presenting cells, data are lacking on whether donor-derived renal macrophages can function in this manner after being subjected to transplant-induced ischemia-reperfusion injury. The authors demonstrate in mice that such injury is sufficient to dampen donor renal macrophages’ ability to present antigens, skewing them toward a proreparative phenotype. Donor renal macrophages lacking IL-1R8 failed to orchestrate tissue repair, indicating that IL-1R8 is a key regulator of this shift. IL-1R8 thus represents a pathway that merits exploration in terms of modulating responses against autoantigens and alloantigens after kidney transplant. Background In donor kidneys subjected to ischemia-reperfusion injury during kidney transplant, phagocytes coexpressing the F4/80 and CD11c molecules mediate proinflammatory responses and trigger adaptive immunity in transplantation through antigen presentation. After injury, however, resident renal macrophages coexpressing these surface markers acquire a proreparative phenotype, which is pivotal in controlling inflammation and fibrosis. No data are currently available regarding the effects of transplant-induced ischemia-reperfusion injury on the ability of donor-derived resident renal macrophages to act as professional antigen-presenting cells. Methods We evaluated the phenotype and function of intragraft CD11c + F4/80 + renal macrophages after cold ischemia. We also assessed the modifications of donor renal macrophages after reversible ischemia-reperfusion injury in a mouse model of congeneic renal transplantation. To investigate the role played by IL-1R8, we conducted in vitro and in vivo studies comparing cells and grafts from wild-type and IL-R8–deficient donors. Results Cold ischemia and reversible ischemia-reperfusion injury dampened antigen presentation by renal macrophages, skewed their polarization toward the M 2 phenotype, and increased surface expression of IL-1R8, diminishing activation mediated by toll-like receptor 4. Ischemic IL-1R8–deficient donor renal macrophages acquired an M 1 phenotype, effectively induced IFN γ and IL-17 responses, and failed to orchestrate tissue repair, resulting in severe graft fibrosis and aberrant humoral immune responses. Conclusions IL-1R8 is a key regulator of donor renal macrophage functions after ischemia-reperfusion injury, crucial to guiding the phenotype and antigen-presenting role of these cells. It may therefore represent an intriguing pathway to explore with respect to modulating responses against autoantigens and alloantigens after kidney transplant.

Diabetic nephropathy (DN), the single strongest predictor of mortality in patients with type 2 diabetes, is characterized by initial glomerular hyperfiltration with subsequent progressive renal function loss with or without albuminuria, greatly accelerated with the onset of overt proteinuria. Experimental and clinical studies have convincingly shown that early interventions retard disease progression, while treatment if started late in the disease course seldom modifies the slope of GFR decline. Here we assessed whether the negligible renoprotection afforded by drugs in patients with proteinuric DN could be due to loss of glomerular structural integrity, explored by scanning electron microscopy (SEM). In diabetic patients with early renal disease, glomerular structural integrity was largely preserved. At variance SEM documented that in the late stage of proteinuric DN, glomerular structure was subverted with nearly complete loss of podocytes and lobular transformation of the glomerular basement membrane. In these circumstances one can reasonably imply that any form of treatment, albeit personalized, is unlikely to reach a given cellular or molecular target. These findings should persuade physicians to start the putative renoprotective therapy soon after the diagnosis of diabetes or in an early phase of the disease before structural integrity of the glomerular filter is irreversibly compromised.

BACKGROUND: Complement activation contributes to lung dysfunction in coronavirus disease 2019 (COVID-19). We assessed whether C5 blockade with eculizumab could improve disease outcome. METHODS: In this single-centre, academic, unblinded study two 900 mg eculizumab doses were added-on standard therapy in ten COVID-19 patients admitted from February 2020 to April 2020 and receiving Continuous-Positive-Airway-Pressure (CPAP) ventilator support from ≤24 hours. We compared their outcomes with those of 65 contemporary similar controls. Primary outcome was respiratory rate at one week of ventilator support. Secondary outcomes included the combined endpoint of mortality and discharge with chronic complications. RESULTS: Baseline characteristics of eculizumab-treated patients and controls were similar. At baseline, sC5b-9 levels, ex vivo C5b-9 and thrombi deposition were increased. Ex vivo tests normalised in eculizumab-treated patients, but not in controls. In eculizumab-treated patients respiratory rate decreased from 26.8±7.3 breaths/min at baseline to 20.3±3.8 and 18.0±4.8 breaths/min at one and two weeks, respectively (p<0.05 for both), but did not change in controls. Between-group changes differed significantly at both time-points (p<0.01). Changes in respiratory rate correlated with concomitant changes in ex vivo C5b-9 deposits at one (rs = 0.706, p = 0.010) and two (rs = 0.751, p = 0.032) weeks. Over a median (IQR) period of 47.0 (14.0-121.0) days, four eculizumab-treated patients died or had chronic complications versus 52 controls [HRCrude (95% CI): 0.26 (0.09-0.72), p = 0.010]. Between-group difference was significant even after adjustment for age, sex and baseline serum creatinine [HRAdjusted (95% CI): 0.30 (0.10-0.84), p = 0.023]. Six patients and 13 controls were discharged without complications [HRCrude (95% CI): 2.88 (1.08-7.70), p = 0.035]. Eculizumab was tolerated well. The main study limitations were the relatively small sample size and the non-randomised design. CONCLUSIONS: In patients with severe COVID-19, eculizumab safely improved respiratory dysfunction and decreased the combined endpoint of mortality and discharge with chronic complications. Findings need confirmation in randomised controlled trials.