Dépôt de bilirubine dans les greffons rénaux lors d'un rejet – BIRD Study

Objectif(s) de la recherche et intérêt pour la santé publique

Finalité de l'étude

Objectifs poursuivis

Domaines médicaux investigués

Bénéfices attendus

Bilirubin, traditionally viewed as a waste product of heme breakdown, is increasingly recognized as a bioactive molecule with systemic signaling roles. It can attenuate oxidative stress, modulate complement activation, and influence leukocyte–endothelial interactions, and epidemiological studies in non-transplant populations have linked higher circulating bilirubin levels with reduced cardiovascular and kidney disease risk. In kidney transplantation, large cohort data have reported inverse associations between post-transplant serum bilirubin and rejection risk, graft loss, and impaired graft function, suggesting that bilirubin may reflect or contribute to mechanisms limiting immune-mediated injury. However, other clinical analyses have not observed statistically significant associations between serum bilirubin and graft outcomes, highlighting the complexity of interpreting systemic bilirubin measures in this context.
Despite these population-level observations, little is known about local bilirubin accumulation within the graft parenchyma and its relationship to alloimmune pathology. A recent mechanistic study in human cardiac allografts with vasculopathy demonstrated that intragraft plasma cells often produce antibodies recognizing bilirubin, that bilirubin deposits are present within immune infiltrates and smooth muscle cells in affected vessels, and that infiltrating macrophages express key heme catabolic enzymes, including HO-1 and biliverdin reductases, alongside evidence of iron deposition. These findings support the concept that local heme catabolism and biliverdin/bilirubin metabolism may be active within rejecting graft tissue and could serve as immunologic targets or modulators of chronic allograft injury.
In kidney allografts, ABMR and TCMR each involve patterns of microvascular damage, complement activation, and immune cell infiltration that could plausibly release heme from damaged cells and local erythrocytes, activate HO-1 pathways, and generate bilirubin in situ. Whether this local bilirubin is simply a byproduct of injury or contributes to immune phenotypes, including DSA-dependent and independent infiltrates, remains unknown. Understanding the presence, localization, and extent of bilirubin deposition in kidney transplant biopsies across different rejection phenotypes, and its relationship with immune cell infiltrates and histologic injury, will clarify whether heme catabolism participates in the pathophysiology of rejection and could reveal novel metabolic or immunologic biomarkers or therapeutic targets.