Although induction of CD8 T-cell responses to transplants requires CD4-cell help, how this help is transmitted remains incompletely characterized. In vitro, cognate interactions between CD4 T cells and dendritic cells (DCs) induceC3a and C5a production. CD8 ؉ T cells lacking C3a receptor (C3aR) and C5a receptor (C5aR) proliferate weakly to allogeneic DCs despite CD4 help, indicating that CD4-cell help is mediated, in part, through DC-derived C3a/C5a acting on CD8 ؉ T cellexpressed C3aR/C5aR. In support of this concept, aug-

While activation of serum complement mediates antibody-initiated vascular allograft injury, increasing evidence indicates that complement also functions as a modulator of alloreactive T cells. We tested whether blockade of complement activation at the C5 convertase step affects T cell-mediated cardiac allograft rejection in mice. The anti-C5 mAb BB5.1, which prevents the formation of C5a and C5b, synergized with sub-therapeutic doses of CTLA4Ig to significantly prolong the survival of C57BL/6 heart grafts that were transplanted into naive Balb/c recipients. Anti-C5 mAb treatment limited the induction of donor-specific IFNγ-producing T cell alloimmunity without inducing Th2 or Th17 immunity in vivo and inhibited primed T cells from responding to donor antigens in secondary mixed lymphocyte responses. Additional administration of anti-C5 mAb to the donor prior to graft harvest further prolonged graft survival and concomitantly reduced both the in vivo trafficking of primed T cells into the transplanted allograft and decreased expression of T cell chemoattractant chemokines within the graft. Together these results support the novel concept that C5 blockade can inhibit T cell-mediated allograft rejection through multiple mechanisms, and suggest that C5 blockade may constitute a viable strategy to prevent and/or treat T cell-mediated allograft rejection in humans.

Complement activation is integral to the development and progression of multiple forms of kidney disease. The liver is the principal source of serum complement, but various kidney cell types and bone marrow-derived immune cells can produce a full array of complement proteins. Locally produced and activated complement yields cleavage products that function as vital intermediaries, amplifying inflammation in ischemia-reperfusion injury and transplant rejection, among other pathological states. Additional new studies indicate that during cognate T-cell-antigen presenting cell interactions, both cell types produce alternative pathway complement components. The resultant activation products have an essential role in T-cell activation, expansion, and differentiation, which in turn has a profound impact on the development of immune-mediated kidney disease. The recognition of an expanded role for kidney cell-derived and immune cell-produced complement as pathogenic to the kidney supports the need for future studies to test the efficacy of complement inhibitors in the prevention and/or treatment of selected kidney diseases.

Transcription factor NF-κB regulates expression of numerous genes that control inflammation and is activated in glomerular cells in glomerulonephritis (GN). We previously identified genetic variants for a NF-κB regulatory, ubiquitin-binding protein ABIN1 as risk factors for GN in systemic autoimmunity. The goal was to define glomerular inflammatory events controlled by ABIN1 function in GN. Nephrotoxic serum nephritis was induced in wild-type (WT) and ubiquitin-binding deficient ABIN1[D485N] mice, and renal pathophysiology and glomerular inflammatory phenotypes were assessed. Proteinuria was also measured in ABIN1[D485N] mice transplanted with WT mouse bone marrow. Inflammatory activation of ABIN1[D472N] (D485N homolog) cultured human-derived podocytes, and interaction with primary human neutrophils were also assessed. Disruption of ABIN1 function exacerbated proteinuria, podocyte injury, glomerular NF-κB activity, glomerular expression of inflammatory mediators, and glomerular recruitment and retention of neutrophils in antibody-mediated nephritis. Transplantation of WT bone marrow did not prevent the increased proteinuria in ABIN1[D845N] mice. Tumor necrosis factor-stimulated enhanced expression and secretion of NF-κB-targeted proinflammatory mediators in ABIN1[D472N] cultured podocytes compared with WT cells. Supernatants from ABIN1[D472N] podocytes accelerated chemotaxis of human neutrophils, and ABIN1[D472N] podocytes displayed a greater susceptibility to injurious morphologic findings induced by neutrophil granule contents. These studies define a novel role for ABIN1 dysfunction and NF-κB in mediating GN through proinflammatory activation of podocytes.

Uterine NK cells (uNK) are a distinct immune population which influence pregnancy outcome. While murine studies have suggested that tissue-resident uNKs predominate in virgin endometrium, the origin of uNKs in humans is unknown. To define subsets of uterine NKs in humans and determine their developmental origin, we performed single-cell RNA-sequencing on CD56+ uNKs sorted from endometrial biopsies of 4 healthy controls (HCs) (17,146 cells) and 5 uterus transplant (UTx) recipients (30,351 cells). SNP polymorphisms and HLA alleles were used to identify cells of donor (tissue-resident) or recipient (peripheral) origin in UTx recipients. Developmental trajectories were built with Monocle v.3.0. Ten major clusters were identified in HCs, with 48% of endometrial NK cells (eNKs) occupying 3 clusters (eNK1–3) that shared gene signatures with known human decidual NK cell subsets (dNK1–3). Pseudotime analysis revealed that the eNK1–3 clusters arose from proliferating subsets and were less mature than cytotoxic uNKs expressing ZEB2, TBX21, and FCGR3A (CD16). uNKs from UTx recipients were similarly distributed across the clusters, with a trend towards fewer cells in the FCGR3A-expressing mature subset. Notably, recipient-derived uNKs dominated all uNK subsets within four months post-transplant but became less frequent in UTx recipients >1 year after transplant (95% vs. 72%; early vs. late). The proportion of donor-derived to recipient-derived cells remained constant across subsets in all UTx recipients. In contrast to mouse models, our study suggests that human uNKs derive primarily from blood-borne peripheral immigrants and that environmental factors influence uNK differentiation more than genotype or developmental origin.