Monocyte-derived dendritic cells (moDCs) dramatically increase in numbers upon infection and inflammation; accordingly, we found that this also occurs during allogeneic responses. Despite their prominence, how emergent moDCs and resident conventional DCs (cDCs) divide their labor as APCs remain undefined. Hence, we compared both direct and indirect presentation by murine moDCs versus cDCs. We found that, despite having equivalent MHC class II expression and in vitro survival, moDCs were 20-fold less efficient than cDCs at inducing CD4+ T cell proliferation through both direct and indirect Ag presentation. Despite this, moDCs were more potent at inducing Th1 and Th17 differentiation (e.g., 8-fold higher IFN-γ and 2-fold higher IL-17A in T cell cocultures), whereas cDCs induced 10-fold higher IL-2 production. Intriguingly, moDCs potently reduced the ability of cDCs to stimulate T cell proliferation in vitro and in vivo, partially through NO production. We surmise that such division of labor between moDCs and cDCs has implications for their respective roles in the immune response.

Plasmacytoid dendritic cells (pDCs) play an important role in immunity to certain pathogens and immunopathology in some autoimmune diseases. They are thought to have a longer lifespan than conventional DCs (cDCs), largely based on a slower rate of BrdU labeling by splenic pDCs. Here we demonstrated that pDC expansion and therefore BrdU labeling by pDCs occurs in bone marrow (BM). The rate of labeling was similar between BM pDCs and spleen cDCs. Therefore, slower BrdU labeling of spleen pDCs likely reflects the “migration time” (∼2 days) for BrdU labeled pDCs to traffic to the spleen, not necessarily reflecting longer life span. Tracking the decay of differentiated DCs showed that splenic pDCs and cDCs decayed at a similar rate. We suggest that spleen pDCs have a shorter in vivo lifespan than estimated utilizing some of the previous approaches. Nevertheless, pDC lifespan varies between mouse strains. pDCs from lupus-prone NZB mice survived longer than C57BL/6 pDCs. We also demonstrated that activation either positively or negatively impacted on the survival of pDCs via different cell-death mechanisms. Thus, pDCs are also short-lived. However, the pDC lifespan is regulated by genetic and environmental factors that may have pathological consequence.

Dendritic cells (DCs) are professional antigen-presenting cells that consist of functionally and phenotypically heterogeneous populations. Monocyte-derived DCs (moDCs) are a DC subset that have been attracting increasing interest owing to their potent influence on adaptive immune function and their rapid accumulation upon an inflammatory stimulus. Although early studies on moDCs mainly addressed infection, their emergence and function in other settings such as autoimmunity and allogeneic organ transplantation are now being increasingly appreciated. In this review, the relationship between murine monocyte subsets and the moDCs that arise from them is discussed. Their role in initiating and modulating innate and adaptive immune responses in various pathophysiological scenarios is also explored, including how they may separate their labour from conventional DCs. How these findings might relate to their human counterparts is also discussed. Overall, monocytes and moDCs exhibit complex and heterogeneous behaviours that are critical in responses against microbial invasion, autoimmunity and allograft rejection.

ABSTRACT:Antiphospholipid syndrome (APS) may occur in isolation or in association with systemic lupus erythematosus (SLE), with the potential to cause renal failure via several distinct pathologies. Renal transplantation in the presence of APS carries a risk of early graft loss from arterial or venous thrombosis, or thrombotic microangiopathy (TMA). Whilst perioperative anticoagulation reduces the risk of large vessel thrombosis, it may result in significant haemorrhage, and its efficacy in preventing post-transplant TMA is uncertain. Here, we report a patient with end-stage kidney disease (ESKD) due to lupus nephritis and APS, in whom allograft TMA developed soon after transplantation despite partial anticoagulation. TMA resolved with plasma exchangebased therapy albeit with some irreversible graft damage and renal impairment. We discuss the differential diagnosis of post-transplant TMA, and current treatment options.

Although the mechanisms governing the innate recognition of pathogen-associated molecular patterns have been well defined, how allogeneic cellular stimuli evoke innate responses remains less so. In this article, we report that upon i.v. transfer (to avoid major iatrogenic interference), allogeneic but not syngeneic leukocytes could induce a rapid (after 1 d) accumulation of host monocyte–derived dendritic cells (moDCs) without any increase in conventional DCs. This occurred in various donor–host strain combinations, did not require MHC mismatch, and could be induced by various donor cell types including B cells, T cells, or NK cells. Using RAG−/−γc−/− and scid γc−/−mice with different MHC, we found that the presence of either donor or host lymphoid cells was required. Alloinduced moDC accumulation was significantly reduced when splenocytes from mice deficient in NK cells by genetic ablation were used as donors. A major component of this moDC accumulation appears to be recruitment. Our findings provide new insights into how the innate and adaptive immune system may interact during allogeneic encounters and thus transplant rejection.

Summary The optimum approach towards immunosuppression withdrawal following kidney transplant failure is unclear. Prolonged weaning may be associated with reduced sensitization, less graft nephrectomy and greater likelihood of retransplantation, but conversely increased risk of infection, malignancy and death. We conducted a single‐centre retrospective analysis of patients experiencing graft failure between 2007 and 2017, comparing rates of sensitization, retransplantation, nephrectomy, infection, malignancy and death between patients who had immunosuppression weaned over <90 vs. 90–180 vs. >180 days. Patient survival after immunosuppression withdrawal over <90 vs. 90–180 vs. >180 days was 73.3%, 72.1% and 80.4%, respectively (P = 0.35), with no differences in cPRA (80.06 vs. 81.21 vs. 85.42, P = 0.66) or retransplantation rate [24/31 (77.4%) vs. 21/35 (60.0%) vs. 22/36 (61.1%), P = 0.13]. There was significantly less nephrectomy after late immunosuppression cessation [10/42 (23.8%) vs. 7/42 (16.7%) vs. 3/43 (7.0%), P = 0.01] but no differences in infections or malignancy. On competing risk regression (death as competing risk) controlling for cofactors including age, nephrectomy and rejection, prolonged immunosuppression did not predict likelihood of retransplantation (SHR 1.000, P = 0.88). Prolonged immunosuppression withdrawal does not reduce sensitization or improve retransplantation rates but is associated with less nephrectomy. Immunosuppression withdrawal should be tailored to individual circumstances after graft failure.

Thrombotic thrombocytopenic purpura is a rare condition characterized by microangiopathic haemolytic anaemia, thrombocytopenia, altered neurology, renal impairment and fever. While plasma exchange has reduced mortality from more than 90% to between 10 and 30%, a proportion of cases fail to respond. Rituximab may be efficacious in the management of refractory cases of thrombotic thrombocytopenic purpura. We present two cases in which rituximab was used with successful outcomes. Treatment resulted in resolution of severe clinical and haematological abnormalities in both patients. There has been no relapse after 16 months follow up. Our experience supports the use of rituximab in difficult cases of TTP. Ongoing evaluation of its use is in progress at our institution.

ABO-incompatible renal transplant performed with antibody removal and conventional immunosuppression continues to provide excellent patient and graft survival, and stable renal function over 4 years. Coupled with absent transplant glomerulopathy and low rates of progressive IF/TA on earlier biopsies, this suggests that ABOi with conventional immunosuppression and antibody removal, without rituximab or splenectomy, can achieve long-term outcomes comparable to ABO-compatible transplantation.