C5aR1 regulates migration of suppressive myeloid cells required for costimulatory blockade-induced murine allograft survival

Abstract

Costimulatory blockade-induced murine cardiac allograft survival requires intragraft accumulation of CD11b Ly6C Ly6G regulatory myeloid cells (Mregs) that expand regulatory T cells (Tregs) and suppress effector T cells (Teffs). We previously showed that C5a receptor (C5aR1) signaling on T cells activates Teffs and inhibits Tregs, but whether and/or how C5aR1 affects Mregs required for transplant survival is unknown. Although BALB/c hearts survived >60 days in anti-CD154 (MR1)-treated or cytotoxic T-lymphocyte associated protein 4 (CTLA4)-Ig-treated wild-type (WT) recipients, they were rejected at ~30 days in MR1-treated or CTLA4-Ig-treated recipients selectively deficient in C5aR1 restricted to myeloid cells (C5ar1 xLysM-Cre). This accelerated rejection was associated with ~2-fold more donor-reactive T cells and ~40% less expansion of donor-reactive Tregs. Analysis of graft-infiltrating mononuclear cells on posttransplant day 6 revealed fewer Ly6C monocytes in C5ar1 xLysM-Cre recipients. Expression profiling of intragraft Ly6C monocytes showed that C5aR1 deficiency downregulated genes related to migration/locomotion without changes in genes associated with suppressive function. Cotransfer of C5ar1 and C5ar1 xLysM-Cre myeloid cells into MR1-treated allograft recipients resulted in less accumulation of C5ar1 cells within the allografts, and in vitro assays confirmed that Ly6C myeloid cells migrate to C5a/C5aR1-initiated signals. Together, our results newly link myeloid cell-expressed C5aR1 to intragraft accumulation of myeloid cells required for prolongation of heart transplant survival induced by costimulatory blockade.

Absence of recipient C3aR1 signaling limits expansion and differentiation of alloreactive CD8+ T cell immunity and prolongs murine cardiac allograft survival

“…These assays showed ~10-fold fewer splenic IFNγ + , TNFα + and CD107 + CD8 + T cells vs. the untreated recipients on day 6 (regardless of C3aR1 expression, compare to Figure 1) and demonstrated that spleens obtained from the tacrolimus-treated C3ar1 −/− recipients contained significantly fewer donor-reactive IFNγ + (Figure 2B top, 2C), TNFα + (Figure 2B bottom, 2D), and CD107a/b + (Figure 2E) CD8 + T cells than tacrolimustreated WT controls. While we observed no differences in T REG numbers between groups, ( Figure 2F), calculated donor-reactive, IFNγ-or TNFα-producing T EFF :T REG ratios ( Figure 2G-H) were lower in the C3ar1 −/− recipients, indicative of enhanced T REG function (34). We similarly observed 2-fold lower numbers of IFNγ + , TNFα + and CD107 + splenic CD8 + T cells in the day 10 post-transplant tacrolimus+C3aR1-A treated recipients vs. tacrolimus treated controls (p<0.05 for each, n=4/group, data not shown).…”

Role of Complement Activation in Allograft Inflammation

“…Using novel myeloid-cell specific C5aR1 conditional knockout mice, Llaudo et al showed C5a/C5aR1 signaling on myeloid cells is a key mediator of regulatory myeloid cell induction/function post-transplant. Absence of C5aR1 specifically on myeloid cells (and not granulocytes) increased anti-donor T cell immunity, decreased T REG , and accelerated graft rejection despite costimulatory blockade (43).…”

23rd Nantes Actualités Transplantation: “Genomics and Immunogenetics of Kidney and Inflammatory Diseases—Lessons for Transplantation”

“…44 The development of drugs blocking the complement, such as eculizumab that targets C5, could not only improve the management of aHUS 45 but also kidney transplantrelated complications. 44,46 Multiple fields have been renovated by growing knowledge of diverse mutation of clinical interest. Corinne Antignac's (Inserm U1163, Paris, France) presentation focused specifically on hereditary forms of focal segmental glomerulosclerosis (FSGS), a podocytopathy associated with proteinuria.…”