Morphometric Analysis of Neointimal Formation in Murine Cardiac Allografts1

Macrophages infiltrating the allografts are heterogeneous, consisting of proinflammatory (M1 cells) as well as antiinflammatory and fibrogenic phenotypes (M2 cells); they affect transplantation outcomes via diverse mechanisms. Here we found that macrophage polarization into M1 and M2 subsets was critically dependent on tumor necrosis factor receptor-associated factor 6 (TRAF6) and mammalian target of rapamycin (mTOR), respectively. In a heart transplant model we showed that macrophage-specific deletion of TRAF6 (LysM Traf6 ) or mTOR (LysM Mtor ) did not affect acute allograft rejection. However, treatment of LysM Mtor recipients with CTLA4-Ig induced long-term allograft survival (>100 days) without histological signs of chronic rejection, whereas the similarly treated LysM Traf6 recipients developed severe transplant vasculopathy (chronic rejection). The presentation of chronic rejection in CTLA4-Ig-treated LysM Traf6 mice was similar to that of CTLA4-Ig-treated wild-type B6 recipients. Mechanistically, we found that the graft-infiltrating macrophages in LysM Mtor recipients expressed high levels of PD-L1, and that PD-L1 blockade readily induced rejection of otherwise survival grafts in the LysM Mtor recipients. Our findings demonstrate that targeting mTOR-dependent M2 cells is critical for preventing chronic allograft rejection, and that graft survival under such conditions is dependent on the PD-1/PD-L1 coinhibitory pathway.

Section: Methodsmentioning

confidence: 99%

Macrophage subpopulations and their impact on chronic allograft rejection versus graft acceptance in a mouse heart transplant model

Zhao

Chen

Lan

et al. 2018

“…The software then quantitated the manually demarcated luminal and intimal areas. From these area values the “neointimal index”, defined as neointimal area divided by neointimal area plus luminal area multiplied by 100, was calculated similar to what has been described previously (24). A higher value of the neointimal index indicates a more severe coronary lesion with 100 being complete occlusion.…”

Section: Methodsmentioning

confidence: 99%

A Novel Pathway of Chronic Allograft Rejection Mediated by NK Cells and Alloantibody

Hirohashi

Chase

Pelle

et al. 2012

213

163

Chronic allograft vasculopathy (CAV) in murine heart allografts can be elicited by adoptive transfer of donor specific antibody (DSA) to class I MHC antigens and is independent of complement. Here we address the mechanism by which DSA causes CAV. B6.RAG1−/− or B6.RAG1−/−C3−/− (H-2b) mice received B10.BR (H-2k) heart allografts and repeated doses of IgG2a, IgG1 or F(ab’)2 fragments of IgG2a DSA (anti-H-2k). Intact DSA regularly elicited markedly stenotic CAV in recipients over 28 days. In contrast, depletion of NK cells with anti-NK1.1 reduced significantly DSA-induced CAV, as judged morphometrically. Recipients genetically deficient in mature NK cells (γ-chain knock out) also showed decreased severity of DSA-induced CAV. Direct NK reactivity to the graft was not necessary. F(ab’)2 DSA fragments, even at doses twofold higher than intact DSA, were inactive. Graft microvascular endothelial cells responded to DSA in vivo by increased expression of phospho-extracellular signal-regulated kinase (pERK), a response not elicited by F(ab’)2 DSA. We conclude that antibody mediates CAV through NK cells, by an Fc dependent manner. This new pathway adds to the possible mechanisms of chronic rejection and may relate to the recently described C4d-negative chronic antibody-mediated rejection in humans.

“…The software then quantitated the manually demarcated luminal and intimal areas. From these area values the ‘neointimal index’ or percent of luminal encroachment, defined as neointimal area divided by neointimal area plus luminal area 100×, was calculated, similar to what has been described previously (27). A higher value of the neointimal index indicates a more severe coronary lesion (100% = completely occluded).…”

Section: Methodsmentioning

confidence: 99%

Complement Independent Antibody‐Mediated Endarteritis and Transplant Arteriopathy in Mice

Hirohashi

Uehara

Chase

et al. 2010

101

Complement fixation, as evidenced by C4d in the microvasculature, is a widely accepted criterion of antibody-mediated rejection. Complement fixation has been shown to be essential in acute antibody-mediated rejection, but its role in chronic rejection has not been addressed. Previous studies showed that passive transfer of complement fixing monoclonal IgG2a anti-H-2Kk into B6.RAG1−/− KO recipients of B10.BR hearts led to progressive chronic transplant arteriopathy (CTA) over 14–28 days, accompanied by C4d deposition. The present studies were designed to test whether complement was required for these lesions. We report that a noncomplement fixing donor-specific alloantibody (DSA, monoclonal IgG1 anti-H-2Kk) injected into B6.RAG1−/− KO recipients of B10.BR hearts also promotes CTA, without C4d deposition. Furthermore, a passive transfer of DSA (monoclonal IgG2a anti-H-2Kk) initiated endarteritis followed by CTA in B6.RAG1−/− mice genetically deficient in the third component of complement (RAG1−/−C3−/−). These studies indicate that antibody to class I MHC antigens can trigger chronic arterial lesions in vivo without complement participation, in contrast to acute antibody-mediated rejection. This pathway may be relevant to C4d-negative chronic rejection sometimes observed in patients with DSA, and argues that lack of C4d deposition does not exclude antibody-mediated chronic rejection.