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Self-tolerance and immune homeostasis are orchestrated by FOXP3+ regulatory T cells (Tregs). Recent data have revealed that upon stimulation, Tregs may exhibit plasticity toward a proinflammatory phenotype, producing interleukin 17 (IL-17) and/or interferon γ (IFN-γ). Such deregulation of Tregs may contribute to the perpetuation of inflammatory processes, including graft-versus-host disease. Thus, it is important to identify immunomodulatory factors influencing Treg stability. Platelet-derived microparticles (PMPs) are involved in hemostasis and vascular health and have recently been shown to be intimately involved in (pathogenic) immune responses. Therefore, we investigated whether PMPs have the ability to affect Treg plasticity. PMPs were cocultured with healthy donor peripheral blood–derived Tregs that were stimulated with anti-CD3/CD28 monoclonal antibodies in the presence of IL-2, IL-15, and IL-1β. PMPs prevented the differentiation of peripheral blood–derived Tregs into IL-17– and IFN-γ–producing cells, even in the presence of the IL-17–driving proinflammatory cytokine IL-1β. The mechanism of action by which PMPs prevent Treg plasticity consisted of rapid and selective P-selectin–dependent binding of PMPs to a CCR6+HLA-DR+ memory-like Treg subset and their ability to inhibit Treg proliferation, in part through CXCR3 engagement. The findings that ∼8% of Tregs in the circulation of healthy individuals are CD41+P-selectin+ and that distinct binding of patient plasma PMPs to Tregs was observed support in vivo relevance. These findings open the exciting possibility that PMPs actively regulate the immune response at sites of (vascular) inflammation, where they are known to accumulate and interact with leukocytes, consolidating the (vascular) healing process.

Self-tolerance and immune homeostasis are orchestrated by FOXP3+regulatory T cells (Tregs). Recent data have revealed that upon stimulation, Tregs may exhibit plasticity toward a proinflammatory phenotype, producing interleukin 17 (IL-17) and/or interferon γ (IFN-γ). Such deregulation of Tregs may contribute to the perpetuation of inflammatory processes, including graft-versus-host disease. Thus, it is important to identify immunomodulatory factors influencing Treg stability. Platelet-derived microparticles (PMPs) are involved in hemostasis and vascular health and have recently been shown to be intimately involved in (pathogenic) immune responses. Therefore, we investigated whether PMPs have the ability to affect Treg plasticity. PMPs were cocultured with healthy donor peripheral blood–derived Tregs that were stimulated with anti-CD3/CD28 monoclonal antibodies in the presence of IL-2, IL-15, and IL-1β. PMPs prevented the differentiation of peripheral blood–derived Tregs into IL-17– and IFN-γ–producing cells, even in the presence of the IL-17–driving proinflammatory cytokine IL-1β. The mechanism of action by which PMPs prevent Treg plasticity consisted of rapid and selective P-selectin–dependent binding of PMPs to a CCR6+HLA-DR+memory-like Treg subset and their ability to inhibit Treg proliferation, in part through CXCR3 engagement. The findings that ∼8% of Tregs in the circulation of healthy individuals are CD41+P-selectin+and that distinct binding of patient plasma PMPs to Tregs was observed support in vivo relevance. These findings open the exciting possibility that PMPs actively regulate the immune response at sites of (vascular) inflammation, where they are known to accumulate and interact with leukocytes, consolidating the (vascular) healing process.

Immunomodulating regulatory T-cell (Treg) therapy is a promising strategy in autoimmunity and transplantation. However, to achieve full clinical efficacy, better understanding of in vivo human Treg biology is warranted. Here, we demonstrate that in contrast to blood and bone marrow Tregs, which showed a resting phenotype, the majority of CD4posCD25posCD127negFoxP3pos Tregs in secondary lymphoid organs were proliferating activated CD69posCD45RAneg cells with a hyperdemethylated FOXP3 gene and a broad T-cell receptor–Vβ repertoire, implying polyclonal activation. Activated CD69pos Tregs were distributed over both T-cell and B-cell areas, distant from Airepos and CD11cpos cells. In contrast to the anergic peripheral blood Tregs, lymphoid organ Tregs had significant ex vivo proliferative capacity and produced cytokines like interleukin-2, while revealing similar suppressive potential. Also, next to Treg-expressing chemokine receptors important for a prolonged stay in lymphoid organs, a significant part of the cells expressed peripheral tissue–associated, functional homing markers. In conclusion, our data suggest that human secondary lymphoid organs aid in the maintenance and regulation of Treg function and homeostasis. This knowledge may be exploited for further optimization of Treg immunotherapy, for example, by ex vivo selection of Tregs with capacity to migrate to lymphoid organs providing an in vivo platform for further Treg expansion.

Immunomodulating regulatory T-cell (Treg) therapy is a promising strategy in autoimmunity and transplantation. However, to achieve full clinical efficacy, better understanding of in vivo human Treg biology is warranted. Here, we demonstrate that in contrast to blood and bone marrow Tregs, which showed a resting phenotype, the majority of CD4posCD25posCD127negFoxP3posTregs in secondary lymphoid organs were proliferating activated CD69posCD45RAnegcells with a hyperdemethylated FOXP3gene and a broad T-cell receptor–Vβ repertoire, implying polyclonal activation. Activated CD69posTregs were distributed over both T-cell and B-cell areas, distant from Aireposand CD11cposcells. In contrast to the anergic peripheral blood Tregs, lymphoid organ Tregs had significant ex vivo proliferative capacity and produced cytokines like interleukin-2, while revealing similar suppressive potential. Also, next to Treg-expressing chemokine receptors important for a prolonged stay in lymphoid organs, a significant part of the cells expressed peripheral tissue–associated, functional homing markers. In conclusion, our data suggest that human secondary lymphoid organs aid in the maintenance and regulation of Treg function and homeostasis. This knowledge may be exploited for further optimization of Treg immunotherapy, for example, by ex vivo selection of Tregs with capacity to migrate to lymphoid organs providing an in vivo platform for further Treg expansion.

Junctional adhesion molecule A (JAM-A) is a transmembrane adhesive glycoprotein that participates in the organization of endothelial tight junctions and contributes to leukocyte transendothelial migration. We demonstrate here that cultured endothelial cells not only express a cellular 43-kDa variant of JAM-A but also release considerable amounts of a 33-kDa soluble JAM-A variant. This release is enhanced by treatment with proinflammatory cytokines and is associated with the down-regulation of surface JAM-A. Inhibition experiments, loss/gain-of-function experiments, and cleavage experiments with recombinant proteases indicated that cleavage of JAM-A is mediated predominantly by the disintegrin and metalloproteinase (ADAM) 17 and, to a lesser extent, by ADAM10. Cytokine treatment of mice increased JAM-A serum level and in excised murine aortas increased ADAM10/17 activity correlated with enhanced JAM-A release. Functionally, soluble JAM-A blocked migration of cultured endothelial cells, reduced transendothelial migration of isolated neutrophils in vitro, and decreased neutrophil infiltration in a murine air pouch model by LFA-1– and JAM-A–dependent mechanisms. Therefore, shedding of JAM-A by inflamed vascular endothelium via ADAM17 and ADAM10 may not only generate a biomarker for vascular inflammation but could also be instrumental in controlling JAM-A functions in the molecular zipper guiding transendothelial diapedesis of leukocytes.

Junctional adhesion molecule A (JAM-A) is a transmembrane adhesive glycoprotein that participates in the organization of endothelial tight junctions and contributes to leukocyte transendothelial migration. We demonstrate here that cultured endothelial cells not only express a cellular 43-kDa variant of JAM-A but also release considerable amounts of a 33-kDa soluble JAM-A variant. This release is enhanced by treatment with proinflammatory cytokines and is associated with the down-regulation of surface JAM-A. Inhibition experiments, loss/gain-of-function experiments, and cleavage experiments with recombinant proteases indicated that cleavage of JAM-A is mediated predominantly by the disintegrin and metalloproteinase (ADAM) 17 and, to a lesser extent, by ADAM10. Cytokine treatment of mice increased JAM-A serum level and in excised murine aortas increased ADAM10/17 activity correlated with enhanced JAM-A release. Functionally, soluble JAM-A blocked migration of cultured endothelial cells, reduced transendothelial migration of isolated neutrophils in vitro, and decreased neutrophil infiltration in a murine air pouch model by LFA-1– and JAM-A–dependent mechanisms. Therefore, shedding of JAM-A by inflamed vascular endothelium via ADAM17 and ADAM10 may not only generate a biomarker for vascular inflammation but could also be instrumental in controlling JAM-A functions in the molecular zipper guiding transendothelial diapedesis of leukocytes.

The effector T-cell lineage shows great plasticity. Th17 cells are acknowledged to be instrumental in the response against microbial infection, but are also associated with autoimmune inflammatory processes. Here, we report that human regulatory T cells (CD4posCD25highFoxp3posCD127negCD27pos) can differentiate into IL-17–producing cells, when stimulated by allogeneic antigen-presenting cells, especially monocytes, in the presence of rhIL-2/rhIL-15. These regulatory T cell (Treg)–derived IL-17–producing cells showed high expression of the Th17-related transcription factor RORγt and were positively identified by CCR6 expression. This differentiation process was enhanced by exogenous IL-1β, IL-23, and IL-21, whereas IL-6 or TGFβ did not affect the emergence of IL-17–producing cells. The addition of IL-1 receptor antagonist (IL-1Ra), but not anti–IL-23 antibody, reduced IL-17–producing cell numbers. When an histone deacetylase (HDAC) inhibitor trichostatin A (TSA) was evaluated, we found a profound negative effect on the emergence of IL-17–producing cells from Tregs, implying that Treg differentiation into IL-17–producing cells depends on histone/protein deacetylase activity. Thus, the data suggest that epigenetic modification underlies the phenomenon of Treg plasticity here described.

The effector T-cell lineage shows great plasticity. Th17 cells are acknowledged to be instrumental in the response against microbial infection, but are also associated with autoimmune inflammatory processes. Here, we report that human regulatory T cells (CD4posCD25highFoxp3posCD127negCD27pos) can differentiate into IL-17–producing cells, when stimulated by allogeneic antigen-presenting cells, especially monocytes, in the presence of rhIL-2/rhIL-15. These regulatory T cell (Treg)–derived IL-17–producing cells showed high expression of the Th17-related transcription factor RORγt and were positively identified by CCR6 expression. This differentiation process was enhanced by exogenous IL-1β, IL-23, and IL-21, whereas IL-6 or TGFβ did not affect the emergence of IL-17–producing cells. The addition of IL-1 receptor antagonist (IL-1Ra), but not anti–IL-23 antibody, reduced IL-17–producing cell numbers. When an histone deacetylase (HDAC) inhibitor trichostatin A (TSA) was evaluated, we found a profound negative effect on the emergence of IL-17–producing cells from Tregs, implying that Treg differentiation into IL-17–producing cells depends on histone/protein deacetylase activity. Thus, the data suggest that epigenetic modification underlies the phenomenon of Treg plasticity here described.

The induction of transplantation tolerance involves a T-cell–mediated process of immune regulation. In clinical transplantation, the use of immunosuppressive drugs that promote or facilitate this process would be highly desirable. Here, we investigated the tolerance-promoting potential of the immunosuppressive drug FK778, currently under development for clinical therapy. Using a human allogeneic in vitro model we showed that, upon T-cell receptor (TCR) triggering, FK778 induced a regulatory phenotype in CD4+CD25− T cells. Purified CD4+CD25− T cells primed in the presence of FK778 showed hyporesponsiveness upon restimulation with alloantigen in the absence of the drug. This anergic state was reversible by exogenous interleukin-2 (IL-2) and was induced independent of naturally occurring CD4+CD25+ regulatory T cells. Pyrimidine restriction was a crucial requirement for the de novo induction of regulatory activity by FK778. The FK778-induced anergic cells showed suppressor activity in a cell-cell contact–dependent manner; were CD25high, CD45RO+, CD27−, and CD62L−; and expressed cytotoxic T-lymphocyte–associated antigen-4 (CTLA-4), glucocorticoid-induced tumor necrosis factor receptor (GITR), and FoxP3. The cells revealed delayed p27kip1 degradation and enhanced phosphorylation of STAT3. In conclusion, the new drug FK778 shows tolerizing potential through the induction of a regulatory T-cell subset in CD4+CD25− T cells.

The induction of transplantation tolerance involves a T-cell–mediated process of immune regulation. In clinical transplantation, the use of immunosuppressive drugs that promote or facilitate this process would be highly desirable. Here, we investigated the tolerance-promoting potential of the immunosuppressive drug FK778, currently under development for clinical therapy. Using a human allogeneic in vitro model we showed that, upon T-cell receptor (TCR) triggering, FK778 induced a regulatory phenotype in CD4+CD25−T cells. Purified CD4+CD25−T cells primed in the presence of FK778 showed hyporesponsiveness upon restimulation with alloantigen in the absence of the drug. This anergic state was reversible by exogenous interleukin-2 (IL-2) and was induced independent of naturally occurring CD4+CD25+regulatory T cells. Pyrimidine restriction was a crucial requirement for the de novo induction of regulatory activity by FK778. The FK778-induced anergic cells showed suppressor activity in a cell-cell contact–dependent manner; were CD25high, CD45RO+, CD27−, and CD62L−; and expressed cytotoxic T-lymphocyte–associated antigen-4 (CTLA-4), glucocorticoid-induced tumor necrosis factor receptor (GITR), and FoxP3. The cells revealed delayed p27kip1degradation and enhanced phosphorylation of STAT3. In conclusion, the new drug FK778 shows tolerizing potential through the induction of a regulatory T-cell subset in CD4+CD25−T cells.

The immunosuppressive drugs rapamycin and cyclosporin A (CsA) are widely used to prevent allograft rejection. Moreover, they were shown to be instrumental in experimental models of tolerance induction. However, it remains to be elucidated whether these drugs have an effect on the CD4+CD25+regulatory T-cell (TREG) population, which plays an important role in allograft tolerance. Recently, we reported that alloantigen-driven expansion of human CD4+CD25+TREGs gives rise to a distinct highly suppressive CD27+TREGsubset next to a moderately suppressive CD27-TREGsubset. In the current study we found that rapamycin and CsA do not interfere with the suppressive activity of human naturally occurring CD4+CD25+T cells. However, in contrast to CsA, rapamycin preserved the dominance of the potent CD27+TREGsubset over the CD27-TREGsubset after alloantigen-driven expansion of CD4+CD25+TREGs in vitro. Accordingly, CD4+CD25+TREGs cultured in the presence of rapamycin displayed much stronger suppressive capacity than CD4+CD25+TREGs cultured in the presence of CsA. In addition, CD4+CD25+TREGcells cultured in the presence of rapamycin, but not CsA, were able to suppress ongoing alloimmune responses. This differential effect of rapamycin and CsA on the CD27+TREGsubset dominance may favor the use of rapamycin in tolerance-inducing strategies.

The immunosuppressive drugs rapamycin and cyclosporin A (CsA) are widely used to prevent allograft rejection. Moreover, they were shown to be instrumental in experimental models of tolerance induction. However, it remains to be elucidated whether these drugs have an effect on the CD4+CD25+ regulatory T-cell (TREG) population, which plays an important role in allograft tolerance. Recently, we reported that alloantigen-driven expansion of human CD4+CD25+ TREGs gives rise to a distinct highly suppressive CD27+TREG subset next to a moderately suppressive CD27-TREG subset. In the current study we found that rapamycin and CsA do not interfere with the suppressive activity of human naturally occurring CD4+CD25+ T cells. However, in contrast to CsA, rapamycin preserved the dominance of the potent CD27+TREG subset over the CD27-TREG subset after alloantigen-driven expansion of CD4+CD25+ TREGs in vitro. Accordingly, CD4+CD25+ TREGs cultured in the presence of rapamycin displayed much stronger suppressive capacity than CD4+CD25+ TREGs cultured in the presence of CsA. In addition, CD4+CD25+ TREG cells cultured in the presence of rapamycin, but not CsA, were able to suppress ongoing alloimmune responses. This differential effect of rapamycin and CsA on the CD27+TREG subset dominance may favor the use of rapamycin in tolerance-inducing strategies.

The chemokines platelet factor 4 (PF4) and RANTES (regulated on activation normal T cell expressed and secreted) are secreted by activated platelets and influence multiple cell types and biologic processes. For instance, PF4 inhibits progenitor cell proliferation and angiogenesis, while platelet-derived RANTES is involved in vascular recruitment of monocytes. However, little is known about functional interactions of PF4 and RANTES. Here we show that the presence of PF4 enhanced the arrest of RANTES-stimulated monocytes and monocytic cells on activated endothelial cells under flow conditions, while binding of PF4 to the monocyte surface was increased by RANTES. Both RANTES-triggered arrest and PF4 binding involved monocytic chondroitin sulfate. Ligand blots and surface plasmon resonance revealed a robust heterophilic interaction of PF4 with RANTES but not with RANTES variants defective in higher order oligomerization. The tetrameric mutant E26A bound to the monocyte surface without increasing PF4 binding, and monocyte arrest induced by E26A-RANTES was not enhanced by PF4. Stimulation of monocytes with supernatants of activated platelets triggered arrest involving RANTES and PF4, as shown by inhibition studies. Our results suggest that heterophilic interactions with PF4 require structural motifs important in RANTES oligomerization and amplify RANTES-triggered effects on monocyte adhesion. This may have implications for the modulation of inflammatory recruitment by platelet-derived chemokines.

The chemokines platelet factor 4 (PF4) and RANTES (regulated on activation normal T cell expressed and secreted) are secreted by activated platelets and influence multiple cell types and biologic processes. For instance, PF4 inhibits progenitor cell proliferation and angiogenesis, while platelet-derived RANTES is involved in vascular recruitment of monocytes. However, little is known about functional interactions of PF4 and RANTES. Here we show that the presence of PF4 enhanced the arrest of RANTES-stimulated monocytes and monocytic cells on activated endothelial cells under flow conditions, while binding of PF4 to the monocyte surface was increased by RANTES. Both RANTES-triggered arrest and PF4 binding involved monocytic chondroitin sulfate. Ligand blots and surface plasmon resonance revealed a robust heterophilic interaction of PF4 with RANTES but not with RANTES variants defective in higher order oligomerization. The tetrameric mutant E26A bound to the monocyte surface without increasing PF4 binding, and monocyte arrest induced by E26A-RANTES was not enhanced by PF4. Stimulation of monocytes with supernatants of activated platelets triggered arrest involving RANTES and PF4, as shown by inhibition studies. Our results suggest that heterophilic interactions with PF4 require structural motifs important in RANTES oligomerization and amplify RANTES-triggered effects on monocyte adhesion. This may have implications for the modulation of inflammatory recruitment by platelet-derived chemokines.

Protein S exhibits anticoagulant activity independent of activated protein C (APC). An automated factor Xa–based one-stage clotting assay was developed that enables quantification of the APC-independent activity of protein S in plasma from the ratio of clotting times (protein S ratio [pSR]) determined in the absence and presence of neutralizing antibodies against protein S. The pSR was 1.62 ± 0.16 (mean ± SD) in a healthy population (n = 60), independent of plasma levels of factors V, VIII, IX, and X; protein C; and antithrombin, and not affected by the presence of factor V Leiden. The pSR strongly correlates with the plasma level of protein S and is modulated by the plasma prothrombin concentration. In a group of 16 heterozygous protein S–deficient patients, the observed mean pSR (1.31 ± 0.09) was significantly lower than the mean pSR of the healthy population, as was the pSR of plasma from carriers of the prothrombin G20210A mutation (1.47 ± 0.21; n = 46). We propose that the decreased APC-independent anticoagulant activity of protein S in plasma with elevated prothrombin levels may contribute to the thrombotic risk associated with the prothrombin G20210A mutation.

Protein S exhibits anticoagulant activity independent of activated protein C (APC). An automated factor Xa–based one-stage clotting assay was developed that enables quantification of the APC-independent activity of protein S in plasma from the ratio of clotting times (protein S ratio [pSR]) determined in the absence and presence of neutralizing antibodies against protein S. The pSR was 1.62 ± 0.16 (mean ± SD) in a healthy population (n = 60), independent of plasma levels of factors V, VIII, IX, and X; protein C; and antithrombin, and not affected by the presence of factor V Leiden. The pSR strongly correlates with the plasma level of protein S and is modulated by the plasma prothrombin concentration. In a group of 16 heterozygous protein S–deficient patients, the observed mean pSR (1.31 ± 0.09) was significantly lower than the mean pSR of the healthy population, as was the pSR of plasma from carriers of the prothrombin G20210A mutation (1.47 ± 0.21; n = 46). We propose that the decreased APC-independent anticoagulant activity of protein S in plasma with elevated prothrombin levels may contribute to the thrombotic risk associated with the prothrombin G20210A mutation.

The generation of immunoregulatory T cells that block the B7(CD86/CD80)-CD28 and/or CD40-CD154 costimulatory pathways has great potential for the induction of long-term transplantation tolerance. In a human polyclonal in vitro model, combined monoclonal antibody (mAb) blocking of the costimulatory ligands CD40 and CD86 lead to allospecific T-cell anergy that cannot be reversed by antigenic rechallenge in the presence of IL-2. Although antigenic restimulation with IL-2 restored the proliferative response, subsequent antigenic restimulation of the restored anergic cells in a tertiary mixed lymphocyte culture still resulted in nonresponsiveness. Importantly, these anergic T cells suppress the response of naive alloreactive T cells in an antigen-specific way via linked recognition. Suppression may partially depend on local IL-10 production, while transforming growth factor–ß (TGF-ß) did not play a role. Irrespective of the monoclonal antibody combination used, blast formation occurred in a subset of CD4+ cells. These cells were characterized by a sustained CD45RA expression, an increased T-cell receptor density, and a lower level of CD4 expression. A reduced number of CD45RO+/CD8+ T cells was observed whenever anti-CD86 was combined with anti-CD40, which was reflected by an even more attenuated cytotoxic T-cell function. This indicates the importance of CD40-CD154 in the generation of cytotoxic T cells in this transplantation model. We hypothesize that in our model, anergy is induced in the CD4+ T-cell subset, whereby CD8+ cytotoxic effector function is impaired by the lack of both CD40-CD154 signaling and cytokine-mediated help. This costimulatory ligand–directed mAb approach might well be used for the ex vivo generation of antigen-specific immunoregulatory T cells applicable in adoptive immunotherapy.

Background

Cloos: Takeda: Research Funding; Helsinn: Other: MRD assessments; Navigate: Patents & Royalties: Royalties for MRD analyses; DC-One: Other: MRD assessments, Research Funding; Genentech: Research Funding; Janssen: Research Funding; Novartis: Consultancy, Other: MRD assessments, Research Funding; Astellas: Speakers Bureau; Merus: Other: MRD assessments, Research Funding. Montesinos: Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Forma Therapeutics: Consultancy; Stemline/Menarini: Consultancy; Teva: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Tolero Pharmaceutical: Consultancy; Glycomimetics: Consultancy; Sanofi: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Pfizer: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Incyte: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Daiichi Sankyo: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Karyopharm: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Agios: Consultancy; AbbVie: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Astellas Pharma, Inc.: Consultancy, Honoraria, Other: Advisory board, Research Funding, Speakers Bureau. Fiedler: Daiichi Sankyo: Consultancy, Other: support for meeting attendance; Pfizer: Consultancy, Research Funding; Celgene: Consultancy; Morphosys: Consultancy; Abbvie: Consultancy, Honoraria; Jazz Pharmaceuticals: Consultancy, Other: support for meeting attendance; Amgen: Consultancy, Other: support for meeting attendance, Patents & Royalties, Research Funding; Servier: Consultancy, Other: support for meeting attendance; Stemline: Consultancy; Novartis: Consultancy; ARIAD/Incyte: Consultancy. Müller: GSK: Consultancy; Janssen: Other: Honoraria for educational event; Celgene/BMS: Honoraria; Abbvie: Honoraria; Jazz: Honoraria; Amgen: Honoraria; Sandoz/Novartis: Honoraria; Sanofi: Honoraria; Takeda: Honoraria. Sica: Pfizer: Honoraria. Westermann: Astellas: Honoraria; Pfizer: Consultancy, Honoraria; Abbvie: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; BMS: Honoraria; Novartis: Consultancy, Honoraria; Sanofi: Consultancy, Honoraria; Stem Cell Line: Consultancy, Honoraria. Döhner: Pfizer: Research Funding; Jazz: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria; Helsinn: Consultancy, Honoraria; Berlin-Chemie: Consultancy, Honoraria; Agios: Consultancy, Honoraria, Research Funding; Abbvie: Consultancy, Honoraria, Research Funding; Gilead: Consultancy, Honoraria; Roche: Consultancy, Honoraria; Amgen: Consultancy, Honoraria, Research Funding; Astellas: Consultancy, Honoraria, Research Funding; Astex: Consultancy, Honoraria; AstraZeneca: Consultancy, Honoraria; Celgene: Consultancy, Honoraria, Research Funding; GEMoaB: Consultancy, Honoraria; Bristol Myers Squibb: Consultancy, Honoraria, Research Funding; Ulm University Hospital: Current Employment; Novartis: Consultancy, Honoraria, Research Funding; Oxford Biomedicals: Consultancy, Honoraria. Levis: Pfizer: Consultancy, Honoraria; Jazz: Consultancy, Honoraria; BMS: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen, Astellas Pharma, Daiichi-Sankyo, FujiFilm, and Menarini: Honoraria; Astellas and FujiFilm: Research Funding; Takeda: Honoraria. Ossenkoppele: Jazz: Consultancy, Honoraria; Abbvie, AGIOS, BMS/Celgene Astellas,AMGEN, Gilead,Servier,JAZZ,Servier Novartis: Consultancy, Honoraria; Agios: Consultancy, Honoraria; BMS/Celgene: Consultancy, Honoraria; Astellas: Consultancy, Honoraria; Gilead: Consultancy, Honoraria; Servier: Consultancy, Honoraria. Stone: Astellas: Membership on an entity's Board of Directors or advisory committees; Onconova: Consultancy; Aprea: Consultancy; Amgen: Membership on an entity's Board of Directors or advisory committees; AbbVie: Consultancy; Actinium: Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Consultancy; Bristol Myers Squibb: Consultancy; Elevate Bio: Membership on an entity's Board of Directors or advisory committees; Foghorn Therapeutics: Consultancy; Innate: Consultancy; Janssen: Consultancy; Jazz: Consultancy; Celgene: Consultancy; Boston Pharmaceuticals: Consultancy; BerGen Bio: Membership on an entity's Board of Directors or advisory committees; Gemoab: Membership on an entity's Board of Directors or advisory committees; Syros: Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy; Agios: Consultancy, Research Funding; Macrogenics: Consultancy; Syndax: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Research Funding; Syntrix/ACI: Membership on an entity's Board of Directors or advisory committees; Arog: Consultancy, Research Funding. Koenen: Novartis Pharma AG: Current Employment. Bengoudifa: Novartis Pharma AG: Current Employment. Cheng: Novartis Pharmaceuticals Corporation: Current Employment. Medts: Novartis Pharma AG: Current Employment. Heidinger: Novartis Pharma AG: Current Employment. Sachs: Novartis Pharma AG: Current Employment. Sierra: Janssen: Other: Educational grant; Astellas: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Roche: Other: Educational grant; Amgen: Other: Educational grant; Pfizer: Honoraria; BMS Celgene: Honoraria, Research Funding; Abbvie: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Honoraria, Research Funding, Speakers Bureau; Alexion: Other: Educational grant; Jazz Pharmaceuticals: Research Funding.

No relevant conflicts of interest to declare.

Background: The Kunitz type tissue factor pathway inhibitor (TFPI) is an important regulator in hemostasis. Decreased concentrations are a risk factor for thrombosis and complete TFPI deficiency is associated with lethality. TFPI is also reported to be an important link between inflammation and thrombosis. Neutrophil extracellular traps (NETs) formed by NETosis can bind TFPI which then can be cleaved and inactivated by neutrophil elastase (NE) during thrombotic events. In neutrophils, the enzyme peptide arginine deiminase 4 (PAD4) is central in the citrullination of histones prior to the externalization of DNA during NETosis. In this study, we provide evidence that PAD4 also might regulate the activity of TFPI by posttranslational modification of its functional arginines into citrulline.

Abstract 103

Besides its well-known role in initiation and propagation of thrombus formation, thrombin may have multiple pro-atherogenic actions.Pharmacologic thrombin inhibition attenuates the onset and progression of atherosclerosis and favors plaque stability in hypercoagulable mice prone to aggressive atherosclerosis development.Hypercoagulability in TMPro/Pro:ApoE−/− mice resulted in severe atherosclerotic burden formation compared to ApoE−/− mice (389.1*103 μm2 vs. 187.0*103 μm2, p<0.0005). Pro-coagulant mice showed larger necrotic cores, decreased plaque collagen content, vast stenosis (up to 90%) and enhanced outward remodeling. Hypercoagulability markedly increased systemic and vascular inflammation, represented by significantly higher CXCL1, MCP-1 and G-CSF plasma levels, pronounced neutrophilia, enhanced Ly6G+ cells arrest to carotid plaques, increased neutrophil recruitment (IHC/Intravital Microscopy), massive intraplaque hemorrhage and spontaneous plaque ruptures. Genetically diminished prothrombin levels (FII-/WT:ApoE−/− mice) caused a significant decrease in atherosclerosis (72.5*103 μm2 vs. 128.4*103 μm2, p<0.01) with a pronounced stable phenotype with less/smaller necrotic cores, thicker fibrous caps and abundant collagen and vascular smooth muscle cell content. Ly6G+ cell intraplaque recruitment was reduced and white blood cell counts and IL-6 levels (3.8±1.66 vs. 8.8±5.34 pg/mL, p<0.05) were diminished compared to control mice. Remarkably, administration of the oral direct thrombin inhibitor Dabigatran etexilate or the anticoagulant activated protein C (APC) in TMPro/Pro:ApoE−/− mice reduced lesions formation by > 80%, suppressed leukocyte recruitment, enhanced plaque stability, whereas numerous pro-inflammatory cytokines were diminished to levels comparable to non-atherosclerotic mice.These data establish a pivotal role for thrombin generation in controlling the level of inflammation related to atherosclerosis development in ApoE−/− mice. The potential clinical impact of long term administration of novel classes of anticoagulants on atherosclerosis merits further study.Weiler: BloodCenter of Wisconsin: Patents & Royalties. van Ryn:Boehringer Ingelheim Pharma GmbH & Co KG: Employment.