Remodeling of the mononuclear phagocyte network underlies chronic inflammation and disease progression in heart failure: critical importance of the cardiosplenic axis.

RATIONALE: The role of mononuclear phagocytes in chronic heart failure (HF) is unknown. OBJECTIVE: Our aim was to delineate monocyte, macrophage, and dendritic cell trafficking in HF and define the contribution of the spleen to cardiac remodeling. METHODS AND RESULTS: We evaluated C57Bl/6 mice with chronic HF 8 weeks after coronary ligation. As compared with sham-operated controls, HF mice exhibited: (1) increased proinflammatory CD11b+ F4/80+ CD206- macrophages and CD11b+ F4/80+ Gr-1(hi) monocytes in the heart and peripheral blood, respectively, and reduced CD11b+ F4/80+ Gr-1(hi) monocytes in the spleen; (2) significantly increased CD11c+ B220- classical dendritic cells and CD11c+ low)B220+ plasmacytoid dendritic cells in both the heart and spleen, and increased classic dendritic cells and plasmacytoid dendritic cells in peripheral blood and bone marrow, respectively; (3) increased CD4+ helper and CD8+ cytotoxic T-cells in the spleen; and (4) profound splenic remodeling with abundant white pulp follicles, markedly increased size of the marginal zone and germinal centers, and increased expression of alarmins. Splenectomy in mice with established HF reversed pathological cardiac remodeling and inflammation. Splenocytes adoptively transferred from mice with HF, but not from sham-operated mice, homed to the heart and induced long-term left ventricular dilatation, dysfunction, and fibrosis in naive recipients. Recipient mice also exhibited monocyte activation and splenic remodeling similar to HF mice. CONCLUSIONS: Activation of mononuclear phagocytes is central to the progression of cardiac remodeling in HF, and heightened antigen processing in the spleen plays a critical role in this process. Splenocytes (presumably splenic monocytes and dendritic cells) promote immune-mediated injurious responses in the failing heart and retain this memory on adoptive transfer.

[Organ transplantation and blood transfusion]. / Transfusion sanguine et transplantation.

Pretransplant blood transfusion remains a controversial subject and its history can summarize the last 40 years of transplantation. Until 1971, transfusions were widely used in patients awaiting transplantation, especially due to the anemia induced by the chronic renal dysfunction. Then, a noxious effect of preformed anti-HLA antibodies on renal grafts survival was reported and pretransplant transfusions were stopped. Between 1972 and 1977, improvement of renal graft survival in patients who received pretransplant transfusions was noted. Therefore, from 1978 on, a systematic policy of pretransplant transfusions was adopted by almost all centres of transplantation. During the eighties, it was again abandoned for several reasons: absence of graft survival improvement in patients treated by cyclosporine, HLA immunization leading to an increased incidence of acute graft rejection, risk of viral diseases transmission and human recombinant erythropoietin development. The lack of improvement in graft survival for ten years has been leading the transplant community to look for antigen-specific immunosuppressive strategies to achieve transplantation tolerance. Donor-specific transfusion may have clinical benefits, as long-term grafts survival improvement, through modulation of the recipient's cellular immune system and has been recently reconsidered, especially before living donor transplantation. The immunological mechanisms inducing a tolerance-gaining effect of transfusions are still misunderstood, but the recent discovery of immunomodulatory effects of the apoptotic cells present in cellular products could enlighten our comprehension of pretransplant transfusions benefits and could help to develop specific tolerance induction strategies in solid organ transplantation.

Probing in vivo origins of mononuclear phagocytes by conditional ablation and reconstitution.

Dendritic cells (DCs) and macrophages (MPhis), collectively termed mononuclear phagocytes (MP), are crucial for homeostatic tissue maintenance as well as the innate and adaptive host defense. These pleiotropic functions are likely to be covered by distinct DC and MPhi subsets, defined by anatomic location and molecular make-up. However, task division within the MP system remains poorly defined. A key to understanding of this issue, which might have important implications for the development of future therapeutic strategies, is the elucidation of the in vivo origins of DCs and MPhis, whose study recently gained striking momentum. Here we present methods to investigate the role of MP progenitors, such as monocytes and MPhi/DC precursors (MDPs), in the replenishment of the peripheral MP system.

Effect of transplantation of immunocompetent cell on orientation and exploratory behavior and cytokine gene expression in the brain of experimental animals.

Intravenous injection of adherent splenocyte fraction from donor (CBAxC57Bl/6)F(1) mice characterized by specific open-field behavior modified this behavior in syngeneic recipient mice. This was paralleled by appropriate changes in the levels of IL-1b and type 1 IL-1 receptor mRNA in the brain cells of recipient mice. Hence, we demonstrated the possibility of directed regulation of orientation and exploratory behavior in mice by transplantation of immunocompetent cells. Mononuclear phagocytes play an important role in this phenomenon.

Application of noninvasive phagocytic cellular assays using autologous monocytes to assess red cell alloantibodies in sickle cell patients.

We investigated red cell (RBC) alloantibodies in 125 sickle cell anemia (SCA) patients using tube indirect antiglobulin test (PEG, LISS or enzyme) and gel centrifugation test (LISS or enzyme). Prediction of clinical significance of alloantibodies was evaluated by the monocyte monolayer assay (MMA) and the chemiluminescence test (CLT) using autologous monocytes. The alloimmunization rate was 20.8% and the gel test detected a higher number of alloantibodies than the tube test (26 v 21, p = 0.02). We observed 58.3% and 69.2% positive MMA and CLT results, respectively. Eighteen (69.2%) antibodies exhibited clinical relevance, 14 (58.3%) antibodies reacted by both MMA and CLT, while 4 (15.4%) antibodies reacted only by CLT. In conclusion, the application of phagocytic cellular assays using autologous monocytes defined clinical significance of about 70% of RBC alloantibodies detected in SCA patients. The data also suggest that the CLT may be more valuable than the MMA as a noninvasive test for predicting hemolysis after transfusion of incompatible blood in SCA patients.

Mononuclear phagocyte xanthine oxidoreductase contributes to cytokine-induced acute lung injury.

Acute lung injury (ALI) is characterized by increased alveolar cytokines, inflammatory cell infiltration, oxidative stress, and alveolar cell apoptosis. Previous work suggested that xanthine oxidoreductase (XOR) may contribute to oxidative stress in ALI as a product of the vascular endothelial cell. We present evidence that cytokine induced lung inflammation and injury involves activation of XOR in the newly recruited mononuclear phagocytes (MNP). We found that XOR was increased predominantly in the MNP that increase rapidly in the lungs of rats that develop ALI following intratracheal cytokine insufflation. XOR was recovered from the MNP largely converted to its oxygen radical generating, reversible O-form, and alveolar MNP exhibited increased oxidative stress as evidenced by increased nitrotyrosine staining. Cytokine insufflation also increased alveolar cell apoptosis. A functional role for XOR in cytokine-induced inflammation was demonstrated when feeding rats two different XOR inhibitors, tungsten and allopurinol, decreased MNP XOR induction, nitrotyrosine staining, inflammatory cell infiltration, and alveolar cell apoptosis. Transfer of control or allopurinol treated MNP into rat lungs confirmed a specific role for MNP XOR in promoting lung inflammation. These data indicate that XOR can contribute to lung inflammation by its expression and conversion in a highly mobile inflammatory cell population.

Immunogenicity of apoptotic cells in vivo: role of antigen load, antigen-presenting cells, and cytokines.

Apoptosis allows the clearance of unwanted cells from living tissues without causing inflammation. Processing of phagocytosed apoptotic cells yields Ags that access the cytosol and the MHC class I pathway of engulfing cells and are recognized by Ag-specific CTL. We show here that injection of apoptotic RMA cells, a syngeneic T cell lymphoma, into C57BL/6 mice results in priming of a functional and long-lasting tumor-specific immune response. Cross-priming of CTLs by apoptotic cells requires CD4+ T cell help. Apoptotic cells, however, are at least 20-fold less immunogenic than nonreplicating live cells. Immunogenicity of apoptotic cells is proportional to the number of cells injected, correlates with the serum concentration of IL-10 and IL-1beta cytokines, and is enhanced in IL-10 knockout mice. Moreover, immunization with dendritic cells (DCs), but not macrophages (Mphi), pulsed with apoptotic cells primes tumor-specific CTLs and confers protection against a tumor challenge. Our findings demonstrate that tumor cells undergoing apoptosis are, though scarcely, immunogenic in vivo, outline the different roles of Mphi and DCs in the physiologic clearance of unwanted cells, and have implications in designing immunomodulating vaccines.

The local xenogeneic graft-versus-host reaction as a clinical test for immunocompetence of human T lymphocytes.

Studies carried out in our laboratory during the years indicated that the local xenogeneic graft-versus-host reaction (GVHR) might serve as a useful clinical assay of the immunocompetence of human T lymphocytes. Additional studies were therefore carried out using purified populations of B, T and null cells as well as normal mononuclear cell populations, so as to determine the nature of the cells responsible for induction of the reaction and further delineate the factors capable of modifying this pattern of reactivity. Populations of T cells alone gave the largest reaction whereas both B cells from patients with chronic lymphatic leukemia and null cells from patients with acute lymphatic leukemia failed completely to induce a GVHR. The addition of anti-T-lymphocytic serum abolished the reaction, providing further proof of the role played by T lymphocytes. Thymic hormone (THF) was found to enhance the reaction when applied both in vivo and in vitro. The immunostimulatory agents transfer factor and levamisole also enhanced the GVHR obtained with normal mononuclear cells. Cytoxan was found to have an enhancing effect at low doses and an inhibiting effect at high doses. Trypsin also acted to abolish the GVHR. The combination of two populations of normal mononuclears always gave a larger GVHR, indicating allogeneic antigen stimulation. Depletion of the monocytes from the population of normal mononuclears resulted in a smaller reaction, providing further evidence that monocytes are required for T-lymphocyte antigen-induced reactivity. On the basis of these findings it is proposed that the local xenogeneic GVHR is a useful clinical test for the measurement of immunocompetence of T lymphocytes, for the differential diagnosis of leukemias and for the determination of the effectiveness of THF.