Lea Brys

Tolerance and M2 (alternative) macrophage polarization are related processes orchestrated by p50 nuclear factor κB

Cells of the monocyte–macrophage lineage play a central role in the orchestration and resolution of inflammation. Plasticity is a hallmark of mononuclear phagocytes, and in response to environmental signals these cells undergo different forms of polarized activation, the extremes of which are called classic or M1 and alternative or M2. NF-κB is a key regulator of inflammation and resolution, and its activation is subject to multiple levels of regulation, including inhibitory, which finely tune macrophage functions. Here we identify the p50 subunit of NF-κB as a key regulator of M2-driven inflammatory reactions in vitro and in vivo. p50 NF-κB inhibits NF-κB–driven, M1-polarizing, IFN-β production. Accordingly, p50-deficient mice show exacerbated M1-driven inflammation and defective capacity to mount allergy and helminth-driven M2-polarized inflammatory reactions. Thus, NF-κB p50 is a key component in the orchestration of M2-driven inflammatory reactions.

Macrophage galactose-type C-type lectins as novel markers for alternatively activated macrophages elicited by parasitic infections and allergic airway inflammation

Molecular markers, especially surface markers associated with type II, cytokine‐dependent, alternatively activated macrophages (aaMF), remain scarce. Besides the earlier documented markers, macrophage mannose receptor and arginase 1, we demonstrated recently that murine aaMF are characterized by increased expression of found in inflammatory zone 1 (FIZZ1) and the secretory lectin Ym. We now document that expression of the two members of the mouse macrophage galactose‐type C‐type lectin gene family (mMGL1 and mMGL2) is induced in diverse populations of aaMF, including peritoneal macrophages elicited during infection with the protozoan Trypanosoma brucei brucei or the Helminth Taenia crassiceps and alveolar macrophages elicited in a mouse model of allergic asthma. In addition, we demonstrate that in vitro, interleukin‐4 (IL‐4) and IL‐13 up‐regulate mMGL1 and mMGL2 expression and that in vivo, induction of mMGL1 and mMGL2 is dependent on IL‐4 receptor signaling. Moreover, we show that expression of MGL on human monocytes is also up‐regulated by IL‐4. Hence, macrophage galactose‐type C‐type lectins represent novel surface markers for murine and human aaMF.

Reactive Oxygen Species and 12/15-Lipoxygenase Contribute to the Antiproliferative Capacity of Alternatively Activated Myeloid Cells Elicited during Helminth Infection

Understanding the role of CD11b+GR-1+ myeloid suppressor cells in the immune suppression and immunoregulation associated with a variety of diseases may provide therapeutic opportunities. In this article, we show, in a model of helminth infection, that CD11b+GR-1+ myeloid suppressor cells but not CD11b+F4/80high mature macrophages expanded in the peritoneal cavity of BALB/c mice implanted with Taenia crassiceps. Peritoneal cell populations from early stage-infected animals impaired T cell proliferation by secreting NO. Yet, they lost their ability to secrete NO in the late stage of infection. Concomitantly, their capacity to exert arginase activity and to express mRNAs coding for FIZZ1 (found in inflammatory zone 1), Ym, and macrophage galactose-type C-type lectin increased. Furthermore, cells from early stage-infected mice triggered T cells to secrete IFN-γ and IL-4, whereas in the late stage of infection, they only induced IL-4 production. These data suggest that CD11b+GR-1+ myeloid suppressor cells displaying an alternative activation phenotype emerged gradually as T. crassiceps infection progressed. Corroborating the alternative activation status in the late stage of infection, the suppressive activity relied on arginase activity, which facilitated the production of reactive oxygen species including H2O2 and superoxide. We also document that the suppressive activity of alternative myeloid suppressor cells depended on 12/15-lipoxygenase activation generating lipid mediators, which triggered peroxisome proliferator-activated receptor-γ. IL-4 and IL-13 signaling contributed to the expansion of myeloid suppressor cells in the peritoneal cavity of T. crassiceps-infected animals and to their antiproliferative activity by allowing arginase and 12/15-lipoxygenase gene expression.

Relative Contribution of Interferon-γ and Interleukin-10 to Resistance to Murine African Trypanosomosis

Resistance to Trypanosoma brucei brucei has been correlated with the ability of infected animals to produce interferon (IFN)-gamma and tumor necrosis factor (TNF) in an early phase of infection, followed by interleukin (IL)-4 and IL-10 in late and chronic stages of the disease. Contributions of IFN-gamma and IL-10 in the control of parasitemia and survival of mice infected with T. brucei brucei were investigated by using IFN-gamma(-/-) and IL-10(-/-) mice. Results suggest that IFN-gamma, mainly secreted by CD8(+) T cells, is essential for parasite control via macrophage activation, which results in TNF and nitric oxide secretions. IL-10, partially secreted by CD4(+) T cells, seems to be important for the survival of infected mice. Its absence resulted in the sustained secretion of inflammatory mediators, which indicated the role of IL-10 in maintaining the balance between pathogenic and protective immune responses during African trypanosomosis.

IL-10 Dampens TNF/Inducible Nitric Oxide Synthase-Producing Dendritic Cell-Mediated Pathogenicity during Parasitic Infection

Antiparasite responses are associated with the recruitment of monocytes that differentiate to macrophages and dendritic cells at the site of infection. Although classically activated monocytic cells are assumed to be the major source of TNF and NO during Trypanosoma brucei brucei infection, their cellular origin remains unclear. In this study, we show that bone marrow-derived monocytes accumulate and differentiate to TNF/inducible NO synthase-producing dendritic cells (TIP-DCs) in the spleen, liver, and lymph nodes of T. brucei brucei-infected mice. Although TIP-DCs have been shown to play a beneficial role in the elimination of several intracellular pathogens, we report that TIP-DCs, as a major source of TNF and NO in inflamed organs, could contribute actively to tissue damage during the chronic stage of T. brucei brucei infection. In addition, the absence of IL-10 leads to enhanced differentiation of monocytes to TIP-DCs, resulting in exacerbated pathogenicity and early death of the host. Finally, we demonstrate that sustained production of IL-10 following IL-10 gene delivery treatment with an adeno-associated viral vector to chronically infected mice limits the differentiation of monocytes to TIP-DCs and protects the host from tissue damage.

Nitric Oxide-Independent CTL Suppression during Tumor Progression: Association with Arginase-Producing (M2) Myeloid Cells

Most of the mice bearing a s.c. BW-Sp3 lymphoma tumor mount a CD8+ T cell-mediated response resulting in tumor regression. Nonetheless, tumor progression occurs in some of the recipients and is associated with CTL inactivity. We demonstrated that T cell-activating APC were induced in regressors whereas T cell suppressive myeloid cells predominated in the spleen of progressors. Indeed, in vitro depletion of either the adherent or the CD11b+ populations restored T cell cytotoxicity and proliferation in these mice. This CTL inhibition was cell-to-cell contact-dependent but not mediated by NO. However, the same progressor suppressive cells prevented the activity of in vitro-restimulated CTLs derived from regressors in a cell-to-cell contact and NO-dependent fashion. Thus, either the NO-dependent or -independent suppressive pathway prevailed, depending on the target CTL population. In addition, the suppressive population expressed a high arginase activity, suggesting an association of the suppressive phenotype with alternatively activated (M2) myeloid cells. However, the high arginase activity is not directly involved in the suppressive process. Our results provide new insights for myeloid cell-mediated CTL inhibition during cancer progression.

Hemozoin is a key factor in the induction of malaria-associated immunosuppression

Infection‐associated immunoincompetence during malaria might result from macrophage dysfunction. In the present study, we investigated the role of macrophages as target for immunosuppression during infection, using the murine Plasmodium c. chabaudi model. Special attention has been paid to the analysis of processing/presentation of protein antigens and presentation of peptides, using cocultures of peritoneal exudate cells (PECs) from infected mice and antigen‐specific T‐cell hybridomas. The results obtained indicate a defective processing of protein antigens that becomes maximal at acute parasitemias. In addition, macrophages from acutely infected mice suppress the interleukin‐2 production by the antigen‐activated T‐cell hybridomas. This effect was independent of prostaglandin and nitric oxide production by the macrophage. The possible role of parasite components in the impaired accessory cell function of PECs was investigated and hemozoin, the end‐product of the hemoglobin catabolism by intraerythrocytic malaria parasites, was found to induce similar infection‐associated deficiencies in vitro. Moreover, hemozoin, was shown to mimic the immunosuppressive effects induced in PECs during in‐vivo infections with P. chabaudi. In conclusion, we propose that hemozoin is a key factor in the malaria‐associated immunosuppression, affecting both the antigen processing and immunomodulatory functions of macrophages.

Alternatively Activated Myeloid Cells Limit Pathogenicity Associated with African Trypanosomiasis through the IL-10 Inducible Gene Selenoprotein P

Uncontrolled inflammation is a major cause of tissue injury/pathogenicity often resulting in death of a host infected with African trypanosomes. Thus, comparing the immune response in hosts that develop different degrees of disease severity represents a promising approach to discover processes contributing to trypanosomiasis control. It is known that limitation of pathogenicity requires a transition in the course of infection, from an IFN-γ-dependent response resulting in the development of classically activated myeloid cells (M1), to a counterbalancing IL-10-dependent response associated with alternatively activated myeloid cells (M2). Herein, mechanisms and downstream effectors by which M2 contribute to lower the pathogenicity and the associated susceptibility to African trypanosomiasis have been explored. Gene expression analysis in IL-10 knockout and wild-type mice, that are susceptible and relatively resistant to Trypanosoma congolense infection, respectively, revealed a number of IL-10-inducible genes expressed by M2, including Sepp1 coding for selenoprotein P. Functional analyses confirm that selenoprotein P contributes to limit disease severity through anti-oxidant activity. Indeed, Sepp1 knockout mice, but not Sepp1Δ240-361 mice retaining the anti-oxidant motif but lacking the selenium transporter domain of selenoprotein P, exhibited increased tissue injury that associated with increased production of reactive oxygen species and increased apoptosis in the liver immune cells, reduced parasite clearance capacity of myeloid cells, and decreased survival. These data validate M2-associated molecules as functioning in reducing the impact of parasite infection on the host.

African Trypanosomiasis: Naturally Occurring Regulatory T Cells Favor Trypanotolerance by Limiting Pathology Associated with Sustained Type 1 Inflammation

Tolerance to African trypanosomes requires the production of IFN-γ in the early stage of infection that triggers the development of classically activated macrophages controlling parasite growth. However, once the first peak of parasitemia has been controlled, down-regulation of the type 1 immune response has been described. In this study, we have evaluated whether regulatory T cells (Tregs) contribute to the limitation of the immune response occurring during Trypanosoma congolense infection and hereby influence the outcome of the disease in trypanotolerant C57BL/6 host. Our data show that Foxp3+ Tregs originating from the naturally occurring Treg pool expanded in the spleen and the liver of infected mice. These cells produced IL-10 and limited the production of IFN-γ by CD4+ and CD8+ effector T cells. Tregs also down-regulated classical activation of macrophages resulting in reduced TNF-α production. The Treg-mediated suppression of the type 1 inflammatory immune response did not hamper parasite clearance, but was beneficial for the host survival by limiting the tissue damages, including liver injury. Collectively, these data suggest a cardinal role for naturally occurring Tregs in the development of a trypanotolerant phenotype during African trypanosomiasis.

Identification of a cytolytic protein in the coelomic fluid of Eisenia foetida earthworms

Total coelomic fluid of earthworms Eisenia foetida (Oligochaeta, Annelida) is capable of lysing different mammalian tumor cell lines. This cytolytic activity is different from tumor necrosis factor (TNF)-mediated lysis and is not due to proteolysis. Total coelomic fluid was subjected to ion-exchange chromatography separation and a fraction with prominent cytolytic activity was used to elicit monoclonal antibodies that were screened for their capacity to neutralize the cytolytic effect of total coelomic fluid. One of the prepared neutralizing IgG antibodies was used for the immunoaffinity purification of a cytolytic factor from total coelomic fluid. SDS-PAGE and Western blot analyses revealed a protein band with an apparent molecular weight of 42 kDa. This cytolytic protein (termed CCF-1 or coelomic cytolytic factor 1) can be adsorbed on the surface of opsonized particles and may be involved in opsonizing and hemolytic effects of coelomic fluid.