ETV3 and ETV6 enable monocyte differentiation into dendritic cells by repressing macrophage fate commitment.

In inflamed tissues, monocytes differentiate into macrophages (mo-Macs) or dendritic cells (mo-DCs). In chronic nonresolving inflammation, mo-DCs are major drivers of pathogenic events. Manipulating monocyte differentiation would therefore be an attractive therapeutic strategy. However, how the balance of mo-DC versus mo-Mac fate commitment is regulated is not clear. In the present study, we show that the transcriptional repressors ETV3 and ETV6 control human monocyte differentiation into mo-DCs. ETV3 and ETV6 inhibit interferon (IFN)-stimulated genes; however, their action on monocyte differentiation is independent of IFN signaling. Instead, we find that ETV3 and ETV6 directly repress mo-Mac development by controlling MAFB expression. Mice deficient for Etv6 in monocytes have spontaneous expression of IFN-stimulated genes, confirming that Etv6 regulates IFN responses in vivo. Furthermore, these mice have impaired mo-DC differentiation during inflammation and reduced pathology in an experimental autoimmune encephalomyelitis model. These findings provide information about the molecular control of monocyte fate decision and identify ETV6 as a therapeutic target to redirect monocyte differentiation in inflammatory disorders.

Early SIV and HIV infection promotes the LILRB2/MHC-I inhibitory axis in cDCs.

Classical dendritic cells (cDCs) play a pivotal role in the early events that tip the immune response toward persistence or viral control. In vitro studies indicate that HIV infection induces the dysregulation of cDCs through binding of the LILRB2 inhibitory receptor to its MHC-I ligands and the strength of this interaction was proposed to drive disease progression. However, the dynamics of the LILRB2/MHC-I inhibitory axis in cDCs during early immune responses against HIV are yet unknown. Here, we show that early HIV-1 infection induces a strong and simultaneous increase of LILRB2 and MHC-I expression on the surface of blood cDCs. We further characterized the early dynamics of LILRB2 and MHC-I expression by showing that SIVmac251 infection of macaques promotes coordinated up-regulation of LILRB2 and MHC-I on cDCs and monocytes/macrophages, from blood and lymph nodes. Orientation towards the LILRB2/MHC-I inhibitory axis starts from the first days of infection and is transiently induced in the entire cDC population in acute phase. Analysis of the factors involved indicates that HIV-1 replication, TLR7/8 triggering, and treatment by IL-10 or type I IFNs increase LILRB2 expression. Finally, enhancement of the LILRB2/MHC-I inhibitory axis is specific to HIV-1 and SIVmac251 infections, as expression of LILRB2 on cDCs decreased in naturally controlled chikungunya virus infection of macaques. Altogether, our data reveal a unique up-regulation of LILRB2 and its MHC-I ligands on cDCs in the early phase of SIV/HIV infection, which may account for immune dysregulation at a critical stage of the anti-viral response.

Functional specialization of short-lived and long-lived macrophage subsets in human tonsils.

Macrophages play a central role in tissue homeostasis and host defense. However, the properties of human macrophages in non-diseased tissues remain poorly understood. Here, we characterized human tonsil macrophages and identified three subsets with distinct phenotype, transcriptome, life cycle, and function. CD36hi macrophages were related to monocytes, while CD36lo macrophages showed features of embryonic origin and CD36int macrophages had a mixed profile. scRNA-seq on non-human primate tonsils showed that monocyte recruitment did not pre-exist an immune challenge. Functionally, CD36hi macrophages were specialized for stimulating T follicular helper cells, by producing Activin A. Combining reconstruction of ligand-receptor interactions and functional assays, we identified stromal cell-derived TNF-α as an inducer of Activin A secretion. However, only CD36hi macrophages were primed for Activin A expression, via the activity of IRF1. Our results provide insight into the heterogeneity of human lymphoid organ macrophages and show that tonsil CD36hi macrophage specialization is the result of both intrinsic features and interaction with stromal cells.

Identification of Antigen Presenting Cell Subsets Supporting Human Tfh Differentiation.

CD4+ T follicular helper (Tfh) cells are essential for initiating and regulating efficient humoral responses in secondary lymphoid organs. Tfh polarization and differentiation is driven by multiple stimuli delivered by antigen presenting cells (APCs). APCs represent a complex population of immune cells, comprising several subpopulations (dendritic cells and macrophages) that are distinguished by their phenotype, ontogeny, and functions. In order to better identify and understand the role of the different APC subsets in human Tfh biology, we have used in vitro assays based on the co-culture of APCs and T cells. This chapter describes two complementary protocols. The first protocol describes an assay to study the capacity of APCs to drive Tfh polarization from naive CD4+ T cells. The second protocol is designed to address the role of APCs in modulating effector functions of mature Tfh cells.

Mass Cytometry Analysis Reveals Complex Cell-State Modifications of Blood Myeloid Cells During HIV Infection.

Dendritic cells (DC), which are involved in orchestrating early immune responses against pathogens, are dysregulated in their function by HIV infection. This dysregulation likely contributes to tip the balance toward viral persistence. Different DC subpopulations, including classical (cDCs) and plasmacytoid (pDCs) dendritic cells, are subjected to concomitant inflammatory and immunoregulatory events during HIV infection, which hampers the precise characterization of their regulation through classical approaches. Here, we carried out mass cytometry analysis of blood samples from early HIV-infected patients that were longitudinally collected before and after 1 year of effective combination antiretroviral therapy (cART). Blood samples from HIV controller patients who naturally control the infection were also included. Our data revealed that plasma HIV RNA level was positively associated with a loss of cDC and pDC subpopulations that display high expression of LILR immunomodulatory receptors. Conversely, specific monocyte populations co-expressing high levels of HLA-I, 3 immunomodulatory receptors, CD64, LILRA2, and LILRB4, and the restriction factor CD317 (also known as BST2/Tetherin), were more abundant in early HIV-infection. Finally, our analysis revealed that the blood of HIV controller patients contained in a higher abundance a particular subtype of CD1c+ cDCs, characterized by elevated co-expression of CD32b inhibitory receptor and HLA-DR antigen-presentation molecules. Overall, this study unravels the modifications induced in DC and monocyte subpopulations in different HIV+ conditions, and provides a better comprehension of the immune regulation/dysregulation mechanisms induced during this viral infection.

Mass Cytometry Analysis Reveals the Landscape and Dynamics of CD32a+ CD4+ T Cells From Early HIV Infection to Effective cART.

CD32a has been proposed as a specific marker of latently HIV-infected CD4+ T cells. However, CD32a was recently found to be expressed on CD4+ T cells of healthy donors, leading to controversy on the relevance of this marker in HIV persistence. Here, we used mass cytometry to characterize the landscape and variation in the abundance of CD32a+ CD4+ T cells during HIV infection. To this end, we analyzed CD32a+ CD4+ T cells in primary HIV infection before and after effective combination antiretroviral therapy (cART) and in healthy donors. We found that CD32a+ CD4+ T cells include heterogeneous subsets that are differentially affected by HIV infection. Our analysis revealed that naive (N), central memory (CM), and effector/memory (Eff/Mem) CD32a+ CD4+ T-cell clusters that co-express LILRA2- and CD64-activating receptors were more abundant in primary HIV infection and cART stages. Conversely, LILRA2- CD32a+ CD4+ T-cell clusters of either the TN, TCM, or TEff/Mem phenotype were more abundant in healthy individuals. Finally, an activated CD32a+ CD4+ TEff/Mem cell cluster co-expressing LILRA2, CD57, and NKG2C was more abundant in all HIV stages, particularly during primary HIV infection. Overall, our data show that multiple abundance modifications of CD32a+ CD4+ T-cell subsets occur in the early phase of HIV infection, and some of which are conserved after effective cART. Our study brings a better comprehension of the relationship between CD32a expression and CD4+ T cells during HIV infection.