Ubiquitous versus restricted expression of the two mouse dendritic cell C-type lectin receptors, DCIR1 and DCAR2, among myeloid cells

The C-type lectin DCIR contributes to the immune response and pathogenesis of colorectal cancer

Development and progression of malignancies are accompanied and influenced by alterations in the surrounding immune microenvironment. Understanding the cellular and molecular interactions between immune cells and cancer cells has not only provided important fundamental insights into the disease, but has also led to the development of new immunotherapies. The C-type lectin Dendritic Cell ImmunoReceptor (DCIR) is primarily expressed by myeloid cells and is an important regulator of immune homeostasis, as demonstrated in various autoimmune, infectious and inflammatory contexts. Yet, the impact of DCIR on cancer development remains largely unknown. Analysis of available transcriptomic data of colorectal cancer (CRC) patients revealed that high DCIR gene expression is associated with improved patients' survival, immunologically "hot" tumors and high immunologic constant of rejection, thus arguing for a protective and immunoregulatory role of DCIR in CRC. In line with these correlative data, we found that deficiency of DCIR1, the murine homologue of human DCIR, leads to the development of significantly larger tumors in an orthotopic murine model of CRC. This phenotype is accompanied by an altered phenotype of tumor-associated macrophages (TAMs) and a reduction in the percentage of activated effector CD4+ and CD8+ T cells in CRC tumors of DCIR1-deficient mice. Overall, our results show that DCIR promotes antitumor immunity in CRC, making it an attractive target for the future development of immunotherapies to fight the second deadliest cancer in the world.

C-type lectin receptor CLEC4A2 promotes tissue adaptation of macrophages and protects against atherosclerosis

Macrophages are integral to the pathogenesis of atherosclerosis, but the contribution of distinct macrophage subsets to disease remains poorly defined. Using single cell technologies and conditional ablation via a LysM^Cre+Clec4a2^flox/DTR mouse strain, we demonstrate that the expression of the C-type lectin receptor CLEC4A2 is a distinguishing feature of vascular resident macrophages endowed with athero-protective properties. Through genetic deletion and competitive bone marrow chimera experiments, we identify CLEC4A2 as an intrinsic regulator of macrophage tissue adaptation by promoting a bias in monocyte-to-macrophage in situ differentiation towards colony stimulating factor 1 (CSF1) in vascular health and disease. During atherogenesis, CLEC4A2 deficiency results in loss of resident vascular macrophages and their homeostatic properties causing dysfunctional cholesterol metabolism and enhanced toll-like receptor triggering, exacerbating disease. Our study demonstrates that CLEC4A2 licenses monocytes to join the vascular resident macrophage pool, and that CLEC4A2-mediated macrophage homeostasis is critical to combat cardiovascular disease.

The contribution of distinct subsets of macrophages to atherosclerosis is poorly understood. Here the authors describe a protective subset of vascular macrophages expressing the C-type lectin receptor CLEC4A2, which licenses monocytes to join the resident vascular macrophage pool and ensures vascular homeostasis.

Recognition of Mycobacteria by Dendritic Cell Immunoactivating Receptor

Mycobacteria have unique lipids on their cell walls, and the structures and physiological activities of these lipid components have been the subject of many studies. Although the host receptors for mycobacterial lipid have long been elusive, in recent years C-type lectin receptors (CLRs) have been reported to recognize these components. The dendritic cell immunoactivating receptor (DCAR), a CLR member, is encoded by Clec4b1. DCAR, which was identified in 2003, is reported to be associated with the immunoreceptor tyrosine-based activation motif (ITAM)-containing adaptor protein, the Fc receptor γ chain (FcRγ). However, its physiological ligand and biological function were unknown. We recently identified DCAR as an activating receptor for mycobacteria. DCAR recognizes acylated phosphatidyl-inositol mannosides (PIMs) in mycobacteria to promote Th1 responses during mycobacterial infection. This review summarizes recent discoveries about the ligands and immunological roles of DCAR.