Abundant data link hypercholesterolaemia to atherogenesis. However, only recently have we appreciated that inflammatory mechanisms couple dyslipidaemia to atheroma formation. Leukocyte recruitment and expression of pro-inflammatory cytokines characterize early atherogenesis, and malfunction of inflammatory mediators mutes atheroma formation in mice. Moreover, inflammatory pathways promote thrombosis, a late and dreaded complication of atherosclerosis responsible for myocardial infarctions and most strokes. The new appreciation of the role of inflammation in atherosclerosis provides a mechanistic framework for understanding the clinical benefits of lipid-lowering therapies. Identifying the triggers for inflammation and unravelling the details of inflammatory pathways may eventually furnish new therapeutic targets.

Inflammation in atherosclerosis

The discovery of Toll-like receptors (TLRs) as components that recognize conserved structures in pathogens has greatly advanced understanding of how the body senses pathogen invasion, triggers innate immune responses and primes antigen-specific adaptive immunity. Although TLRs are critical for host defense, it has become apparent that loss of negative regulation of TLR signaling, as well as recognition of self molecules by TLRs, are strongly associated with the pathogenesis of inflammatory and autoimmune diseases. Furthermore, it is now clear that the interaction between TLRs and recently identified cytosolic innate immune sensors is crucial for mounting effective immune responses. Here we describe the recent advances that have been made by research into the role of TLR biology in host defense and disease.

/pdf/the-role-of-pattern-recognition-receptors-in-innate-immunity-39y77tlxza.pdf

The role of pattern-recognition receptors in innate immunity: update on Toll-like receptors

Macrophages display remarkable plasticity and can change their physiology in response to environmental cues. These changes can give rise to different populations of cells with distinct functions. In this Review we suggest a new grouping of macrophage populations based on three different homeostatic activities - host defence, wound healing and immune regulation. We propose that similarly to primary colours, these three basic macrophage populations can blend into various other 'shades' of activation. We characterize each population and provide examples of macrophages from specific disease states that have the characteristics of one or more of these populations.

/pdf/exploring-the-full-spectrum-of-macrophage-activation-b5rnrcgcen.pdf

Exploring the full spectrum of macrophage activation.

Interleukin-10 (IL-10), first recognized for its ability to inhibit activation and effector function of T cells, monocytes, and macrophages, is a multifunctional cytokine with diverse effects on most hemopoietic cell types. The principal routine function of IL-10 appears to be to limit and ultimately terminate inflammatory responses. In addition to these activities, IL-10 regulates growth and/or differentiation of B cells, NK cells, cytotoxic and helper T cells, mast cells, granulocytes, dendritic cells, keratinocytes, and endothelial cells. IL-10 plays a key role in differentiation and function of a newly appreciated type of T cell, the T regulatory cell, which may figure prominently in control of immune responses and tolerance in vivo. Uniquely among hemopoietic cytokines, IL-10 has closely related homologs in several virus genomes, which testify to its crucial role in regulating immune and inflammatory responses. This review highlights findings that have advanced our understanding of IL-10 and its receptor, as well as its in vivo function in health and disease.

Interleukin-10 and the interleukin-10 receptor.

https://www.cell.com/trends/immunology/pdf/S1471-4906(04)00295-9.pdf

The chemokine system in diverse forms of macrophage activation and polarization.

Objective: NR4A orphan receptors have been well studied in vascular and myeloid cells where they play important roles in the regulation of inflammation in atherosclerosis. NR4A1 (nerve growth facto...

NR4A1 Deletion in Marginal Zone B Cells Exacerbates Atherosclerosis in Mice-Brief Report.

A new study finds that local homeostatic expansion of conventional dendritic cells in the spleen is regulated by Fms-related tyrosine kinase-3 ligand.

Homeostasis of dendritic cell pool in lymphoid organs.

The mammalian immune system both suppresses and tolerates tumors, so understanding this complexity should benefit the development of cancer therapies. Macrophages are proposed to play an important role in suppressing the immune response to cancer cells, but it is not clear where these immune cells come from or whether there are distinct populations of macrophages with specific roles in this setting. On page 921 of this issue, Franklin et al. ( 1 ) forge a more coherent view of macrophages that are associated with tumor growth by assessing their origin, phenotype, and functions in an animal model of breast cancer.

https://science.sciencemag.org/content/sci/344/6186/801.full.pdf

Identifying the infiltrators

Originally implicated in axon guidance, semaphorins represent a large family of molecules that are now known to be expressed in the immune system. Among different semaphorins tested by reverse transcriptase-polymerase chain reaction in human immune cells, the expression of class 6 transmembrane semaphorin SEMA6A was restricted to dendritic cells (DCs). Using in-house generated monoclonal antibodies, SEMA6A expression appeared further restricted to Langerhans cells (LCs). In vivo, SEMA6A mRNA was expressed in freshly isolated skin LCs but SEMA6A protein was not detectable on normal skin and tonsillar epithelium. Of interest, SEMA6A protein was strongly expressed on skin and bone LCs and on LCs in draining lymph nodes from patients with LC histiocytosis or dermatopathic lymphadenitis, respectively, representing two inflammatory conditions in which LCs display an immature DC-LAMPlow, CD83low, and CCR7+ phenotype. SEMA6A expression was low in resting LCs generated in vitro and was enhanced by interferon (IFN)-γ but not by interleukin-4, interleukin-10, IFN-α/β, or lipopolysaccharide. Most IFN-γ-induced SEMA6A-positive cells remained immature with low CD83 and DC-LAMP/CD208 expression, but they expressed CCR7 and responded to macrophage inflammatory protein-3β (MIP-3β/CCL19). The expression of SEMA6A, for which the ligand and function remain unknown, may therefore identify an alternative IFN-γ-dependent activation status of LCs in vivo.

/pdf/the-class-6-semaphorin-sema6a-is-induced-by-interferon-g-and-3ccxbt7c7u.pdf

Frederic Geissmann

Papers

NR4A1 Deletion in Marginal Zone B Cells Exacerbates Atherosclerosis in Mice-Brief Report.

Homeostasis of dendritic cell pool in lymphoid organs.

Identifying the infiltrators

The Class 6 Semaphorin SEMA6A Is Induced by Interferon-γ and Defines an Activation Status of Langerhans Cells Observed in Pathological Situations

Disseminated toxoplasmosis following autologous bone marrow transplantation.