The role of group 1 and group 2 CD1-restricted T cells in microbial immunity

Airway Macrophage and Dendritic Cell Subsets in the Resting Human Lung

Dendritic cells (DCs) and macrophages (MΦs) are antigen-presenting phagocytic cells found in many peripheral tissues of the human body, including the blood, lymph nodes, skin, and lung. They are vital to maintaining steady-state respiration in the human lung based on their ability to clear airways while also directing tolerogenic or inflammatory responses based on specific stimuli. Over the past three decades, studies have determined that there are multiple subsets of these two general cell types that exist in the airways and interstitium. Identifying these numerous subsets has proven challenging, especially with the unique microenvironments present in the lung. Cells found in the vasculature are not the same subsets found in the skin or the lung, as demonstrated by surface marker expression. By transcriptional profiling, these subsets show similarities but also major differences. Primary human lung cells and/ or tissues are difficult to acquire, particularly in a healthy condition. Additionally, surface marker screening and transcriptional profiling are continually identifying new DC and MΦ subsets. While the overall field is moving forward, we emphasize that more attention needs to focus on replicating the steady-state microenvironment of the lung to reveal the physiological functions of these subsets.

TLR3 signaling in macrophages is indispensable for the protective immunity of invariant natural killer T cells against enterovirus 71 infection

Enterovirus 71 (EV71) is the most virulent pathogen among enteroviruses that cause hand, foot and mouth disease in children but rarely in adults. The mechanisms that determine the age-dependent susceptibility remain largely unclear. Here, we found that the paucity of invariant natural killer T (iNKT) cells together with immaturity of the immune system was related to the susceptibility of neonatal mice to EV71 infection. iNKT cells were crucial antiviral effector cells to protect young mice from EV71 infection before their adaptive immune systems were fully mature. EV71 infection led to activation of iNKT cells depending on signaling through TLR3 but not other TLRs. Surprisingly, iNKT cell activation during EV71 infection required TLR3 signaling in macrophages, but not in dendritic cells (DCs). Mechanistically, interleukin (IL)-12 and endogenous CD1d-restricted antigens were both required for full activation of iNKT cells. Furthermore, CD1d-deficiency led to dramatically increased viral loads in central nervous system and more severe disease in EV71-infected mice. Altogether, our results suggest that iNKT cells may be involved in controlling EV71 infection in children when their adaptive immune systems are not fully developed, and also imply that iNKT cells might be an intervention target for treating EV71-infected patients.

Enterovirus 71 (EV71) is a major causative pathogen of hand, foot and mouth disease. EV71 infection occurs mainly in children but rarely in adults. The factors that determine the susceptibility of children to EV71 infection remain elusive. Here, we found that the paucity of invariant natural killer T (iNKT) cells in new-born mice was associated with their susceptibility to EV71 infection. Furthermore, iNKT cells played a critical role in protecting older young mice from EV71 infection before their adaptive immune systems were fully developed. Mechanistically, TLR3 signaling in macrophages, but not in dendritic cells, was essentially required for iNKT cell activation during EV71 infection. Both interleukin (IL)-12 production and endogenous lipid antigens presented by macrophages were required for full iNKT cell activation. iNKT cells tended to prevent the dissemination of EV71 into central nervous system. Taken together, our findings provide a new insight into the susceptibility of children to EV71 infection, and imply that the manipulation of iNKT cells might represent a potential therapeutic strategy for HFMD and other viral infectious diseases in children.

Long-term treatment of Langerhans cell histiocytosis of the mandibular condyle with indomethacin

Langerhans cell histiocytosis (LCH) most commonly occurs as a localized solitary bone lesion and appears predominantly in pediatric patients. LCH is characterized by the proliferation and accumulation of Langerhans cells which may cause pain and adjacent soft-tissue swelling. This disease is of clinical importance to dental professionals because LCH commonly involves the oral and maxillofacial region and early symptoms can be manifested in the jaw and, when overlooked, may result in extensive destruction of the involved structures. Considering the fact that this is a relatively rare entity, close investigation of the cases that are encountered are warranted. Herein we report a case of LCH occurring in the left condyle of an 11-year-old boy that initially showed clinical symptoms mimicking an abscess of the temporomandibular joint. The clinical and radiographic features, differential diagnosis, treatment, and long-term follow-up of this patient with indomethacin are presented.

Mycolic acids constitute a scaffold for mycobacterial lipid antigens stimulating CD1-restricted T cells

CD1-restricted lipid-specific T lymphocytes are primed during infection with Mycobacterium tuberculosis, the causative agent of tuberculosis. Here we describe the antigenicity of glycerol monomycolate (GroMM), which stimulates CD1b-restricted CD4(+) T cell clones. Chemical characterization of this antigen showed that it exists as two stereoisomers, one synthetic isomer being more stimulatory than the other. The hydroxyl groups of glycerol and the mycolic acid length are critical for triggering the T cell responses. GroMM was presented by M. tuberculosis-infected dendritic cells, demonstrating that the antigen is available for presentation during natural infection. Ex vivo experiments showed that GroMM stimulated T cells from vaccinated or latently infected healthy donors but not cells from patients with active tuberculosis, suggesting that GroMM-specific T cells are primed during infection and their detection correlates with lack of clinical active disease.

V alpha14 i NKT cells are innate lymphocytes that participate in the immune response to diverse microbes

Natural Killer T (NKT) cells constitute a conserved T lymphocyte sublineage that has been implicated in the regulation of various immune responses, including the responses to viruses, bacteria, and parasites. NKT cells recognize self and foreign glycolipids presented by CD1d, a non-classical antigen-presenting molecule, and they rapidly produce various cytokines. Many studies have shown that NKT cells have protective roles following microbial infection through the amplification of innate and adaptive immunity, although NKT cells have detrimental roles in some cases. Recent studies have shed light on the natural antigens recognized by NKT cells and the mechanisms whereby they contribute to host defense, and they suggest that these unique T cells have evolved to jump start the immune response to microbes.

Glycolipids as immunostimulating agents

The processing and presentation of lipid antigens by antigen presenting cells (APC) is important for defense against infection, tumor immunosurveillance, and autoimmunity. CD1, a family of cell surface glycoproteins, is responsible for the binding and presentation of lipid antigens to receptors expressed on the surface of T lymphocytes. Among the several (glyco)lipids identified to cause T-cell stimulation in complex with CD1, alpha-galactosyl ceramide (alpha-GalCer) is one of the most well studied. A combination of structure-activity relationship (SAR), crystallographic studies, and discovery of new 'natural' antigens has led to greater understanding of the structural requirements for optimal natural killer T-cell activation.

CD1-restricted T cells in host defense to infectious diseases

CD1 has been clearly shown to function as a microbial recognition system for activation of T cell responses, but its importance for mammalian protective responses against infections is still uncertain. The function of the group 1 CD1 isoforms, including human CD1a, CDlb, and CDLc, seems closely linked to adaptive immunity. These CD1 molecules control the responses of T cells that are highly specific for particular lipid antigens, the best known of which are abundantly expressed by pathogenic mycobacteria such as Mycobacterium tuberculosis and Mycobacterium leprae. Studies done mainly on human circulating T cells ex vivo support a significant role for group I CD1-restricted T cells in protective immunity to mycobacteria and potentially other pathogens, although supportive data from animal models is currently limited. In contrast, group 2 CD1 molecules, which include human CD1d and its orthologs, have been predominantly associated with the activation of CD1d-restricted NKT cells, which appear to be more appropriately viewed as a facet of the innate immune system. Whereas the recognition of certain self-lipid ligands by CD d-restricted NKT cells is well accepted, the importance of these T cells in mediating adaptive immune recognition of specific microbial lipid antigens remains controversial. Despite continuing uncertainty about the role of CD 1d-restricted NKT cells in natural infections, studies in mouse models demonstrate the potential of these T cells to exert various effects on a wide spectrum of infectious diseases, most likely by serving as a bridge between innate and adaptive immune responses.

The in vivo response of invariant natural killer T cells to glycolipid antigens

Invariant natural killer T (iNKT) cells are a subset of T lymphocytes that recognizes glycolipid antigens presented by the major histocompatibility complex class I-related protein CD1d. Although iNKT cells have received a lot of attention as targets for the development of immunotherapies, few studies have investigated the in vivo response of iNKT cells to glycolipid antigen activation. Accumulating evidence indicates that iNKT cells generate a dynamic response to in vivo activation by glycolipid antigens that is characterized by surface receptor downmodulation, expansion, cytokine production, cross talk with other cells, homeostatic contraction, and acquisition of an anergic phenotype. These studies provide new insight into the biology of iNKT cells and have important implications for designing safe and effective iNKT cell-based vaccines and therapies.

Mycobacterium tuberculosis-specific CD8+ T cells and their role in immunity

There are more cases of tuberculosis in the world today than at any other time in history. The global epidemic has generated intense interest into the immunological mechanisms that control infection. Although CD4+ T cells play a critical role in host immunity to Mycobacterium tuberculosis, there is considerable interest in understanding the role of other T cell subsets in preventing disease development following infection. CD8+ T cells are required for optimum host defense following M. tuberculosis infection, which has led to investigation into how this protective effect is mediated. A critical review of recent literature regarding the role of CD8+ T cells in protective immunity to M. tuberculosis infection is now required to address the strengths and weaknesses of these studies. In this article, we evaluate the evidence that CD8+ T cells are critical in immunity to M. tuberculosis infection. We discuss the specific mycobacterial proteins that are recognized by CD8+ T cells elicited during infection. Finally, we examine the effector mechanisms of CD8+ T cells generated during infection and synthesize recent studies to consider the protective roles that these T cells serve in vivo.

CD3+ cells transfer the hypersensitive granulomatous response to mycobacterial glycolipid trehalose 6,6′-dimycolate in mice

The granulomatous response is the characteristic histological feature ofMycobacterium tuberculosisinfection that is essential for organism containment. Trehalose 6,6-dimycolate (TDM), a cell-wall glycolipid present on most mycobacterial species, has been implicated in the pathogenesis ofM. tuberculosisinfection. TDM has potent immunoregulatory and inflammatory properties, and can be used to model granulomatous reactions that mimic, in part, pathology caused during active infection. This study examined the hypersensitive granulomatous response, focusing on cellular responses specific to TDM. Lungs from mice immunized with TDM emulsion demonstrated exacerbated histological damage, inflammation, and lymphocytic infiltration upon subsequent challenge with TDM. Splenocytes recovered from these mice demonstrated significant interferon (IFN)-γproduction during recall response to TDM, as well as increased production of proinflammatory mediators (tumour necrosis factor-α, interleukin-6 and macrophage inflammatory protein-1α). The exacerbated response could be adoptively transferred to naïve mice. Administration of non-adherent lymphocytes or purified CD3+cells from TDM-immunized mice led to increased inflammation, lymphocytic infiltration, and vascular endothelial cell damage upon challenge with TDM. Recipient mice that received immunized CD3+lymphocytes demonstrated significant increases in Th1-type cytokines and proinflammatory mediators in lung tissue following TDM challenge. When CD1d−/−mice were immunized with TDM, they failed to generate a specific IFN-γresponse, suggesting a role for this molecule in the generation of hypersensitivity. These experiments provide further evidence for the involvement of TDM-specific CD3+T cells in pathological damage elicited duringM. tuberculosisinfection.

H2–M3-restricted T cell response to infection

H2-M3 is a major histocompatibility complex class Ib molecule that presents N-formylated peptides to specific CD8+ T cells. Prokaryotic, but not eukaryotic, translation begins with the addition of N-formyl methionine, suggesting a role for these H2-M3-restricted T cells in response to bacterial infection. Indeed, these cells constitute a non-redundant "early" component of anti-microbial response.

Dual functions of murine gammadelta cells in inflammation and autoimmunity in coxsackievirus B3-induced myocarditis: role of Vgamma1+ and Vgamma4+ cells

Coxsackieviruses are a cause of clinical myocarditis. Both virus replication and host defense mechanisms, including virus-induced autoimmunity, mediate heart injury and cardiac dysfunction. Vgamma4+ cells kill infected cardiocytes and virus-specific CD4+ Th2 cells through Fas-dependent apoptosis and CD1d. The CD4+ Th1 response is necessary for activation of the autoimmune CD8+ T cells, which kill uninfected cardiocytes through perforin-dependent mechanisms.