[Show abstract][Hide abstract] ABSTRACT: The differentiation of monocytes into dendritic cells (DC) is a key mechanism by which the innate immune system instructs the adaptive T cell response. In this study, we investigated whether leukocyte Ig-like receptor A2 (LILRA2) regulates DC differentiation by using leprosy as a model. LILRA2 protein expression was increased in the lesions of the progressive, lepromatous form vs the self-limited, tuberculoid form of leprosy. Double immunolabeling revealed LILRA2 expression on CD14+, CD68+ monocytes/macrophages. Activation of LILRA2 on peripheral blood monocytes impaired GM-CSF induced differentiation into immature DC, as evidenced by reduced expression of DC markers (MHC class II, CD1b, CD40, and CD206), but not macrophage markers (CD209 and CD14). Furthermore, LILRA2 activation abrogated Ag presentation to both CD1b- and MHC class II-restricted, Mycobacterium leprae-reactive T cells derived from leprosy patients, while cytokine profiles of LILRA2-activated monocytes demonstrated an increase in TNF-alpha, IL-6, IL-8, IL-12, and IL-10, but little effect on TGF-beta. Therefore, LILRA2 activation, by altering GM-CSF-induced monocyte differentiation into immature DC, provides a mechanism for down-regulating the ability of the innate immune system to activate the adaptive T cell response while promoting an inflammatory response.
The Journal of Immunology 01/2008; 179(12):8128-36. · 5.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: IL-1R activation is required for neutrophil recruitment in an effective innate immune response against Staphylococcus aureus infection. In this study, we investigated the mechanism of IL-1R activation in vivo in a model of S. aureus infection. In response to a S. aureus cutaneous challenge, mice deficient in IL-1beta, IL-1alpha/IL-1beta, but not IL-1alpha, developed larger lesions with higher bacterial counts and had decreased neutrophil recruitment compared with wild-type mice. Neutrophil recruitment and bacterial clearance required IL-1beta expression by bone marrow (BM)-derived cells and not by non-BM-derived resident cells. In addition, mice deficient in the inflammasome component apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) had the same defects in neutrophil recruitment and host defense as IL-1beta-deficient mice, demonstrating an essential role for the inflammasome in mediating the production of active IL-1beta to promote neutrophil recruitment in host defense against S. aureus. This finding was further supported by the ability of recombinant active IL-1beta to control the infection and promote bacterial clearance in IL-1beta-deficient mice. These studies define a key host defense circuit where inflammasome-mediated IL-1beta production by BM-derived cells signals IL-1R on non-BM-derived resident cells to activate neutrophil recruitment in the innate immune response against S. aureus in vivo.
The Journal of Immunology 12/2007; 179(10):6933-42. · 5.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Defensin is a generic name reserved for an endogenously synthesized antimicrobial agent. The purpose of this review is to describe a series of discoveries that led to the proposal that 25-hydroxylated metabolites of vitamin D are key, intracellular regulators of the synthesis and action of naturally occurring defensin molecules against bacterial antigens. The discussion will (1) highlight the basic elements of human immune response that is responsive to vitamin D, (2) recount work relevant to the extrarenal expression of the vitamin D-1-hydroxlase (CYP27b1) in the macrophage as an initiator of the innate immune response, and (3) describe recent work on the relevance of the vitamin D intracrine-autocrine-paracrine system in a model of a common and devastating human disease, tuberculosis.
Annals of the New York Academy of Sciences 12/2007; 1117:94-105. · 4.38 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Distinct CD4(+) T-cell epitopes within the same protein can be optimally processed and loaded into major histocompatibility complex (MHC) class II molecules in disparate endosomal compartments. The CD1 protein isoforms traffic to these same endosomal compartments as directed by unique cytoplasmic tail sequences, therefore we reasoned that antigen/CD1 chimeras containing the different CD1 cytoplasmic tail sequences could optimally target antigens to the MHC class II antigen presentation pathway. Evaluation of trafficking patterns revealed that all four human CD1-derived targeting sequences delivered antigen to the MHC class II antigen presentation pathway, to early/recycling, early/sorting and late endosomes/lysosomes. There was a preferential requirement for different CD1 targeting sequences for the optimal presentation of an MHC class II epitope in the following hierarchy: CD1b > CD1d = CD1c > > > CD1a or untargeted antigen. Therefore, the substitution of the CD1 ectodomain with heterologous proteins results in their traffic to distinct intracellular locations that intersect with MHC class II and this differential distribution leads to specific functional outcomes with respect to MHC class II antigen presentation. These findings may have implications in designing DNA vaccines, providing a greater variety of tools to generate T-cell responses against microbial pathogens or tumours.
[Show abstract][Hide abstract] ABSTRACT: Host defense against intracellular pathogens depends upon innate and adaptive antimicrobial effector pathways. TLR2/1-activation of monocytes leads to the vitamin D-dependent production of cathelicidin and, at the same time, an antimicrobial activity against intracellular Mycobacterium tuberculosis. To determine whether induction of cathelicidin was required for the vitamin D-triggered antimicrobial activity, the human monocytic cell line THP-1 was infected with M. tuberculosis H37Ra and then activated with the active vitamin D hormone 1,25-dihydroxyvitamin D(3) (1,25D(3)). 1,25D(3) stimulation resulted in antimicrobial activity against intracellular M. tuberculosis and expression of cathelicidin mRNA and protein. Using small interfering RNA (siRNA) specific for cathelicidin, 1,25D(3)-induced cathelicidin mRNA and protein expressions were efficiently knocked down, whereas a nonspecific siRNA control had little effect. Finally, 1,25D(3)-induced antimicrobial activity was completely inhibited in the presence of siRNA against cathelicidin, instead leading to enhanced intracellular growth of mycobacteria. These data demonstrate that cathelicidin is required for the 1,25D(3)-triggered antimicrobial activity against intracellular M. tuberculosis.
The Journal of Immunology 09/2007; 179(4):2060-3. · 5.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Toll-like receptors (TLRs) are important pattern-recognition receptors involved in host defense against a variety of pathogenic microorganisms. Activation of TLRs leads to the production of cytokines, chemokines, antimicrobial peptides, and upregulation costimulatory and adhesion molecules involved in innate and adaptive immune responses. TLRs are expressed on a variety of cell types found in the skin, including keratinocytes and Langerhans cells in the epidermis, resident and trafficking immunesystem cells such as macrophages, dendritic cells, T and B cells, and mast cells in the dermis, endothelial cells of the skin microvasculature, and skin stromal cells such as fibroblasts and adipocytes. There have been an increasing number of reports demonstrating that TLRs play a key role in cutaneous host defense mechanisms against bacterial, fungal, and viral pathogens. In addition, TLRs have also been implicated in the pathophysiology of various inflammatory skin diseases.
Seminars in Immunopathology 05/2007; 29(1):15-26. · 5.38 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Dr Robert Modlin was interviewed by Emma Quigley (Senior Editor, Expert Opinion) on 5th February 2007.
Robert L Modlin, MD, is Professor in the Division of Dermatology and in the Department of Microbiology, Immunology and Molecular Genetics at the University of California, Los Angeles. He is also the Chief of the Division of Dermatology. He completed his undergraduate studies at Johns Hopkins University and received his medical degree at the New York University School of Medicine. Dr Modlin’s interest in leprosy began during his dermatology residency at the Los Angeles County/University of Southern California Medical Center. He has studied leprosy as a model to learn about mechanisms of host defence in humans. As such, Dr Modlin’s laboratory has made fundamental insights into T cell subsets, cytokine patterns, antigen presentation, innate immunity and antimicrobial mechanisms in the human immune response to infection. He has been awarded three patents for this research. Dr Modlin has published > 150 articles, including 12 papers in Science and Nature, 4 in Nature Medicine, received the Montagna Award for outstanding young investigator from the Society for Investigative Dermatology, a merit award from the National Institutes of Health and the Sulzberger lectureship of the American Academy of Dermatology. Dr Modlin is a member of the American Society of Clinical Investigation and the American Association of Physicians. He is the Deputy Editor for the Journal of Immunology, having served on the editorial board of the Journal of Clinical Investigation, Infection and Immunity and Immunology. Dr Modlin has served on the Society for Investigative Dermatology Board of Directors.
[Show abstract][Hide abstract] ABSTRACT: The innate immune system provides the host with an immediate and rapid defense against invading microbes. Detection of foreign invaders is mediated by a class of receptors that are known as the pattern recognition receptors, such as the family of Toll-like receptors (TLRs). In humans, ten functional TLRs have been identified and they respond to conserved pathogen-associated molecular patterns derived from bacteria, mycoplasma, fungi and viruses. TLR activation leads to direct antimicrobial activity against both intracellular and extracellular bacteria, and induces an antiviral gene program. Recently, it was reported that TLR2 activation leads to the use of vitamin D3 as a mechanism to combat Mycobacterium tuberculosis. Here, we focus on recent findings concerning the TLR-induced antimicrobial mechanisms in humans and the therapeutic implications of these findings. Owing to their capability to combat a wide array of pathogens, TLRs are attractive therapeutic targets. However, additional knowledge about their antimicrobial mechanisms is needed.
Trends in Molecular Medicine 04/2007; 13(3):117-24. · 9.57 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Human infection with Mycobacterium leprae, an intracellular bacterium, presents as a clinical and immunological spectrum; thus leprosy provides an opportunity to investigate mechanisms of T-cell responsiveness to a microbial pathogen. Analysis of the T-cell receptor (TCR) repertoire in leprosy lesions revealed that TCR BV6(+) T cells containing a conserved CDR3 motif are over-represented in lesions from patients with the localized form of the disease. Here, we derived a T-cell clone from a leprosy lesion that expressed TCR BV6 and the conserved CDR3 sequence L-S-G. This T-cell clone produced a T helper type 1 cytokine pattern, directly lysed M. leprae-pulsed antigen-presenting cells by the granule exocytosis pathway, and expressed the antimicrobial protein granulysin. BV6(+) T cells may therefore functionally contribute to the cell-mediated immune response against M. leprae.
[Show abstract][Hide abstract] ABSTRACT: Although ectopic expression of 25-hydroxyvitamin D(3)-1alpha-hydroxylase (1alpha-OHase) has been recognized for many years, the precise function of this enzyme outside the kidney remains open to debate. Three specific aspects of extra-renal 1alpha-OHase have attracted most attention: (i) expression and regulation in non-classical tissues during normal physiology; (ii) effects on the immune system and inflammatory disease; (iii) expression and function in tumors. The most well-recognized manifestation of extra-renal 1alpha-OHase activity remains that found in some patients with granulomatous diseases where locally synthesized 1alpha,25(OH)(2)D(3) has the potential to spill-over into the general circulation. However, immunohistochemistry and mRNA analyses suggest that 1alpha-OHase is also expressed by a variety of normal human tissues including the gastrointestinal tract, skin, vasculature and placenta. This has promoted the idea that autocrine/paracrine synthesis of 1,25(OH)(2)D(3) contributes to normal physiology, particularly in mediating the potent effects of vitamin D on innate (macrophage) and acquired (dendritic cell) immunity. We have assessed the capacity for synthesis of 1,25(OH)(2)D(3) in these cells and the functional significance of autocrine responses to 1alpha-hydroxylase. Data suggest that local synthesis of 1,25(OH)(2)D(3) may be a preferred mode of response to antigenic challenge in many tissues.
The Journal of Steroid Biochemistry and Molecular Biology 04/2007; 103(3-5):316-21. · 3.98 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An essential element of the innate immune response to injury is the capacity to recognize microbial invasion and stimulate production of antimicrobial peptides. We investigated how this process is controlled in the epidermis. Keratinocytes surrounding a wound increased expression of the genes coding for the microbial pattern recognition receptors CD14 and TLR2, complementing an increase in cathelicidin antimicrobial peptide expression. These genes were induced by 1,25(OH)2 vitamin D3 (1,25D3; its active form), suggesting a role for vitamin D3 in this process. How 1,25D3 could participate in the injury response was explained by findings that the levels of CYP27B1, which converts 25OH vitamin D3 (25D3) to active 1,25D3, were increased in wounds and induced in keratinocytes in response to TGF-beta1. Blocking the vitamin D receptor, inhibiting CYP27B1, or limiting 25D3 availability prevented TGF-beta1 from inducing cathelicidin, CD14, or TLR2 in human keratinocytes, while CYP27B1-deficient mice failed to increase CD14 expression following wounding. The functional consequence of these observations was confirmed by demonstrating that 1,25D3 enabled keratinocytes to recognize microbial components through TLR2 and respond by cathelicidin production. Thus, we demonstrate what we believe to be a previously unexpected role for vitamin D3 in innate immunity, enabling keratinocytes to recognize and respond to microbes and to protect wounds against infection.
Journal of Clinical Investigation 04/2007; 117(3):803-11. · 12.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We investigated the regulation of T-cell homing receptors in infectious disease by evaluating the cutaneous lymphocyte antigen (CLA) in human leprosy. We found that CLA-positive cells were enriched in the infectious lesions associated with restricting the growth of the pathogen Mycobacterium leprae, as assessed by the clinical course of infection. Moreover, CLA expression on T cells isolated from the peripheral blood of antigen-responsive tuberculoid leprosy patients increased in the presence of M. leprae (2.4-fold median increase; range 0.8-6.1, n = 17), but not in unresponsive lepromatous leprosy patients (1.0-fold median increase; range 0.1-2.2, n = 10; P < 0.005). Mycobacterium leprae specifically up-regulated the skin homing receptor, CLA, but not alpha(4)/beta(7), the intestinal homing receptor, which decreased on T cells of patients with tuberculoid leprosy after antigen stimulation (2.2-fold median decrease; range 1.6-3.4, n = 3). Our data indicate that CLA expression is regulated during the course of leprosy infection and suggest that T-cell responsiveness to a microbial antigen directs antigen-specific T cells to the site of infection.
[Show abstract][Hide abstract] ABSTRACT: It has been well established that Toll-like receptors (TLRs) are expressed by keratinocytes and respond to their respective ligands to initiate immune responses. However, it appears that keratinocytes, via differential activation of TLRs, may play a key role in determining the type of subsequent cutaneous immune response generated against a particular pathogen.
Journal of Investigative Dermatology 03/2007; 127(2):262-3. · 6.19 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Cathelicidins are antimicrobial peptides of the innate immune system that establish an antimicrobial barrier at epithelial interfaces and have been proposed to have a proinflammatory function. We studied the role of cathelicidin in allergic contact dermatitis, a model requiring dendritic cells of the innate immune response and T cells of the adaptive immune response. Deletion of the murine cathelicidin gene Cnlp enhanced an allergic contact response, whereas local administration of cathelicidin before sensitization inhibited the allergic response. Cathelicidins inhibited TLR4 but not TLR2 mediated induction of dendritic cell maturation and cytokine release, and this inhibition was associated with an alteration of cell membrane function and structure. Further analysis in vivo connected these observations because inhibition of sensitization by exogenous cathelicidin was dependent on the presence of functional TLR4. These observations provide evidence that cathelicidin antimicrobial peptides mediate an anti-inflammatory response in part by their activity at the membrane.
The Journal of Immunology 03/2007; 178(3):1829-34. · 5.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Here we identified Ito cells (hepatic stellate cells, HSC), known for storage of vitamin A and participation in hepatic fibrosis, as professional liver-resident antigen-presenting cells (APC). Ito cells efficiently presented antigens to CD1-, major histocompatibility complex (MHC)-I-, and MHC-II-restricted T cells. Ito cells presented lipid antigens to CD1-restricted T lymphocytes such as natural killer T (NKT) cells and promoted homeostatic proliferation of liver NKT cells through interleukin-15. Moreover, Ito cells presented antigenic peptides to CD8(+) and CD4(+) T cells and mediated crosspriming of CD8(+) T cells. Peptide-specific T cells were activated by transgenic Ito cells presenting endogenous neoantigen. Upon bacterial infection, Ito cells elicited antigen-specific T cells and mediated protection. In contrast to other liver cell types that have been implicated in induction of immunological tolerance, our data identify Ito cells as professional intrahepatic APCs activating T cells and eliciting a multitude of T cell responses specific for protein and lipid antigens.
[Show abstract][Hide abstract] ABSTRACT: Viral infections and antiviral responses have been linked to several metabolic diseases, including Reye's syndrome, which is aspirin-induced hepatotoxicity in the context of a viral infection. We identify an interferon regulatory factor 3 (IRF3)-dependent but type I interferon-independent pathway that strongly inhibits the expression of retinoid X receptor alpha (RXRalpha) and suppresses the induction of its downstream target genes, including those involved in hepatic detoxification. Activation of IRF3 by viral infection in vivo greatly enhances bile acid- and aspirin-induced hepatotoxicity. Our results provide a critical link between the innate immune response and host metabolism, identifying IRF3-mediated down-regulation of RXRalpha as a molecular mechanism for pathogen-associated metabolic diseases.
Journal of Experimental Medicine 12/2006; 203(12):2589-602. · 13.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: CD1d-restricted NKT cells expressing invariant TCR alpha-chains (iNKT cells) produce both proinflammatory and anti-inflammatory cytokines rapidly upon activation, and are believed to play an important role in both host defense and immunoregulation. To address the potential implications of iNKT cell responses for infectious or inflammatory diseases of the nervous system, we investigated the expression of CD1d in human peripheral nerve. We found that CD1d was expressed on the surface of Schwann cells in situ and on primary or immortalized Schwann cell lines in culture. Schwann cells activated iNKT cells in a CD1d-dependent manner in the presence of alpha-galactosylceramide. Surprisingly, the cytokine production of iNKT cells stimulated by alpha-galactosylceramide presented by CD1d+ Schwann cells showed a predominance of Th2-associated cytokines such as IL-5 and IL-13 with a marked deficiency of proinflammatory Th1 cytokines such as IFN-gamma or TNF-alpha. Our findings suggest a mechanism by which iNKT cells may restrain inflammatory responses in peripheral nerves, and raise the possibility that the expression of CD1d by Schwann cells could be relevant in the pathogenesis of infectious and inflammatory diseases of the peripheral nervous system.
The Journal of Immunology 11/2006; 177(8):5226-35. · 5.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A key target of many intracellular pathogens is the macrophage. Although macrophages can generate antimicrobial activity, neutrophils have been shown to have a key role in host defense, presumably by their preformed granules containing antimicrobial agents. Yet the mechanism by which neutrophils can mediate antimicrobial activity against intracellular pathogens such as Mycobacterium tuberculosis has been a long-standing enigma. We demonstrate that apoptotic neutrophils and purified granules inhibit the growth of extracellular mycobacteria. Phagocytosis of apoptotic neutrophils by macrophages results in decreased viability of intracellular M. tuberculosis. Concomitant with uptake of apoptotic neutrophils, granule contents traffic to early endosomes, and colocalize with mycobacteria. Uptake of purified granules alone decreased growth of intracellular mycobacteria. Therefore, the transfer of antimicrobial peptides from neutrophils to macrophages provides a cooperative defense strategy between innate immune cells against intracellular pathogens and may complement other pathways that involve delivery of antimicrobial peptides to macrophages.
The Journal of Immunology 09/2006; 177(3):1864-71. · 5.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Langerhans cells (LC) are a unique subset of dendritic cells (DC), present in the epidermis and serving as the first line of defense against pathogens invading the skin. To investigate the role of human LCs in innate immune responses, we examined TLR expression and function of LC-like DCs derived from CD34+ progenitor cells and compared them to DCs derived from peripheral blood monocytes (monocyte-derived DC; Mo-DC). LC-like DCs and Mo-DCs expressed TLR1-10 mRNAs at comparable levels. Although many of the TLR-induced cytokine patterns were similar between the two cell types, stimulation with the TLR3 agonist poly(I:C) triggered significantly higher amounts of the IFN-inducible chemokines CXCL9 (monokine induced by IFN-gamma) and CXCL11 (IFN-gamma-inducible T cell alpha chemoattractant) in LC-like DCs as compared with Mo-DCs. Supernatants from TLR3-activated LC-like DCs reduced intracellular replication of vesicular stomatitis virus in a type I IFN-dependent manner. Finally, CXCL9 colocalized with LCs in skin biopsy specimens from viral infections. Together, our data suggest that LCs exhibit a direct antiviral activity that is dependent on type I IFN as part of the innate immune system.
The Journal of Immunology 08/2006; 177(1):298-305. · 5.52 Impact Factor