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Peter A Sieling

Publications and source records attributed to Peter A Sieling.

At least 19 recordsLinked to original sources
PubMed2006

Functional characterization of a T-cell receptor BV6+ T-cell clone derived from a leprosy lesion.

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.

Antigens, Bacterial↗
PubMed2006

Expression of CD1d molecules by human schwann cells and potential interactions with immunoregulatory invariant NK T cells.

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.

Antigens, CD1↗
PubMed2006

TLR activation of Langerhans cell-like dendritic cells triggers an antiviral immune response.

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.

Cell Line↗
PubMed2006

Inducible costimulator: a modulator of IFN-gamma production in human tuberculosis.

Effective host defense against Mycobacterium tuberculosis requires the induction of Th1 cytokine responses. We investigated the regulated expression and functional role of the inducible costimulator (ICOS), a receptor known to regulate Th cytokine production, in the context of human tuberculosis. Patients with active disease, classified as high responder (HR) or low responder (LR) patients according to their in vitro T cell responses against the Ag, were evaluated for T cell expression of ICOS after M. tuberculosis-stimulation. We found that ICOS expression significantly correlated with IFN-gamma production by tuberculosis patients. ICOS expression levels were regulated in HR patients by Th cytokines: Th1 cytokines increased ICOS levels, whereas Th2-polarizing conditions down-regulated ICOS in these individuals. Besides, in human polarized Th cells, engagement of ICOS increased M. tuberculosis IFN-gamma production with a magnitude proportional to ICOS levels on those cells. Moreover, ICOS ligation augmented Ag-specific secretion of the Th1 cytokine IFN-gamma from responsive individuals. In contrast, neither Th1 nor Th2 cytokines dramatically affected ICOS levels on Ag-stimulated T cells from LR patients, and ICOS activation did not enhance IFN-gamma production. However, simultaneous activation of ICOS and CD3 slightly augmented IFN-gamma secretion by LR patients. Together, our data suggest that the regulation of ICOS expression depends primarily on the response of T cells from tuberculosis patients to the specific Ag. IFN-gamma released by M. tuberculosis-specific T cells modulates ICOS levels, and accordingly, ICOS ligation induces IFN-gamma secretion. Thus, ICOS activation may promote the induction of protective Th1 cytokine responses to intracellular bacterial pathogens.

Antibodies, Monoclonal↗
PubMed2005

TGF-alpha regulates TLR expression and function on epidermal keratinocytes.

The expression of TLRs on epithelial cells provides a first line of defense against invading pathogens. We investigated the regulated expression and function of TLR5 and TLR9 on human keratinocytes, because we found by immunohistochemistry that these TLRs are expressed in distinct layers of the epidermis. We found that TGF-alpha, a growth and differentiation factor that is present during wound healing and in psoriasis, increased the expression of both TLR5 and TLR9 on keratinocytes. In addition, TGF-alpha regulated the function of TLR5 and TLR9, because activation with their respective ligands enhanced the production of IL-8 and human beta-defensins. These findings provide evidence that TGF-alpha up-regulates TLR expression and function, augmenting host defense mechanisms at epithelial surfaces.

Adjuvants, Immunologic↗
PubMed2005

TLR activation triggers the rapid differentiation of monocytes into macrophages and dendritic cells.

Leprosy enables investigation of mechanisms by which the innate immune system contributes to host defense against infection, because in one form, the disease progresses, and in the other, the infection is limited. We report that Toll-like receptor (TLR) activation of human monocytes induces rapid differentiation into two distinct subsets: DC-SIGN+ CD16+ macrophages and CD1b+ DC-SIGN- dendritic cells. DC-SIGN+ phagocytic macrophages were expanded by TLR-mediated upregulation of interleukin (IL)-15 and IL-15 receptor. CD1b+ dendritic cells were expanded by TLR-mediated upregulation of granulocyte-macrophage colony-stimulating factor (GM-CSF) and its receptor, promoted T cell activation and secreted proinflammatory cytokines. Whereas DC-SIGN+ macrophages were detected in lesions and after TLR activation in all leprosy patients, CD1b+ dendritic cells were not detected in lesions or after TLR activation of peripheral monocytes in individuals with the progressive lepromatous form, except during reversal reactions in which bacilli were cleared by T helper type 1 (TH1) responses. In tuberculoid lepromatous lesions, DC-SIGN+ cells were positive for macrophage markers, but negative for dendritic cell markers. Thus, TLR-induced differentiation of monocytes into either macrophages or dendritic cells seems to crucially influence effective host defenses in human infectious disease.

Antigens, CD1↗
PubMed2005

The human CD1-restricted T cell repertoire is limited to cross-reactive antigens: implications for host responses against immunologically related pathogens.

The repertoires of CD1- and MHC-restricted T cells are complementary, permitting the immune recognition of both lipid and peptide Ags, respectively. To compare the breadth of the CD1-restricted and MHC-restricted T cell repertoires, we evaluated T cell responses against lipid and peptide Ags of mycobacteria in leprosy, comparing tuberculoid patients, who are able to restrict the pathogen, and lepromatous patients, who have disseminated infection. The striking finding was that in lepromatous leprosy, T cells did not efficiently recognize lipid Ags from the leprosy pathogen, Mycobacterium leprae, or the related species, Mycobacterium tuberculosis, yet were able to efficiently recognize peptide Ags from M. tuberculosis, but not M. leprae. To identify a mechanism for T cell unresponsiveness against mycobacterial lipid Ags in lepromatous patients, we used T cell clones to probe the species specificity of the Ags recognized. We found that the majority of M. leprae-reactive CD1-restricted T cell clones (92%) were cross-reactive for multiple mycobacterial species, whereas the majority of M. leprae-reactive MHC-restricted T cells were species specific (66%), with a limited number of T cell clones cross-reactive (34%) with M. tuberculosis. In comparison with the MHC class II-restricted T cell repertoire, the CD1-restricted T cell repertoire is limited to recognition of cross-reactive Ags, imparting a distinct role in the host response to immunologically related pathogens.

Adult↗
PubMed2004

Activation of signaling lymphocytic activation molecule triggers a signaling cascade that enhances Th1 responses in human intracellular infection.

T cell production of IFN-gamma contributes to host defense against infection by intracellular pathogens, including mycobacteria. Lepromatous leprosy, the disseminated form of infection caused by Mycobacterium leprae, is characterized by loss of cellular response against the pathogen and diminished Th1 cytokine production. Relieving bacterial burden in Ag-unresponsive patients might be achieved through alternative receptors that stimulate IFN-gamma production. We have previously shown that ligation of signaling lymphocytic activation molecule (SLAM) enhances IFN-gamma in mycobacterial infection; therefore, we investigated molecular pathways leading from SLAM activation to IFN-gamma production in human leprosy. The expression of the SLAM-associated protein (an inhibitory factor for IFN-gamma induction) on M. leprae-stimulated cells from leprosy patients was inversely correlated to IFN-gamma production. However, SLAM ligation or exposure of cells from lepromatous patients to a proinflammatory microenvironment down-regulated SLAM-associated protein expression. Moreover, SLAM activation induced a sequence of signaling proteins, including activation of the NF-kappaB complex, phosphorylation of Stat1, and induction of T-bet expression, resulting in the promotion of IFN-gamma production, a pathway that remains quiescent in response to Ag in lepromatous patients. Therefore, our findings reveal a cascade of molecular events during signaling through SLAM in leprosy that cooperate to induce IFN-gamma production and strongly suggest that SLAM might be a focal point for therapeutic modulation of T cell cytokine responses in diseases characterized by dysfunctional Th2 responses.

Adjuvants, Immunologic↗
PubMed2004

Truncated structural variants of lipoarabinomannan in Mycobacterium leprae and an ethambutol-resistant strain of Mycobacterium tuberculosis.

Current knowledge on the structure of lipoarabinomannan (LAM) has resulted primarily from detailed studies on a few selected laboratory strains of Mycobacterium tuberculosis, Mycobacterium bovis BCG, and Mycobacterium smegmatis. Our previous work was the first to report on the salient structural features of M. tuberculosis clinical isolates and demonstrated significant structural variations. A prime effort is to correlate a particular structural characteristic with observed differences in eliciting an immunobiological response, especially in the context of CD1-restricted presentation of LAM to T cells. T cell clones derived from the cutaneous lesions of leprosy patients have been shown to recognize specifically LAM from Mycobacterium leprae and not from M. tuberculosis Erdman or H37Rv. Herein we provide further fine structural data on LAM from M. leprae (LepLAM) and a tuberculosis clinical isolate, CSU20 (CSU20LAM), which was unexpectedly recognized by the supposedly LepLAM-specific CD1-restricted T cell clones. In comparison with the de facto laboratory LAM standard from M. tuberculosis H37Rv (RvLAM), LepLAM derived from in vivo grown M. leprae is apparently simpler in its arabinan architecture with a high degree of exposed, non-mannose-capped termini. On the other hand, CSU20, an ethambutol-resistant clinical isolate, makes a vastly heterogeneous population of LAM ranging from rather small and non-mannose-capped to full-length and fully capped variants. LepLAM and CSU20LAM contain a higher level of succinylation than RvLAM, which, in the context of truncated or less elaborated arabinan, may contribute to selective recognition by T cells. LAM from all species could be resolved into discrete forms by isoelectric focusing based apparently on their arabinan heterogeneity. In the light of our current and more recent findings, we reason that all immunobiological data should be cautiously interpreted and that the actual LAM variants that may be present in vivo during infection and pathogenesis need to be taken into consideration.

Blotting, Western↗
PubMed2004

Expression of signaling lymphocytic activation molecule-associated protein interrupts IFN-gamma production in human tuberculosis.

Production of the Th1 cytokine IFN-gamma by T cells is considered crucial for immunity against Mycobacterium tuberculosis infection. We evaluated IFN-gamma production in tuberculosis in the context of signaling molecules known to regulate Th1 cytokines. Two populations of patients who have active tuberculosis were identified, based on their T cell responses to the bacterium. High responder tuberculosis patients displayed significant M. tuberculosis-dependent T cell proliferation and IFN-gamma production, whereas low responder tuberculosis patients displayed weak or no T cell responses to M. tuberculosis. The expression of the signaling lymphocytic activation molecule (SLAM)-associated protein (SAP) on cells from tuberculosis patients was inversely correlated with IFN-gamma production in those individuals. Moreover, patients with a nonfunctional SAP gene displayed immune responses to M. tuberculosis similar to those of high responder tuberculosis patients. In contrast to SAP, T cell expression of SLAM was directly correlated with responsiveness to M. tuberculosis Ag. Our data suggest that expression of SAP interferes with Th1 responses whereas SLAM expression contributes to Th1 cytokine responses in tuberculosis. The study further suggests that SAP and SLAM might be focal points for therapeutic modulation of T cell cytokine responses in tuberculosis.

Adjuvants, Immunologic↗
PubMed2004

Saposin C is required for lipid presentation by human CD1b.

Lipids from Mycobacterium tuberculosis are presented through CD1 proteins to T lymphocytes in humans, but the accessory molecules required for antigen loading and presentation remain unidentified. Here we show that fibroblasts deficient in sphingolipid activator proteins (SAPs) transfected with CD1b failed to activate lipid-specific T cells. However, the T cell response was restored when fibroblasts were reconstituted with SAP-C but not other SAPs. Lipid antigen and SAP-C colocalized in lysosomal compartments, and liposome assays showed that SAP-C efficiently extracts antigen from membranes. Coprecipitation demonstrated direct molecular interaction between SAP-C and CD1b. We propose a model in which SAP-C exposes lipid antigens from intralysosomal membranes for loading onto CD1b. Thus, SAP-C represents a missing link in antigen presentation of lipids through CD1b to human T cells.

Antigen Presentation↗
PubMed2004

Langerhans cells utilize CD1a and langerin to efficiently present nonpeptide antigens to T cells.

Langerhans cells (LCs) constitute a subset of DCs that initiate immune responses in skin. Using leprosy as a model, we investigated whether expression of CD1a and langerin, an LC-specific C-type lectin, imparts a specific functional role to LCs. LC-like DCs and freshly isolated epidermal LCs presented nonpeptide antigens of Mycobacterium leprae to T cell clones derived from a leprosy patient in a CD1a-restricted and langerin-dependent manner. LC-like DCs were more efficient at CD1a-restricted antigen presentation than monocyte-derived DCs. LCs in leprosy lesions coexpress CD1a and langerin, placing LCs in position to efficiently present a subset of antigens to T cells as part of the host response to human infectious disease.

Antigen Presentation↗
PubMed2003

Apoptosis facilitates antigen presentation to T lymphocytes through MHC-I and CD1 in tuberculosis.

Protective immunity against Mycobacterium tuberculosis involves major histocompatibility complex class I (MHC-I)- and CD1-restricted CD8 T cells, but the mechanisms underlying antigen delivery to antigen-presenting molecules remain enigmatic. Macrophages, the primary host cells for mycobacteria, are CD1-negative. Here we show that M. tuberculosis phagosomes are secluded from the cytosolic MHC-I processing pathway and that mycobacteria-infected cells lose their antigen-presenting capacity. We also show that mycobacteria induce apoptosis in macrophages, causing the release of apoptotic vesicles that carry mycobacterial antigens to uninfected antigen-presenting cells (APCs). Inhibition of apoptosis reduced transfer of antigens to bystander cells and activation of CD8 T cells. Uninfected dendritic cells, which engulfed extracellular vesicles, were indispensable for subsequent cross-presentation of antigens, through MHC-I and CD1b, to T cells from mycobacteria-sensitized donors. This new 'detour' pathway for presentation of antigens from a phagosome-contained pathogen shows the functional significance of infection-induced apoptosis in the activation of CD8 T cells specific for both protein and glycolipid antigens in tuberculosis.

Animals↗
PubMed2003

Activation and regulation of Toll-like receptors 2 and 1 in human leprosy.

The expression and activation of Toll-like receptors (TLRs) was investigated in leprosy, a spectral disease in which clinical manifestations correlate with the type of immune response mounted toward Mycobacterium leprae. TLR2-TLR1 heterodimers mediated cell activation by killed M. leprae, indicating the presence of triacylated lipoproteins. A genome-wide scan of M. leprae detected 31 putative lipoproteins. Synthetic lipopeptides representing the 19-kD and 33-kD lipoproteins activated both monocytes and dendritic cells. Activation was enhanced by type-1 cytokines and inhibited by type-2 cytokines. In addition, interferon (IFN)-gamma and granulocyte-macrophage colony-stimulating factor (GM-CSF) enhanced TLR1 expression in monocytes and dendritic cells, respectively, whereas IL-4 downregulated TLR2 expression. TLR2 and TLR1 were more strongly expressed in lesions from the localized tuberculoid form (T-lep) as compared with the disseminated lepromatous form (L-lep) of the disease. These data provide evidence that regulated expression and activation of TLRs at the site of disease contribute to the host defense against microbial pathogens.

Animals↗
PubMed2003

A role for triggering receptor expressed on myeloid cells-1 in host defense during the early-induced and adaptive phases of the immune response.

Triggering receptor expressed on myeloid cells (TREM)-1 is a cell surface molecule expressed on neutrophils and monocytes implicated in the propagation of the inflammatory response. To further characterize the function of this molecule in different phases of the immune response, we examined TREM-1 in the context of host defense against microbial pathogens. In primary human monocytes TREM-1 activation did not trigger innate antimicrobial pathways directed against intracellular Mycobacterium tuberculosis, and only minimally improved phagocytosis. However, activation of TREM-1 on monocytes did drive robust production of proinflammatory chemokines such as macrophage inflammatory protein-1alpha and IL-8. Engagement of TREM-1 in combination with microbial ligands that activate Toll-like receptors also synergistically increased production of the proinflammatory cytokines TNF-alpha and GM-CSF, while inhibiting production of IL-10, an anti-inflammatory cytokine. Expression of TREM-1 was up-regulated in response to TLR activation, an effect further enhanced by GM-CSF and TNF-alpha but inhibited by IL-10. Functionally, primary monocytes differentiated into immature dendritic cells following activation through TREM-1, evidenced by higher expression of CD1a, CD86, and MHC class II molecules. These cells had an improved ability to elicit T cell proliferation and production of IFN-gamma. Our data suggest that activation of TREM-1 on monocytes participates during the early-induced and adaptive immune responses involved in host defense against microbial challenges.

Blood Bactericidal Activity↗
PubMed2003

Toll-like receptor 2 ligands as adjuvants for human Th1 responses.

Bacterial lipopeptides (bLPs) are increasingly used as adjuvants to activate cell-mediated immune responses to foreign Ags. To explore mechanisms whereby bLPs adjuvant T cell responses, we stimulated human PBMCs with bLPs. We found that bLPs stimulate T cells to proliferate and produce IFN-gamma in an accessory cell-dependent manner and in the absence of exogenous protein Ags. The ability of bLPs to stimulate T cell proliferation was Toll-like receptor 2 dependent and required IL-12, interaction with costimulatory molecules, and MHC proteins. Our data suggest that bLPs adjuvant adaptive Th1 responses by enhancing Ag presentation of endogenous peptides.

Adjuvants, Immunologic↗
PubMed2003

Distribution of Toll-like receptor 1 and Toll-like receptor 2 in human lymphoid tissue.

To determine how distinct receptors of the immune system can contribute to innate immunity, we investigated the pattern of Toll-like receptor 1 (TLR1) and TLR2 expression in human lymphoid tissue. We found that TLR1 and TLR2 were co-expressed on cells of the innate immune system, including macrophages and dendritic cells. In addition, TLR1 and TLR2 were expressed in mucosa-associated lymphoid tissue on tonsillar crypt epithelium. Of the lymphoid tissue examined, spleen expressed the highest levels of TLR2. Although TLR1- and TLR2-positive cells were in close proximity to T lymphocytes in vivo, lymphocytes themselves were devoid of TLR1 and TLR2 expression. The co-expression of TLR1 and TLR2 on myeloid cells in lymphoid tissue provides the host with the ability to respond to a variety of microbial ligands at sites conducive to the generation of an immune response.

Dendritic Cells↗