Fas/Fas ligand-mediated elimination of antigen-bearing Langerhans cells in draining lymph nodes

In vivo monitoring of transfected DNA, gene expression kinetics, and cellular immune responses in mice immunized with a human NIS gene-expressing plasmid

In assessing the effectiveness of DNA vaccines, it is important to monitor: (1) the kinetics of target gene expression in vivo; and (2) the movement of cells that become transfected with the plasmid DNA used in the immunization of a subject. In this study, we used, as a visual imaging marker, expression of the transfected human sodium/iodide symporter (hNIS) gene, which enhances intracellular radio-pertechnetate (TcO4-) accumulation. After intradermal (i.d.) and systemic injection of mice with pcDNA-hNIS and radioactive Technetium-99m (Tc-99m), respectively, whole-body images were obtained by nuclear scintigraphy. The migration of mice cells transfected with the hNIS gene was monitored over a 2-week period by gamma-radioactivity counting of isolated cell populations and was demonstrated in peripheral lymphoid tissues, especially in the draining lymph nodes (dLNs). Beginning at 24 h after DNA inoculation and continuing for the 2-week monitoring period, hNIS-expressing cells were observed specifically in the T-cell-rich zones of the paracortical area of the dLNs. Over the same time period, high levels of INF-γ-secreting CD8 T-cells were found in the dLNs of the pcDNA-hNIS immunized mice. Tumor growth was also significantly retarded in the mice that received hNIS DNA immunization followed by inoculation with CT26 colorectal adenocarcinoma cells that had been transfected with the rat NIS gene (rNIS), which is 93% homologous to the hNIS gene. In conclusion, mouse cells transfected with hNIS DNA after i.d. immunization were found to traffic to the dLNs, and hNIS gene expression in these cells continued for at least 2 weeks post immunization. Furthermore, sequential presentation of NIS DNA to T-cells by migratory antigen presenting cells could induce NIS DNA-specific Th1 immune responses and thus retard the growth of NIS-expressing tumors.

CD70 is selectively expressed on Th1 but not on Th2 cells and is required for Th1-type immune responses

The interaction between CD27 and CD70 provides a costimulatory signal for T-cell survival. Although the role of CD27 signaling in CD8(+) T cells has been well defined, its role in CD4(+) T cells is relatively unknown. Here, we report that CD70 is specifically expressed on differentiated T-helper (Th)1 cells, but not on Th2 cells. Upon activation, CD70 expression increased markedly on Th1 cells, but remained undetectable on Th2 cells. We demonstrate that CD27 is involved in naive T-cell expansion in Th1-type, but not in Th2-type, immune responses as in vivo treatment with anti-CD70 monoclonal antibody at induction resulted in a significant reduction of delayed-type and contact hypersensitivity responses, but not asthmatic responses. In both Th1-type responses, during the priming phase, CD70 was detected at earlier time points on dendritic cells (DCs) and at later time points on CD4(+) T cells. Our results indicate that CD70 may be useful as a marker to distinguish Th1 from Th2 cells. More importantly, CD27 function may be controlled by the differentially regulated kinetics of CD70 expression on DCs and CD4(+) T cells, and Th1 cell-specific CD70 expression may be involved in an amplification loop for polarized Th1-type immune responses through T cell-T cell interactions.

CD4+CD25+ regulatory T cells utilize FasL as a mechanism to restrict DC priming functions in cutaneous immune responses

Recent studies have suggested Fas-mediated elimination of antigen-presenting cells as an important mechanism down-regulating the induction of autoimmune responses. It remains unknown whether this mechanism restricts the magnitude of immune responses to non-self antigens. We used a mouse model of a cutaneous CD8(+) T-cell-mediated immune response (contact hypersensitivity, CHS) to test if CD4(+)CD25(+) T cells expressing FasL regulate hapten-specific effector CD8(+) T cell expansion through the elimination of Fas-expressing hapten-presenting DC. In WT mice, attenuation of CD4(+)CD25(+) T regulatory cell activity by anti-CD25 mAb increased hapten-presenting DC numbers in skin-draining LN, which led to increased effector CD8(+) T-cell priming for CHS responses. In contrast, CD4(+)CD25(+) T cells did not regulate hapten-specific CD8(+) T-cell priming and CHS responses initiated by Fas-defective (lpr) DC. Thus, restricting DC priming functions through Fas-FasL interactions is a potent mechanism employed by CD4(+)CD25(+) regulatory cells to restrict CD8(+) T-cell-mediated allergic immune responses in the skin.

Adjuvant effect of lipopolysaccharide on the induction of contact hypersensitivity to haptens in mice

BACKGROUND

Toll-like receptor (TLR) 4 is a critical receptor and signal transducer for lipopolysaccharide (LPS), a major component of Gram-negative bacteria. The MyD88-independent pathway downstream of TLR4 leads to functional dendritic cell (DC) maturation, although LPS-induced cytokine production from DCs is MyD88-dependent.

OBJECTIVES

We investigated whether intracutaneously injected LPS alters the functions of cutaneous DCs, leading to enhanced contact hypersensitivity (CH).

METHODS

The ear swelling response was measured to evaluate the magnitude of CH. Cell proliferation of allogeneic splenocytes stimulated by DC-enriched draining lymph node (LN) cells was measured by performing a [(3)H]-thymidine incorporation assay. Epidermal I-A+ cells were evaluated under an epifluorescent microscope. I-A+ FITC-bearing cells from the draining LNs 24h after FITC application were analyzed on FACScan.

RESULTS

LPS augmented CH induction in C3H/HeN (HeN) and MyD88-knockout (KO) mice but not in C3H/HeJ (HeJ) and H-2S(d)-bearing strains such as BALB/c mice. LPS failed to augment the allo-stimulatory ability of DCs in the draining LNs after hapten applications. LPS altered the density and morphology of epidermal I-A+ cell in HeN and BALB/c mice but not in TLR4-deficient HeJ mice. LPS increased the proportion of I-A+ FITC-bearing cells in the LNs 24h after FITC application in HeN, but not in BALB/c and HeJ.

CONCLUSIONS

LPS augments the ability of DCs to migrate to the draining LNs, leading to enhanced CH via a TLR4-dependent, MyD88-independent pathway. The different effects of LPS on CH in some strains of mice may explain individual differences in the susceptibility to establish CH to daily antigen exposures in clinical settings.

Spatial and temporal expression of herpes simplex virus type 1 amplicon-encoded genes: implications for their use as immunization vectors

There is great interest in developing new immunization vectors. Helper virus-free herpes amplicons, plasmid-based vectors that encode no viral gene products and have an extremely large coding capacity, are attractive viral vaccine candidates for expressing recombinant proteins in vivo for immunization. Earlier studies in mice, using amplicons encoding the gp120 protein of human immunodeficiency virus (HIV), resulted in strikingly robust cellular immune responses as measured by cytotoxicity and interferon gamma enzyme-linked immunospot assays. To begin to understand how such vectors function in vivo to generate an immune response, we used amplicons encoding reporter constructs including green fluorescent protein (GFP) and luciferase to examine the duration of expression after administration to mice. Luciferase expression, measured with the IVIS system from Xenogen/Caliper Life Sciences (Hopkinton, MA) and by enzymatic assays of tissue extracts, revealed that expression after injection of the HSVluc amplicons peaked earlier than 24 hr after injection into mice. HSVegfp injection resulted in peak accumulation of GFP 24 hr after administration in vivo. Thus, both reporter genes revealed a rather rapid and robust expression pattern of short duration. The short period of expression appears in part to be due to gene silencing. Examination of the cells transduced by amplicons encoding GFP and human B7.1 suggested that the amplicons transduce a variety of cells, including professional antigen-presenting cells. From this and previous work, we conclude that amplicons may engender a potent immune response by directly transducing dendritic cells as well as by cross-priming of antigen produced by other transduced host cells.

CD4 T cell-induced, bid-dependent apoptosis of cutaneous dendritic cells regulates T cell expansion and immune responses

The fate of dendritic cells (DCs) after Ag presentation may be DC subset-specific and controlled by many factors. The role of activation-induced apoptosis in regulating DC function is not clear. We investigated the fate of cutaneous DCs (cDCs), specifically Langerhans cells (LCs), and observed that they undergo apoptosis after successful Ag presentation to CD4 T cells. Caspase-specific inhibitors revealed that LC lines use a type II apoptosis pathway in response to CD4 T cells. In support of this, BH3-interacting domain (Bid) protein was present at high levels and specifically cleaved in the presence of Ag-specific T cells. Significant resistance to apoptosis by OT-2 CD4 cells was also observed for Bid knockout (KO) LCs in vitro. To test whether Bid was required to regulate LC function in vivo, we measured contact sensitization and topical immunization responses in Bid KO mice and observed markedly enhanced ear swelling and proliferation responses compared with wild-type mice. Furthermore, when Ag-pulsed Bid KO migratory cDCs were inoculated into wild-type recipients, an increase in both the rate and percentage of expanded OT-2 T cells expressing IFN-gamma was observed. Thus, enhanced Ag presentation function was intrinsic to Bid KO cDCs. Therefore, Bid is an important regulator of LC viability and Ag presentation function.

Corticosteroids But Not Pimecrolimus Affect Viability, Maturation and Immune Function of Murine Epidermal Langerhans Cells

Given the importance of dendritic cells in the immune response, we investigated the effect of corticosteroids (CS) on the integrity, survival, and function of murine Langerhans cells (LC) in comparison with pimecrolimus, a novel anti-inflammatory drug for the topical treatment of atopic dermatitis. BALB/c mice were treated twice on one day with ethanolic solutions of the compounds. At 24-72 h after the last application, we observed fragmented DNA, caspase-3 activity, and an upregulation of CD95 expression in LC from mice treated with CS but not in LC of pimecrolimus- or vehicle-treated animals. CS-epidermal cell (EC) supernatants but not pimecrolimus-EC supernatants contained significantly lower amounts of soluble factors (GM-CSF, TNF-alpha, IL-1alpha) required for LC survival and maturation than EC supernatants from vehicle-treated mice. With regard to LC maturation, CS but not pimecrolimus inhibited the expression of CD25, CD205, and costimulatory molecules. In line with this, LC from pimecrolimus-treated mice were similar to LC from vehicle-treated mice in their capacity to stimulate antigen-presenting function and migration, whereas LC from CS-treated mice were greatly impaired in these abilities. In summary, our data show for the first time that CS but not pimecrolimus induce apoptosis in LC in situ, implying that the prolonged use of CS could have adverse effects on the skin immune system.

CD1a and CD1c cell sorting yields a homogeneous population of immature human Langerhans cells

There is increasing evidence that ex vivo generated Langerhans cells (LCs) cannot fully substitute for their physiological counterparts in normal epidermis when studying the immunobiology of this prototype of a tissue-residing immature dendritic cell (DC). Here, we present CD1-based magnetic-activated cell-sorting (MACS) protocols for the effective isolation of human epidermal LCs. CD1c selection yielded a homogeneous population of pure and viable HLA-DR(+)/CD1a(+) DCs, with the ultrastructural features, surface antigen expression and cytokine profile, characteristic of epidermis-resident immature LCs. The immature state and functional integrity were established by allogeneic mixed lymphocyte reactions showing a weak stimulatory capacity of freshly isolated cells and upregulation upon stimulation. Characterizing the cells in more detail, we could demonstrate for the first time that normal human LCs express CXCR4, CD40 ligand (CD40L), and Fas and Fas ligand (FasL). The observed constitutive transcription of TGF-beta suggests that the viability and immature state of epidermal LCs are maintained not only by the TGF-beta production from the microenvironment, but also in an autocrine or paracrine manner. LPS and IFN-omega stimulated the expression of the inflammatory cytokines TNF-alpha and IL-1beta, and there was secretion of IL-12p70 after CD40 ligation. Remarkably, the CD1-sorted LCs showed no loss of their Birbeck granules and CD1a expression upon culturing and no spontaneous phenotypic and functional maturation into potent antigen-presenting cells (APCs). We conclude that human epidermal LCs obtained by the CD1c cell-sorting protocol are optimal candidates with which to elucidate the properties and capabilities of immature cells and to develop immunotherapeutic vaccines.

Cell-mediated fas-based lysis of dendritic cells which are apparently resistant to anti-Fas antibody

In this report, the controversy concerning the sensitivity of dendritic cells (DCs) to Fas-dependent induction of apoptosis was examined using murine DCs. Although DCs could not be lysed when exposed to an anti-Fas antibody, Jo2, the observed resistance turned out to reflect their lack of the expression of Fc(gamma)R necessary for crosslinking the antibody, rather than their intrinsic resistance. Thus, at least a fraction of DCs was sensitive to Jo2 in the presence of Fc(gamma)R-expressing by-standers. Consistently, a significant fraction of DCs was sensitive to Fas-dependent lysis mediated by T cells including the antigen-specific killing by CD4+ T cells. Both immature (class II MHClow) and mature (class II MHChigh) DCs were sensitive to the Fas-based induction of apoptosis.

Potentiation of Fas-mediated apoptosis by an engineered glycosylphosphatidylinositol-linked Fas

FasL and TRAIL are apoptotic ligands of the TNF-like cytokines family, acting via activation of the transmembrane death domain containing receptors Fas for FasL, and DR4 or DR5 for TRAIL. A glycosylphosphatidylinositol-linked TRAIL receptor called DcR1 behaves as a decoy receptor inhibiting TRAIL-mediated cell death in several cellular systems. We engineered and stably expressed a chimeric GPI-linked Fas receptor (Fas-GPI) in T-lymphocyte cell lines constitutively expressing functional transmembrane Fas. Surprisingly, despite lacking the death domain region of functional Fas, Fas-GPI was able to significantly increase Fas-mediated cell death triggered by membrane bound or soluble FasL, whereas engagement of Fas-GPI alone did not trigger apoptosis. This potentiating effect, but not transmembrane Fas activation, was selectively inhibited by protein kinase C activation with phorbol esters, demonstrating that Fas-GPI activated a specific synergistic signal transduction pathway. Fas-GPI and transmembrane Fas were localized in distinct membrane compartments, since Fas-GPI, but not transmembrane Fas, was found in the glycolipid-rich membrane microdomains. These results suggest that apoptosis induced by members of this ligand/receptors family may be differentially modulated through other and parallel signalling pathways.

Activation through CD40 ligation induces functional Fas ligand expression by Langerhans cells

Langerhans cells (LC) are professional antigen-presenting cells of dendritic cell (DC) lineage and are critical for the induction of primary immune responses in skin. Following antigenic stimulation, LC migrate to regional lymph nodes and induce antigen-specific activation of T cells. After primary expansion, the majority of T cells undergo Fas/Fas ligand (FasL)-mediated apoptotic cell death, thereby suppressing their excessive expansion. Although recent investigations have indicated an immunoregulatory function for DC, whether LC could be involved in Fas/FasL-mediated suppression of activated T cells is still unclear. In this study, we found that LC express FasL after activation triggered through CD40 molecules on their surface, but not by stimulation with LPS or IFN-gamma. The functional significance of FasL expression by LC was demonstrated using two different assays for apoptosis induced in Jurkat cells. The apoptosis in Jurkat cells was completely blocked by anti-FasL blocking antibody, suggesting a Fas/FasL-mediated mechanism. These results indicate a new feedback mechanism to down-regulate T cell activation by LC through the interaction of the TNF receptor/ligand superfamily, CD40/CD40L and Fas/FasL.

Fas/Fas ligand deficiency results in altered localization of anti-double-stranded DNA B cells and dendritic cells

Autoantibodies directed against dsDNA are found in patients with systemic lupus erythematosus as well as in mice functionally deficient in either Fas or Fas ligand (FasL) (lpr/lpr or gld/gld mice). Previously, an IgH chain transgene has been used to track anti-dsDNA B cells in both nonautoimmune BALB/c mice, in which autoreactive B cells are held in check, and MRL-lpr/lpr mice, in which autoantibodies are produced. In this study, we have isolated the Fas/FasL mutations away from the autoimmune-prone MRL background, and we show that anti-dsDNA B cells in Fas/FasL-deficient BALB/c mice are no longer follicularly excluded, and they produce autoantibodies. Strikingly, this is accompanied by alterations in the frequency and localization of dendritic cells as well as a global increase in CD4 T cell activation. Notably, as opposed to MRL-lpr/lpr mice, BALB-lpr/lpr mice show no appreciable kidney pathology. Thus, while some aspects of autoimmune pathology (e.g., nephritis) rely on the interaction of the MRL background with the lpr mutation, mutations in Fas/FasL alone are sufficient to alter the fate of anti-dsDNA B cells, dendritic cells, and T cells.

Death receptors in cutaneous biology and disease

Death receptors are a growing family of transmembrane proteins that can detect the presence of specific extracellular death signals and rapidly trigger cellular destruction by apoptosis. Expression and signaling by death receptors and their respective ligands is a tightly regulated process essential for key physiologic functions in a variety of organs, including the skin. Several death receptors and ligands, Fas and Fas ligand being the most important to date, are expressed in the skin and have proven to be essential in contributing to its functional integrity. Recent evidence has shown that Fas-induced keratinocyte apoptosis in response to ultraviolet light, prevents the accumulation of pro-carcinogenic p53 mutations by deleting ultraviolet-mutated keratinocytes. Further- more, there is strong evidence that dysregulation of Fas expression and/or signaling contributes to the pathogenesis of toxic epidermal necrolysis, acute cutaneous graft versus host disease, contact hypersensitivity and melanoma metastasis. With these new developments, strategies for modulating the function of death receptor signaling pathways have emerged and provided novel therapeutic possibilities. Specific blockade of Fas, for example with intravenous immunoglobulin preparations that contain specific anti-Fas antibodies, has shown great promise in the treatment of toxic epidermal necrolysis and may also be useful in the treatment acute graft versus host disease. Likewise, induction of death signaling by ultraviolet light can lead to hapten-specific tolerance, and gene transfer of Fas ligand to dendritic cells can be used to induce antigen specific tolerance by deleting antigen-specific T cells. Further developments in this field may have important clinical implications in cutaneous disease.

Fas/Fas ligand-mediated apoptosis of murine Langerhans cells

Epidermal Langerhans cells (LC) are potent antigen-presenting cells (APC), that play a crucial role in initiating cutaneous immune responses. The Fas/Fas ligand pathway has been implicated as an important cellular pathway in the regulation of peripheral immunity. The morphologic, functional and phenotypic characteristics of LC are becoming well-characterized. However, the mechanisms involved in eliminating LC are poorly understood. In this report, we demonstrated that murine epidermal LC constitutively express the Fas antigen (CD95) and the expression was up-regulated by the addition of IFN-gamma in cultures. Interestingly, epidermal LC underwent apoptosis by the addition of both recombinant soluble Fas ligand (FasL) and IFN-gamma, but not by FasL alone. These results suggest that LC may acquire the susceptibility to Fas-mediated apoptosis through up-regulation of the Fas expression by IFN-gamma derived from activated T cells and that the elimination of LC may be important for preventing excess cutaneous inflammatory diseases.