Cell-dendritic Cell Interactions Research Articles

BAT3 Regulates Mycobacterium tuberculosis Protein ESAT-6-Mediated Apoptosis of Macrophages

HLA-B-associated transcript 3 (BAT3), also known as Scythe or BAG6, is a nuclear protein implicated in the control of apoptosis and natural killer (NK) cell-dendritic cell (DC) interaction. We demonstrate that BAT3 modulates the immune response by regulating the function of macrophages. BAT3 is released by macrophages in vitro and it down-regulates nitric oxide and proinflammatory cytokines release in IFN-γ and LPS stimulated macrophages. Furthermore, Mycobacterium tuberculosis-derived protein ESAT-6 (Rv3875) induced transient increase in the expression and release of BAT3 in macrophages. We show that induction of apoptosis by ESAT-6 is dependent on the cleavage of BAT3 by caspase-3 and proteasomal degradation. Our results also indicate that BAT3 regulates ESAT-6-induced apoptosis by interacting with anti-apoptotic protein BCL-2. Taken together, the data suggest that BAT3 plays a role in the early immune response to M. tuberculosis infection and may be a key protein associated with the fate of antigen presenting cells during infection.

Antigen availability is a critical determinant of in vivo CD8+ T cell-dendritic cell interaction kinetics and initiates effector/memory fate decisions (110.21)

Abstract Naïve CD8+ T cells are activated through interactions with antigen (Ag) bearing dendritic cells (DCs) in lymph nodes (LNs). Multiphoton intravital microscopy (MP-IVM) of LNs has demonstrated that T cell activation occurs in three phases. The duration of the initial phase of transient, serial DC-T cell interactions is inversely related to Ag dose. It had been assumed that the second phase, characterized by stable DC-T cell contacts, is necessary for T cell activation, however, here we show that this is not always the case. T cells interacting with DCs presenting Ag at low abundance and with a short half-life did not transition from phase one to phase two, whereas a higher dose of the same Ag yielded robust phase two transition. T cells exposed to either antigenic constellation proliferated and developed equivalent effector functions, including cytokine production and cytotoxicity, over the first two days after priming. There are profound differences in the transcriptome at 12h and 24h after activation between CD8 T cells exposed to antigenic constellations that did or did not promote phase two interactions. Only T cells that had undergone stable contacts gave rise to memory, whereas activating conditions that did not support stable contacts yielded immunological amnesia. T cells can make fate decisions in vivo within a few hours after Ag exposure that result in long-term memory or abortive effector responses and correlate with the kinetics of T cell-DCs interactions.

Altered dendritic cell–natural killer interaction in Kenyan sex workers resistant to HIV-1 infection

Natural killer (NK) cells are members of the innate immune system that play an important role in the defense against viral infection. They are also involved in the regulation of adaptive immune responses through cytokine secretion and the interaction with antigen-presenting cells. However, their role in HIV infection is only partially understood. Here we studied the phenotype and function of NK cells of highly HIV-exposed but seronegative (HESN) uninfected commercial sex workers from Kenya who can be epidemiologically defined as relatively resistant to HIV infection. The purpose of this study was to gain insight into the role of NK cells in mediating resistance to HIV-1. This information can be used to better understand protection from infection which can be used for informing future design of effective prophylactics and therapeutics for HIV. Whole blood samples were collected from study participants and isolated NK cells and dendritic cells were used in assays for phenotyping and cell function. Activated NK cells from resistant women killed autologous immature dendritic cells more efficiently and also secreted more interferon (IFN)-γ than those of uninfected, susceptible women. Interestingly, NK cells from HIV-resistant women were significantly more effective in inducing secretion of IL-12 in immature dendritic cells. These data suggest that an altered NK cell-dendritic cell interaction plays an important role in the protection from infection with HIV-1.

Characterization of mast cell-dendritic cell interactions (147.27)

Abstract Mast cells (MCs), while central to allergy, are recently recognized as functioning in a broader immune context. In addition to mediating dendritic cell (DC) responses through secreted products, MCs also present antigen directly to T-cells. While the ability of MCs to present antigen under certain conditions is clear, their in vivo role in relation to other immune cells is still under investigation. Upon activation of MCs, a variety of soluble factors are secreted to which DCs respond including TNFα, prostaglandins, and histamine. Additionally, both MCs and DCs localize within many of the same tissues, and, as we demonstrate, reside in close proximity. Thus, it is possible that MCs and DCs could work in conjunction to mediate immune responses through both indirect and direct mechanisms. To characterize MC-DC interactions, we use a combination of ELISAs, flow cytometry, immunohistochemistry, and live cell confocal microscopy. We show that MCs and DCs form prolonged interactions in the presence of multivalent antigen responsible for crosslinking IgE-primed FcϵRI and activating MCs. These direct interactions result in material transfer from MCs to DCs without inducing DC maturation. Both the exchange of soluble mediators and cell-cell contact resulted in the production of anti-inflammatory cytokines. Interestingly, direct contact appears to induce a stronger albeit delayed response.

Effect of the administration of Lactobacillus paracasei subsp. paracasei NTU 101 on Peyer's patch-mediated mucosal immunity

The role of lactic acid bacteria in gut mucosal immunity was investigated by comparing the enhanced effects in the Peyer's patches and spleen of BALB/c mice fed daily with Lactobacillus paracasei subsp. paracasei NTU 101 for 3 to 9 weeks. After feeding with Lactobacillus, the percentage of CD4 + T cells in both Peyer's patches and the spleen was significantly increased; however, expression of CD 154 molecules, which play a pivotal role in cell-to-cell communication, on CD4 + T cells and the percentage of B220 + B cells increased only in Peyer's patches. Compared with systemic serum IgA, Peyer's patch-derived immunomodulation induced higher levels of intestinal IgA +-producing cells in the lamina propria. Our data also showed that feeding with Lactobacillus induced stronger CD4 + T cell-dendritic cell interaction, enhanced CD4 + T cell and B cell proliferation, and increased IL-1β, IL-10, IL-12, IFN-γ, and TNF-α mRNA expression in Peyer's patches, but not in the spleen. Here, we demonstrate that following Lactobacillus treatment, Peyer's patches exhibited a more distinct capacity to induce CD4 + T cell-dendritic cell interactions, lymphocyte proliferation, and cytokine secretion than the spleen, and thereby promoted greater intestinal IgA production that could enhance immunosurveillance to prevent intestinal infections or other intestinal pathologies.

Mast Cells, Histamine, and IL-6 Regulate the Selective Influx of Dendritic Cell Subsets into an Inflamed Lymph Node

In response to bacterial stimuli, multiple dendritic cell (DC) populations accumulate within the draining lymph node, thus enhancing opportunities for effective T cell-DC interaction. DC subpopulations, such as plasmacytoid, CD8(+), and CD11b(+) subsets, have distinct roles in determining the nature of the immune response. The mechanisms whereby individual DC subpopulations are mobilized and the extent to which these processes are linked to increases in overall lymph node cellularity have not been determined. In the current study, the mechanisms of DC subset mobilization to the draining auricular lymph node were examined after intradermal injection of Staphylococcus aureus-derived peptidoglycan. Using mast cell-deficient mice and local mast cell reconstitution, plasmacytoid and CD8(+) DC responses were shown to be mast cell dependent, whereas the CD11b(+) DC response was not. A histamine H2 receptor-dependent, CXCL9-independent pathway controlled the selective influx of both plasmacytoid and CD11b(+) DC into the lymph node, but not lymph node cellularity. In contrast, IL-6 was important for the mobilization of CD8(+) and CD11b(+) DC. TNF and IL-1 receptor were dispensable for plasmacytoid, CD11b(+), and CD8(+) DC responses. These findings provide novel opportunities for the selective mobilization of specific DC subsets to lymph nodes and demonstrate critical roles for both histamine and IL-6 in this process.

Regulation of T cell-dendritic cell interactions by IL-7 governs T-cell activation and homeostasis

AbstractInterleukin-7 (IL-7) plays a central role in the homeostasis of the T-cell compartment by regulating T-cell survival and proliferation. Whether IL-7 can influence T-cell receptor (TCR) signaling in T cells remains controversial. Here, using IL-7–deficient hosts and TCR-transgenic T cells that conditionally express IL-7R, we examined antigen-specific T-cell responses in vitro and in vivo to viral infection and lymphopenia to determine whether IL-7 signaling influences TCR-triggered cell division events. In vitro, we could find no evidence that IL-7 signaling could costimulate T-cell activation over a broad range of conditions, suggesting that IL-7 does not directly tune TCR signaling. In vivo, however, we found an acute requirement for IL-7 signaling for efficiently triggering T-cell responses to influenza A virus challenge. Furthermore, we found that IL-7 was required for the enhanced homeostatic TCR signaling that drives lymphopenia-induced proliferation by a mechanism involving efficient contacts of T cells with dendritic cells. Consistent with this, saturating antigen-presenting capacity in vivo overcame the triggering defect in response to cognate peptide. Thus, we demonstrate a novel role for IL-7 in regulating T cell–dendritic cell interactions that is essential for both T-cell homeostasis and activation in vivo.

Live imaging of peripheral T cell-DC interactions in the islets: An emerging axis of autoimmune infiltration (48.15)

Abstract Defining processes of islet infiltration and destruction in Type 1 diabetes (T1D) is important for its prevention and preventing destruction of transplanted islets in diabetic individuals. We hypothesize that T1D onset and persistence is maintained by T cell-dendritic cell (DC) interactions in both the draining pancreatic lymph node (PLN) and the islets. In the steady-state, we found that intra-islet DCs are a uniform semi-mature population that constitutively take up β cell antigens in preparation for antigen presentation. Islet-antigen specific CD8 T cells activated in the PLN trafficked to the islets where they induced maturation of islet DCs. Leukocytic infiltration of the islets and islet DC maturation were dependent on IFN-γ production by T cells. Blockade of antigen processing following T cell activation in the PLN also blocked islet DC maturation but not islet infiltration. This suggests that the DCs require productive antigen-presenting interactions with T cells in the islets for maturation to occur. Through 2-photon imaging of the islets, we visualized sustained interactions of islet-antigen specific CD8 T cells with islet DCs and characterized features of cytotoxicity and dwell-time in this setting. Taken together, these data suggest that directed and synaptic delivery of IFN-γ to intra-islet DCs induces their maturation. This work was funded by the Larry L. Hillblom Foundation and the Juvenile Diabetes Research Foundation.

Real-Time Manipulation of T Cell-Dendritic Cell Interactions In Vivo Reveals the Importance of Prolonged Contacts for CD4 + T Cell Activation

T cells interact with dendritic cells (DCs) for periods lasting from minutes to hours. However, a causal link between the duration of this interaction and the efficiency of T cell activation has not been established in vivo. Employing intravital two-photon imaging, we manipulated T cell-DC interactions in real time and found that the first T cell-DC encounter often resulted in a long-lived interaction. Moreover, the cessation of T cell receptor-major histocompatibility complex signals promoted cellular dissociation, suggesting that antigen availability on DCs regulates contact duration. Finally, at least 6 hr of in vivo T cell-DC interaction were required for naive CD4(+) T cells to undergo clonal expansion. These results establish the importance of prolonged T cell-DC interactions for efficient CD4(+) T cell activation in vivo.

Competition for antigen determines the stability of T cell–dendritic cell interactions during clonal expansion

The regulation of T cell-dendritic cell (DC) contacts during clonal expansion is poorly defined. Although optimal CD4 T cell responses require prolonged exposure to antigen (Ag), it is believed that stable T cell-DC interactions occur only during the first day of the activation process. Here we show that recently activated CD4 T cells are in fact fully competent for establishing contact with Ag-bearing DC. Using two-photon imaging, we found that whereas prolonged interactions between activated T cells and Ag-bearing DCs were infrequent at high T cell precursor frequency, they were readily observed for a period of at least 2 days when lower numbers of T cells were used. We provide evidence that, when present in high numbers, Ag-specific T cells still gained access to the DC surface but were competing for the limited number of sites on DCs with sufficient peptide-MHC complexes for the establishment of a long-lived interaction. Consistent with these findings, we showed that restoration of peptide-MHC level on DCs at late time points was sufficient to recover interactions between activated T cells and DCs. Thus, the period during which CD4 T cells continue to establish stable interactions with DCs is longer than previously thought, and its duration is dictated by both Ag levels and T cell numbers, providing a feedback mechanism for the termination of CD4 T cell responses.

Chemokine-Guided CD4+ T Cell Help Enhances Generation of IL-6RαhighIL-7Rαhigh Prememory CD8+ T Cells

CD4(+) T cells promote effective CD8(+) T cell-mediated immunity, but the timing and mechanistic details of such help remain controversial. Furthermore, the extent to which innate stimuli act independently of help in enhancing CD8(+) T cell responses is also unresolved. Using a noninfectious vaccine model in immunocompetent mice, we show that even in the presence of innate stimuli, CD4(+) T cell help early after priming is required for generating an optimal pool of functional memory CD8(+) T cells. CD4(+) T cell help increased the size of a previously unreported population of IL-6Ralpha(high)IL-7Ralpha(high) prememory CD8(+) T cells shortly after priming that showed a survival advantage in vivo and contributed to the majority of functional memory CD8(+) T cells after the contraction phase. In accord with our recent demonstration of chemokine-guided recruitment of naive CD8(+) T cells to sites of CD4(+) T cell-dendritic cell interactions, the generation of IL-6Ralpha(high)IL-7Ralpha(high) prememory as well as functional memory CD8(+) T cells depended on the early postvaccination action of the inflammatory chemokines CCL3 and CCL4. Together, these findings support a model of CD8(+) T cell memory cell differentiation involving the delivery of key signals early in the priming process based on chemokine-guided attraction of naive CD8(+) T cells to sites of Ag-driven interactions between TLR-activated dendritic cells and CD4(+) T cells. They also reveal that elevated IL-6Ralpha expression by a subset of CD8(+) T cells represents an early imprint of CD4(+) T cell helper function that actively contributes to the survival of activated CD8(+) T cells.

Pathogenic Mechanisms of HIV Disease: The Role of Viral Replication and Immune Activation

HIV replication and the immune response to the virus lead to a state of generalized immune activation, which drives the pathogenesis of HIV disease. HIV-induced immune activation results in increased T-cell turnover (production and destruction), increased death of T cells, a decline in the size of the CD4+ T-cell pool, and a state of activation-induced immunodeficiency. In many HIVinfected individuals, these phenomena can be reversed or mitigated with effective antiretroviral therapy (ART), which blunts HIV replication and can reduce plasma levels of viremia to undetectable levels. Recent data from our laboratory have demonstrated fundamental differences between viremic and aviremic individuals with regard to the physiologic state of the resting CD4+ T-cell reservoir of HIV and the phenotype and function of T cells, B cells and natural killer (NK) cells. In terms of the CD4+ T-cell reservoir, resting cells in viremic versus aviremic individuals differentially express certain genes associated with HIV replication and are continually poised to express virus as a result of continual activation related to viremia; thus, true latency likely does not exist in these patients. We had previously reported that much greater stability exists in aviremic individuals, suggesting the presence of a truly latent reservoir of virus in this population. However, recent data indicate that the normal physiologic process of low-level immune activation in aviremic individuals sustained the low level turnover and propagation of the latent HIV reservoir. Previously, we have demonstrated that HIV-mediated hyperactivation induces the terminal differentiation of B cells. More recently, we have determined that certain B-cell genes are upregulated in HIVviremic individuals as compared with HIV-aviremic individuals. Many of these genes are associated with terminal B-cell differentiation and death by apoptosis. Recent data indicate that there is a balance between expression of survival and apoptotic genes in HIV-infected individuals that is impacted by the presence and level of viremia. In viremic individuals we also have characterized a population of aberrantly activated CD56NK cells that manifest lower-than-normal expression of Natural Cytotoxicity Receptors and a normal or increased expression of inhibitory NK receptors. This dichotomy is reflected in decreased cytotoxic function and decreased secretion of TNF-alpha and interferon-gamma. In addition, NK cells from viremic individuals express Fas on their surfaces at significantly increased levels, and are more susceptible to apoptosis upon exposure to sFASL. Furthermore, viremia impacts the NK cell-dendritic cell interactions that are critical to normal immune responsiveness. Taken together, our data indicate that HIV pathogenesis involves both direct and indirect effects of HIV and a relentless cycle of aberrant immune activation that drives the disease process in HIV-infected individuals. from 2005 International Meeting of The Institute of Human Virology Baltimore, USA, 29 August – 2 September 2005

After MHC-matched allografting, host-derived langerhans cells (LCs) persist in skin and cutaneous lymph nodes in the steady-state and are the targets of DLI-mediated alloresponse

The mechanisms that govern T cell-mediated alloresponses in the post-transplant setting, particularly T cell-dendritic cell (DC) interactions, are critical for developing strategies to augment their antitumor effects and limit toxicity such as GVHD. We hypothesize that kinetics of DC reconstitution and the number of host DCs persisting in various lymphoid tissues after alloBMT may differ and if characterized, may be relevant in guiding T cell alloresponses following transplant. To analyze DC reconstitution inthe MHC-matched setting, we used a B6Ly 5.2 (H2b ; CD45.1+)→ C3H.SW (H2b ; CD45.2+) model that differs in expression of the CD45 marker on host and donor hematopoietic tissues. We found that the donor to host DC turnover is rapid with near full conversion to donor DC chimerism in the spleen and mesenteric lymph nodes but not in the cutaneous lymph nodes (CLNs). The dominant residual host DC population in LNs is characterized by the low expression of CD8+ but high expression of DEC-205 and gp40 (Ep-CAM), the profile completely consistent with the phenotype of LCs. We reproducibly detected residual host-derived LCs in the chimeras CLNs for at least 6 months after alloBMT and found them to constitutively express an activated phenotype. Levels of expression of the costimulatory molecules, CD80, CD40, and especially CD86 on host-derived LCs was actually higher in comparison to donor-derived LCs. The skin origin of host-derived DCs in LNs was confirmed by analysis of CD11c+ that migrate out of ex vivo cultured epidermal sheets. Because the majority of the CD11c+ was of host origin, this suggests that alloresponse against minor histocompatibility antigens is not sufficient enough to cause LC replacement. The persistence of residual host LCs after alloBMT prompted us to determine whether they serve as the target of the DLI-mediated alloresponse. Administration of DLI 3 weeks after conditioning resulted in the decrease of residual host-derived LCs in the CLNs and recruitment of donor derived LCs to the skin. Our data suggest the following: (a) After myeloablative conditioning and transplantation of MHC-matched marrow, there is a rapid replacement of secondary lymphoid organs with donor marrow-derived DCs but that the significant amount of skin DCs are of host origin ; (b) during steady-state conditions after alloBMT, host-derived LCs bearing an activated phenotype are continuously present in the CLNs ; and (c) host-derived LCs are the targets of the DLI-mediated alloresponse.

T cell-dendritic cell interaction in vivo: random encounters favor development of long-lasting ties.

Understanding the complexity of the functional communication between cells composing the immune system is central to improving our capacity to manipulate it and conceive better strategies to combat microbial pathogens. So far, these studies have been based on immunohistochemistry of fixed tissues and in vitro attempts to reproduce functional connections between cells. The application of two-photon laser microscopy to the observation of viable immune cells in their natural environment where foreign antigens are carried to trigger an immune response opens a new era for these studies. They reveal exceptional properties of the locomotion of T cells that facilitate encounters with dendritic cells and the receipt of information that promotes T cell survival, death, or initiation of immune responses. These studies also complement in vitro observations addressing the importance of time of stimulation in determining T cell fates.

Natural Killer and Dendritic Cell Contact in Lesional Atopic Dermatitis Skin –Malassezia-Influenced Cell Interaction

The regulation of dendritic cells is far from fully understood. Interestingly, several recent reports have suggested a role for natural killer cells in affecting dendritic cell maturation and function upon direct contact between the cells. It is not known if this interaction takes place also in vivo, or if a potential interaction of natural killer cells and dendritic cells would be affected by allergen exposure of the dendritic cells. The yeast Malassezia can act as an allergen in atopic eczema/dermatitis syndrome, and induce maturation of dendritic cells. Our aims were to study the distribution of natural killer cells in the skin from atopic eczema/dermatitis syndrome patients with the emphasis on possible natural killer cell-dendritic cell interaction, and to assess whether the interaction of Malassezia with dendritic cells would affect subsequent interaction between dendritic cells and natural killer cells. A few scattered natural killer (CD56+/CD3-) cells were found in the dermis of healthy individuals and in nonlesional skin from atopic eczema/dermatitis syndrome patients. In lesional skin and in biopsies from Malassezia atopy-patch-test-positive skin, however, natural killer cells were differentially distributed and for the first time we could show close contact between natural killer cells and CD1a+ dendritic cells. Dendritic cells preincubated with Malassezia became less susceptible to natural-killer-cell-induced cell death, suggesting a direct effect imposed by Malassezia upon interaction of dendritic cells with natural killer cells. These findings indicate that natural killer cells and dendritic cells can interact in the skin and that Malassezia affects the interaction between natural killer cells and dendritic cells. Our data suggest that natural killer cells may play a role in regulating dendritic cells in atopic eczema/dermatitis syndrome.

Animated Immunity

Our current understanding of the complex cellular interactions required for immune responses has come largely from in vitro manipulation or from snapshots of events within fixed tissues. Three reports now describe real-time analysis of immune cell responses within living tissues (see the Perspective by von Adrian). Using two-photon technology to compare migration of T and B cells within organized lymphoid tissue, Miller et al. observed that T cells roam considerably further and at faster rates than B cells. This explorative behavior shifted toward focused clustering upon inclusion of antigen. Stoll et al. used modified single-photon confocal imaging to investigate interactions of naïve T cells with antigen on dendritic cell (DC) in lymph nodes. Extended periods of connection, with the formation of immune synapses and eventual departure of activated T cells, were observed in the presence of antigen-loaded DCs. Bousso et al. used two-photon imaging to study thymocyte interactions with thymic stromal cells in a reaggregated thymic organ culture. Recognition events that resulted in positive selection of thymocytes promoted thymocyte motility and increased the duration of thymocyte-thymic stromal cell contacts. U. H. von Andrian, T cell activation in six dimensions. Science 296 , 1815-1817 (2002). [Summary] [Full Text] M. J. Miller, S. H. Wei, I. Parker, M. D. Cahalan, Two-photon imaging of lymphocyte motility and antigen response in intact lymph node. Science 296 , 1869-1873 (2002). [Abstract] [Full Text] S. Stoll, J. Delon, T. M. Brotz, R. N. Germain, Dynamic imaging of T cell-dendritic cell interactions in lymph nodes. Science 296 , 1873-1876 (2002). [Abstract] [Full Text] P. Bousso, N. R. Bhakta, R. S. Lewis, E. Robey, Dynamics of thymocyte-stromal cell interactions visualized by two-photon microscopy. Science 296 , 1876-1880 (2002). [Abstract] [Full Text]

Dynamic imaging of T cell-dendritic cell interactions in lymph nodes.

T cell immune responses begin within organized lymphoid tissues. The pace, topology, and outcomes of the cellular interactions that underlie these responses have, so far, been inferred from static imaging of sectioned tissue or from studies of cultured cells. Here we report dynamic visualization of antigen-specific T cells interacting with dendritic cells within intact explanted lymph nodes. We observed immunological synapse formation and prolonged interactions between these two cell types, followed by the activation, dissociation, and rapid migration of T cells away from the antigenic stimulus. This high-resolution spatiotemporal analysis provides insight into the nature of cell interactions critical to early immune responses within lymphoid structures.

In vivo maturation and migration of dendritic cells.

The hallmark of immunity is antigen (Ag) recognition. From early life until death we face countless Ags; many are deleterious and come from the outside world. However, lymphocytes, the mediators of specific acquired immunity, are usually not exposed where foreign antigens are encountered. Thus a system must ferry these Ags from the periphery into inner tissues where lymphocytes comfortably reside or traffic. Clearly, translocating Ags from the periphery to the lymphoid niches is a pivotal function whereby the dendritic cell (DC) system initiates immune responses. DCs, however, are not passive Ag couriers; a dynamic process not fully understood is triggered by Ag deposition. Strategically poised at the boundaries between the inner and the outside world, in a way bridging innate and acquired immunity, DCs sample, trap, engulf, and digest Ags of very diverse origin, in what is called Ag processing. Antigenic fragments are then regurgitated, exposed at the cell surface through one of three molecular pathways [Major histocompatibility complex (MHC) CI and CII, and CD1)] responsible for an efficacious Ag presentation. Concomitantly, DC bear an arsenal of powerful costimulatory molecules [CD40; CD80; CD86; DC-specific/intercellular adhesion molecule type 3-grabbing, non-integrin (DC-SIGN)] and the potential to produce critical cytokines [chemokines, interleukin-12 (IL-12), etc.], thus ensuring the initiation and the fate of acquired immunity. The DC system is particularly efficient, not just translocating, but also transforming antigens sampled at the earlier local milieu into an immunologically accesible language, becoming an excellent reporter of the previous antigenic past, translating the conundrum posed by viruses, bacteria, proteins, etc., into T-cell receptor (TCR) ligands; a short-peptide vocabulary that T cells especially now understand. A highly dynamic process is thus triggered by encountering Ags; while these are carried and processed to be appropriately presented, DCs in turn experience a variety of changes: migratory, phenotypical, functional; all encompassed in the term maturation. Essentially, DC maturation means to change from an antigen-capturing to an antigen-presenting, T-cell-priming mode, a process whereby DCs convert antigens into efficacious immunogens, express the necessary cytokines and costimulatory molecules, thus appropriately initiating the specific, acquired clonal immunity.

CD40 ligand (CD154) enhances the Th1 and antibody responses to respiratory syncytial virus in the BALB/c mouse.

CD40 ligand (CD40L) is a cell surface costimulatory molecule expressed mainly by activated T cells. CD40L is critically important for T-B cell and T cell-dendritic cell interactions. CD40L expression promotes Th1 cytokine responses to protein Ags and is responsible for Ig isotype switching in B cells. Respiratory syncytial virus (RSV) is an important pathogen of young children and the elderly, which causes bronchiolitis and pneumonia. Studies of mice infected with RSV suggest that a Th2 cytokine response may be responsible for enhanced pulmonary disease. To investigate the effect CD40L has on RSV immunity, mice were infected simultaneously with RSV and either an empty control adenovirus vector or one expressing CD40L or were coimmunized with plasmid DNA vectors expressing CD40L and RSV F and/or G proteins and subsequently challenged with RSV. The kinetics of the intracellular and secreted cytokine responses, the cytotoxic T lymphocyte precursor frequency, NO levels in lung lavage, rates of virus clearance, and anti-RSV Ab titers were determined. These studies show that coincident expression of CD40L enhances the Th1 (IL-2 and IFN-gamma) cytokine responses, increases the expression of TNF-alpha and NO, accelerates virus clearance, and increases the anti-F and anti-G Ab responses. These data suggest that CD40L may have the adjuvant properties needed to optimize the safety and efficacy of RSV vaccines.