Basic mechanisms of DNA-raised antibody responses to intramuscular and gene gun immunizations

DNA-raised antibody (Ab) responses have been compared for the dependence on CD4+ and CD8+ cells, the longevity of functional antigen (Ag) expression, and the nature of the Ag-presenting cell after intramuscular (i.m.) and gene gun inoculations. A plasmid expressing the hemagglutinin (HA) glycoprotein of influenza virus was used for immunizations of BALB/c mice. Intramuscular and gene gun-raised Abs had similar dependencies on CD4+ and CD8+ cells but different temporal patterns of functional Ag expression. The two methods of DNA immunization also appeared to have different frequencies or types of Ag-presenting cells in the draining lymph nodes and spleen. For both methods of DNA delivery, Ab was independent of CD8+ cells but dependent on CD4+ cells. The CD4 dependence occurred at priming but not booster immunizations and resulted in a 1-month delay in the Ab response. Temporal T-cell transfers from TCR+/+ mice into immunized TCR-/- mice revealed the persistence of DNA-expressed Ag for up to 1 month after both i.m. and gene gun inoculations. For gene gun, but not i.m. immunizations, approximately 90% of the functional Ag expression was lost by 1 week, consistent with the sloughing of the epidermal target site. Despite similar titers of raised Ab, Ag-presenting dendritic cells could be detected in the draining lymph nodes and spleen of gene gun- but not i.m. DNA-immunized mice. In the gene gun-immunized mice, Ag-presenting dendritic cells appeared in the draining lymph nodes before the spleen.     

Protection against influenza A virus by memory CD8 T cells requires reactivation by bone marrow-derived dendritic cells

Influenza A virus is the causative agent of an acute inflammatory disease of the airway. Although Abs can prevent infection, disease and death can be prevented by T cell-mediated immunity. Recently, we showed that protection against lethal influenza A (PR8/34) virus infection is mediated by central memory CD8 T cells (T(CM)). In this study, using relB(-/-) mice we began to investigate the role of bone marrow (BM)-derived dendritic cells (DCs) in the mechanism of protection. We found that in the absence of functional DCs, memory CD8 T cells specific for the nucleoprotein epitope (NP(366-374)) fail to protect even after adoptive transfer into naive recipients. Through an analysis of Ag uptake, activation of memory CD8 T cells, and display of peptide/MHC complex by DCs in draining LNs and spleen early after virus infection, we established that lack of protection is associated with defective Ag presentation by BM-derived DCs and defective homing of memory T cells in the lymph nodes draining the airway tract. Collectively, the data suggest that protection against the influenza A virus requires that memory CD8 T cells be reactivated by Ag presented by BM-derived DCs in the lymph nodes draining the site of infection. They also imply that protection depends both on the characteristics of systemic adaptive immunity and on the coordinated interplay between systemic and local immunity.     

Cutting edge: a new approach to modeling early lung immunity in murine tuberculosis

In this study, we report a new approach that allows dissection of distinct pathways regulating induction of early adaptive immunity in response to Mycobacterium tuberculosis (Mtb). We used traceable murine dendritic cells (DCs) and macrophage populations to chart their migratory pattern in response to Mtb, and found that only DCs receiving inflammatory stimuli from Mtb up-regulated their expression of CCR7 and migrated specifically to the draining lymph nodes (LNs). Furthermore, these Mtb-modulated DCs initiated a Th1 response only in the draining LNs. Taken together, these results demonstrate that Mtb-induced modulation of DCs is critical for their migration to regional LNs and ensuing T cell priming.     

APCs in the anterior uveal tract do not migrate to draining lymph nodes

The migration of APCs from sites of infection and their maturation are critical elements in the generation of immune responses. However, the paths by which intraocular Ags migrate to draining lymph nodes are not known because the eye has limited lymphatic vessels. To date, only dendritic cells from the cornea and conjunctiva have been shown to emigrate. We demonstrate that phagocytic APCs in the anterior uveal tissues of the murine eye that ingest fluorescent latex beads do not migrate to regional lymph nodes. The beads are ingested in the uveal tract by cells expressing MHC class II, CD11c, or F4/80. Using intravital time-lapse videomicroscopy to monitor iris APC migration after anterior chamber injection of fluorescent Ag, fluorescently labeled APCs fail to move at multiple observation times, even in the presence of Ag and LPS. Whereas an as yet unidentified ocular nonphagocytic APC subset might migrate from the anterior uveal tissues, it is more probable that immune responses in the draining lymph nodes are engendered by soluble Ag escaping the eye through interstitial spaces. The inability of anterior uveal tissue APCs to migrate to lymph nodes may contribute to deviant immune responses that dominate after Ags are introduced into the anterior chamber.     

Impaired Humoral Immunity and Tolerance in K14-VEGFR-3-Ig Mice That Lack Dermal Lymphatic Drainage

Lymphatic vessels transport interstitial fluid, soluble Ag, and immune cells from peripheral tissues to lymph nodes (LNs), yet the contribution of peripheral lymphatic drainage to adaptive immunity remains poorly understood. We examined immune responses to dermal vaccination and contact hypersensitivity (CHS) challenge in K14-VEGFR-3-Ig mice, which lack dermal lymphatic capillaries and experience markedly depressed transport of solutes and dendritic cells from the skin to draining LNs. In response to dermal immunization, K14-VEGFR-3-Ig mice produced lower Ab titers. In contrast, although delayed, T cell responses were robust after 21 d, including high levels of Ag-specific CD8(+) T cells and production of IFN-γ, IL-4, and IL-10 upon restimulation. T cell-mediated CHS responses were strong in K14-VEGFR-3-Ig mice, but importantly, their ability to induce CHS tolerance in the skin was impaired. In addition, 1-y-old mice displayed multiple signs of autoimmunity. These data suggest that lymphatic drainage plays more important roles in regulating humoral immunity and peripheral tolerance than in effector T cell immunity.     

NKT cells inhibit antigen-specific effector CD8 T cell induction to skin viral proteins

We recently demonstrated that CD1d-restricted NKT cells resident in skin can inhibit CD8 T cell-mediated graft rejection of human papillomavirus E7-expressing skin through an IFN-γ-dependent mechanism. In this study, we examined the role of systemically derived NKT cells in regulating the rejection of skin grafts expressing viral proteins. In lymph nodes draining transplanted skin, Ag-specific CD8 T cell proliferation, cytokine production, and cytotoxic activity were impaired by NKT cells. NKT cell suppression was mediated via CD11c(+) dendritic cells. Inhibition of CD8 T cell function did not require Foxp3(+) regulatory T cells or NKT cell-secreted IFN-γ, IL-10, or IL-17. Thus, following skin grafting or immunization with human papillomavirus-E7 oncoprotein, NKT cells reduce the capacity of draining lymph node-resident APCs to cross-present Ag to CD8 T cell precursors, as evidenced by impaired expansion and differentiation to Ag-specific CD8 T effector cells. Therefore, in the context of viral Ag challenge in the skin, systemic NKT cells limit the capacity for effective priming of adaptive immunity.     

Langerhans cells are required for efficient presentation of topically applied hapten to T cells

Dendritic cells (DC) play a pivotal role in the control of T cell immunity due to their ability to stimulate naive T cells and direct effector function. Murine and human DC are composed of a number of phenotypically, and probably developmentally, distinct subsets, which may play unique roles in the initiation and regulation of T cell responses. The skin is populated by at least two subsets of DC: Langerhans cells (LC), which form a contiguous network throughout the epidermis, and dermal DC. LC have classically been thought vital to initiate T cell responses to cutaneous Ags. However, recent data have highlighted the importance of dermal DC in cutaneous immunity, and the requirement for LC has become unclear. To define the relative roles of LC and dermal DC, we and others generated mouse models in which LC were specifically depleted in vivo. Unexpectedly, these studies yielded conflicting data as to the role of LC in cutaneous contact hypersensitivity (CHS). Extending our initial finding, we demonstrate that topical Ag is inefficiently transported to draining lymph nodes in the absence of LC, resulting in suboptimal priming of T cells and reduced CHS. However, dermal DC may also prime cutaneous T cell responses, suggesting redundancy between the two different skin DC subsets in this model.     

Endogenous dendritic cells are required for amplification of T cell responses induced by dendritic cell vaccines in vivo

Dendritic cells (DCs) loaded in vitro with Ag are used as cellular vaccines to induce Ag-specific immunity. These cells are thought to be responsible for direct stimulation of Ag-specific T cells, which may subsequently mediate immunity. In this study, in transgenic mouse models with targeted MHC class II expression specifically on DCs, we show that the DC vaccine is responsible only for partial CD4(+) T cell activation, but to obtain optimal expansion of T cells in vivo, participation of endogenous (resident) DCs, but not endogenous B cells, is crucial. Transfer of Ag to endogenous DCs seems not to be mediated by simple peptide diffusion, but rather by DC-DC interaction in lymph nodes as demonstrated by histological analysis. In contrast, injection of apoptotic or necrotic DC vaccines does not induce T cell responses, but rather represents an immunological null event, which argues that viability of DC vaccines can be crucial for initial triggering of T cells. We propose that viable DCs from the DC vaccine must migrate to the draining lymph nodes and initiate a T cell response, which thereafter requires endogenous DCs that present transferred Ag in order induce optimal T cell expansion. These results are of specific importance with regard to the applicability of DC vaccinations in tumor patients, where the function of endogenous DCs is suppressed by either tumors or chemotherapy.     

The duration of signaling through CD40 directs biological ability of dendritic cells to induce antitumor immunity

Although it has been demonstrated that the functions of dendritic cells (DCs), including Ag capture, Ag presentation, and migratory activity, change dynamically with their maturation, the most appropriate conditioning of DCs for anticancer immunotherapy is still unclear. The help signal is one of the most potent stimuli for DC maturation and is provided by the interaction of CD40 expressed on DCs with CD40 ligand on CD4(+) T cells. To elucidate the appropriate conditioning of DCs for anticancer immunotherapy, we examined the biological activity of DCs stimulated with immobilized anti-CD40 Ab. DCs stimulated for 3 h (3h-DCs) still showed an immature phenotype, but exhibited augmented migration toward secondary lymphoid tissues. Subcutaneous injection of 3h-DCs facilitated priming of T cells, which could mediate potent antitumor therapeutic efficacy, in draining lymph nodes and successfully induced protective immunity. In contrast, 24h-DCs showed a mature phenotype with good Ag presentation ability to induce cell killing by adoptively transferred CD8(+) T cells when injected at tumor sites; however, they showed no migratory activity and were unable to induce protective immunity when injected s.c. This is the first report that functionally distinct DCs, either for the priming phase or for the effector phase, could be obtained by conditioning with CD40 stimulation and that the duration of stimulation determines the biological outcome. The usage of DCs conditioned for the priming phase might provide significant advantages in anticancer immunotherapy.     

CD64 expression distinguishes monocyte-derived and conventional dendritic cells and reveals their distinct role during intramuscular immunization

Although most vaccines are administered i.m., little is known about the dendritic cells (DCs) that are present within skeletal muscles. In this article, we show that expression of CD64, the high-affinity IgG receptor FcγRI, distinguishes conventional DCs from monocyte-derived DCs (Mo-DCs). By using such a discriminatory marker, we defined the distinct DC subsets that reside in skeletal muscles and identified their migratory counterparts in draining lymph nodes (LNs). We further used this capability to analyze the functional specialization that exists among muscle DCs. After i.m. administration of Ag adsorbed to alum, we showed that alum-injected muscles contained large numbers of conventional DCs that belong to the CD8α(+)- and CD11b(+)-type DCs. Both conventional DC types were capable of capturing Ag and of migrating to draining LNs, where they efficiently activated naive T cells. In alum-injected muscles, Mo-DCs were as numerous as conventional DCs, but only a small fraction migrated to draining LNs. Therefore, alum by itself poorly induces Mo-DCs to migrate to draining LNs. We showed that addition of small amounts of LPS to alum enhanced Mo-DC migration. Considering that migratory Mo-DCs had, on a per cell basis, a higher capacity to induce IFN-γ-producing T cells than conventional DCs, the addition of LPS to alum enhanced the overall immunogenicity of Ags presented by muscle-derived DCs. Therefore, a full understanding of the role of adjuvants during i.m. vaccination needs to take into account the heterogeneous migratory and functional behavior of muscle DCs and Mo-DCs revealed in this study.     

Analysis of Pulmonary Dendritic Cell Maturation and Migration during Allergic Airway Inflammation

Dendritic cells (DCs) are the key players involved in initiation of adaptive immune response by activating antigen-specific T cells. DCs are present in peripheral tissues in steady state; however in response to antigen stimulation, DCs take up the antigen and rapidly migrate to the draining lymph nodes where they initiate T cell response against the antigen^1,2. Additionally, DCs also play a key role in initiating autoimmune as well as allergic immune response³.DCs play an essential role in both initiation of immune response and induction of tolerance in the setting of lung environment⁴. Lung environment is largely tolerogenic, owing to the exposure to vast array of environmental antigens⁵. However, in some individuals there is a break in tolerance, which leads to induction of allergy and asthma. In this study, we describe a strategy, which can be used to monitor airway DC maturation and migration in response to the antigen used for sensitization. The measurement of airway DC maturation and migration allows for assessment of the kinetics of immune response during airway allergic inflammation and also assists in understanding the magnitude of the subsequent immune response along with the underlying mechanisms.Our strategy is based on the use of ovalbumin as a sensitizing agent. Ovalbumin-induced allergic asthma is a widely used model to reproduce the airway eosinophilia, pulmonary inflammation and elevated IgE levels found during asthma^6,7. After sensitization, mice are challenged by intranasal delivery of FITC labeled ovalbumin, which allows for specific labeling of airway DCs which uptake ovalbumin. Next, using several DC specific markers, we can assess the maturation of these DCs and can also assess their migration to the draining lymph nodes by employing flow cytometry.     

Cutaneous antigen priming via gene gun leads to skin-selective Th2 immune-inflammatory responses

It is becoming increasingly evident that the compartmentalization of immune responses is governed, in part, by tissue-selective homing instructions imprinted during T cell differentiation. In the context of allergic diseases, the fact that "disease" primarily manifests in particular tissue sites, despite pervasive allergen exposure, supports this notion. However, whether the original site of Ag exposure distinctly privileges memory Th2 immune-inflammatory responses to the same site, while sparing remote tissue compartments, remains to be fully investigated. We examined whether skin-targeted delivery of plasmid DNA encoding OVA via gene-gun technology in mice could generate allergic sensitization and give rise to Th2 effector responses in the skin as well as in the lung upon subsequent Ag encounter. Our data show that cutaneous Ag priming induced OVA-specific serum IgE and IgG1, robust Th2-cytokine production, and late-phase cutaneous responses and systemic anaphylactic shock upon skin and systemic Ag recall, respectively. However, repeated respiratory exposure to aerosolized OVA failed to instigate airway inflammatory responses in cutaneous Ag-primed mice, but not in mice initially sensitized to OVA via the respiratory mucosa. Importantly, these contrasting airway memory responses correlated with the occurrence of Th2 differentiation events at anatomically separate sites: indeed cutaneous Ag priming resulted in Ag-specific proliferative responses and Th2 differentiation in skin-, but not thoracic-, draining lymph nodes. These data indicate that Ag exposure to the skin leads to Th2 differentiation within skin-draining lymph nodes and subsequent Th2 immunity that is selectively manifested in the skin.     

Activation, differentiation, and migration of naive virus-specific CD8+ T cells during pulmonary influenza virus infection

The low precursor frequency of individual virus-specific CD8(+) T cells in a naive host makes the early events of CD8(+) T cell activation, proliferation, and differentiation in response to viral infection a challenge to identify. We have therefore examined the response of naive CD8(+) T cells to pulmonary influenza virus infection with a murine adoptive transfer model using hemagglutinin-specific TCR transgenic CD8(+) T cells. Initial activation of CD8(+) T cells occurs during the first 3 days postinfection exclusively within the draining lymph nodes. Acquisition of CTL effector functions, including effector cytokine and granule-associated protease expression, occurs in the draining lymph nodes and differentially correlates with cell division. Division of activated CD8(+) T cells within the draining lymph nodes occurs in an asynchronous manner between days 3 and 4 postinfection. Despite the presence of Ag for several days within the draining lymph nodes, dividing T cells do not appear to maintain contact with residual Ag. After multiple cell divisions, CD8(+) T cells exit the draining lymph nodes and migrate to the infected lung. Activated CD8(+) T cells also disseminate throughout lymphoid tissue including the spleen and distal lymph nodes following their emigration from draining lymph nodes. These results demonstrate an important role for draining lymph nodes in orchestrating T cell responses during a local infection of a discrete organ to generate effector CD8(+) T cells capable of responding to infection and seeding peripheral lymphoid tissues.     

Dendritic cells in the induction of protective and nonprotective anticryptococcal cell-mediated immune responses

Dendritic cells (DC) can be divided into three subsets, Langerhans cells, myeloid DC (MDC), and lymphoid DC (LDC), based upon phenotypic and functional differences. We hypothesized that different DC subsets are associated with the development of protective vs nonprotective cell-mediated immune (CMI) responses against the fungal pathogen, Cryptococcus neoformans. To test this, mice were immunized with protective and/or nonprotective immunogens, and DC subsets in draining lymph nodes were assessed by flow cytometry. The protective immunogen (cryptococcal culture filtrate Ag-CFA), in contrast to the nonprotective immunogen (heat-killed cryptococci-CFA), the nonprotective immunogen mixed with the protective immunogen (cryptococcal culture filtrate Ag + heat-killed cryptococci-CFA), or controls, stimulated significant increases in total leukocytes, Langerhans cells, MDC, LDC, and activated CD4+ T cells in draining lymph nodes. The protective immune response resulted in significantly increased levels of anticryptococcal delayed-type hypersensitivity reactivity and activated CD4+ T cells at the delayed-type hypersensitivity reaction site. Draining lymph node LDC:MDC ratios induced by the protective immunogen were significantly lower than the ratios induced by either immunization in which the nonprotective immunogen was present. In contrast, mice given the nonprotective immunogen had LDC:MDC ratios similar to those of naive mice. Our data indicate that lymph node Langerhans cells and MDC are APC needed for induction of the protective response. The predominance of LDC in mice undergoing nonprotective responses suggests that lymph node LDC, like splenic LDC, are negative regulators of CMI responses. In addition to showing DC subsets associated with functional differences, our data suggest that the LDC:MDC balance, which can be modulated by the Ag, determines whether protective or nonprotective anticryptococcal CMI responses develop.     

Inhalation tolerance is induced selectively in thoracic lymph nodes but executed pervasively at distant mucosal and nonmucosal tissues

Under immunogenic conditions, both the site of initial Ag exposure and consequent T cell priming in specific draining lymph nodes (LNs) imprint the ensuing immune response with lasting tissue-selective tropism. With respect to immune tolerance, whether the site of tolerance induction leads to compartmentalized or, alternatively, pervasive tolerance has not been formally investigated. Using a murine model of inhalation tolerance, we investigated whether the induction of respiratory mucosal tolerance precludes the development of de novo Th2 sensitization upon subsequent exposure to the same Ag at distant mucosal (gut) and nonmucosal (cutaneous) sites. By tracking the proliferation of CFSE-labeled OVA-TCR transgenic CD4(+) T cells upon OVA inhalation in vivo, we defined the site of tolerance induction to be restricted to the thoracic LNs. Expectedly, inhalation tolerance prevented de novo Th2 sensitization upon subsequent exposure to the same Ag at the same site. Importantly, although gut- and skin-draining LNs were not used during tolerance induction, de novo Ag-specific proliferation and Th2 differentiation in these LNs, as well as memory/effector Th2 responses in the gut (allergic diarrhea) and skin (late-phase cutaneous responses) were inhibited upon immunogenic challenge to the same Ag. Interestingly, this pervasive tolerogenic phenotype was not associated with the presence of suppressive activity throughout the lymphatics; indeed, potent suppressive activity was detected solely in the spleen. These data indicate that while inhalation tolerance is selectively induced in local thoracic LNs, its tolerogenic activity resides systemically and leads to pervasive immune tolerance in distant mucosal and nonmucosal sites.     

CD23+ CD21(high) CD1d(high) B cells in inflamed lymph nodes are a locally differentiated population with increased antigen capture and activation potential

CD23(+)CD21(high)CD1d(high) B cells in inflamed nodes (Bin cells) accumulate in the lymph nodes (LNs) draining inflamed joints of the TNF-α-transgenic mouse model of rheumatoid arthritis and are primarily involved in the significant histological and functional LN alterations that accompany disease exacerbation in this strain. In this study, we investigate the origin and function of Bin cells. We show that adoptively transferred GFP(+) sorted mature follicular B (FoB) cells home preferentially to inflamed LNs of TNF-α-transgenic mice where they rapidly differentiate into Bin cells, with a close correlation with the endogenous Bin fraction. Bin cells are also induced in wild-type LNs after immunization with T-dependent Ags and display a germinal center phenotype at higher rates compared with FoB cells. Furthermore, we show that Bin cells can capture and process Ag-immune complexes in a CD21-dependent manner more efficiently than can FoB cells, and they express greater levels of MHC class II and costimulatory Ags CD80 and CD86. We propose that Bin cells are a previously unrecognized inflammation-induced B cell population with increased Ag capture and activation potential, which may facilitate normal immune responses but may contribute to autoimmunity when chronic inflammation causes their accumulation and persistence in affected LNs.     

Inflammation, lymphatic function, and dendritic cell migration

The lymphatic system is not only essential for maintenance of normal fluid balance, but also for proper immunologic function by providing an extensive network of vessels, important for cell trafficking and antigen delivery, as well as an exclusive environment, the lymph node (LN), where antigen-presenting cells (APCs) and lymphocytes can encounter and interact. Among APCs, dendritic cells (DCs) have a remarkable capacity to traffic from peripheral tissues to the draining LN, which is critical for execution of their functions. To reach the LN, DCs must migrate towards and enter lymphatic vessels. Here, the authors review what is known about the factors that drive this process. They touch particularly on the topic of how DC migration is affected by inflammation and discuss this in the context of lymphatic function. Traditionally, inflammatory mediators are regarded to support DC migration to LNs because they induce molecules on DCs known to guide them to lymphatics. The authors recently showed that inflammatory signals present in a strong vaccine adjuvant induce swelling in LNs accompanied by lymphangiogenesis in the draining LN and radius of peripheral tissue. These increased lymphatics, at least for several days, lead to a more robust migration of DCs. However, the density of lymphatic vessels can become overly extended and/or their function impaired as observed during lymphedema and various chronic inflammatory reactions. Diseases characterized by chronic inflammation often present with impaired DC migration and adaptive immunity. Gaining a better understanding of how lymphatic vessel function may impact adaptive immunity by, for example, altering DC migration will benefit clinical research aiming to manipulate immune responses and manage chronic inflammatory diseases.     

Involvement of aquaporin-7 in the cutaneous primary immune response through modulation of antigen uptake and migration in dendritic cells

Dendritic cells (DCs) have the ability to present antigen and play a critical role in the induction of the acquired immune response. Skin DCs uptake antigen and subsequently migrate to regional draining lymph nodes (LNs), where they activate naive T cells. Here we show that the water/glycerol channel protein aquaporin 7 (AQP7) is expressed on epidermal and dermal DCs and involved in the initiation of primary immune responses. AQP7-deficient DCs showed a decreased cellular uptake of low-molecular-mass compounds (fluorescein isothiocyanate and Lucifer yellow) and high-molecular-mass substances (ovalbumin and dextran), suggesting that AQP7 is involved in antigen uptake. AQP7-deficient DCs also exhibited reduced chemokine-dependent cell migration in comparison to wild-type DCs. Consistent with these in vitro results, AQP7-deficient mice demonstrated a reduced accumulation of antigen-retaining DCs in the LNs after antigen application to the skin, which could be attributed to decreased antigen uptake and migration. Coincidentally, AQP7-deficient mice had impaired antigen-induced sensitization in a contact hypersensitivity model. These observations suggested that AQP7 in skin DCs is primarily involved in antigen uptake and in the subsequent migration of DCs and is responsible for antigen presentation and the promotion of downstream immune responses.     

CD4+ T cells can protect APC from CTL-mediated elimination

Professional APC play a central role in generating antiviral CD8(+) CTL immunity. However, the fate of such APC following interaction with these same CTL remains poorly understood. We have shown previously that prolonged Ag presentation persists in the presence of a strong CTL response following HSV infection. In this study, we examined the mechanism of survival of APC in vivo when presenting an immunodominant determinant from HSV. We show that transferred peptide-labeled dendritic cells were eliminated from draining lymph nodes in the presence of HSV-specific CTL. Maturation of dendritic cells with LPS or anti-CD40 before injection protected against CTL lysis in vivo. Furthermore, endogenous APC could be eliminated from draining lymph nodes early after HSV infection by adoptive transfer of HSV-specific CTL, yet the cotransfer of significant virus-specific CD4(+) T cell help promoted prolonged Ag presentation. This suggests that Th cells may assist in prolonging class I-restricted Ag presentation, potentially enhancing CTL recruitment and allowing more efficient T cell priming.     

Novel function of IFN-gamma: negative regulation of dendritic cell migration and T cell priming

IFN-gamma is considered to be a Th1 cytokine with immunomodulatory effects on a variety of immune cells. In this study, we determined whether dendritic cell (DC) function was aberrant in IFN-gamma knockout (GKO) mice. The results demonstrated that IFN-gamma deficiency did not interfere with bone marrow-derived DC development and maturation in vitro. However, functional analysis showed that bone marrow-derived DC from GKO mice had altered cytokine secretion, allostimulatory and Ag presentation capacity, chemokine receptor expression, and in vitro chemotaxis. LPS induced the recruitment of DC from different organs into the spleen; epicutaneously sensitized DC with hapten (FITC) accumulated in the draining lymph nodes and CD11c(+) DC levels in the draining lymph nodes from autoantigen (interphotoreceptor retinoid-binding protein) immunized mice were enhanced in GKO mice as compared with wild-type mice. After treatment of GKO mice with i.p. IFN-gamma injection restored IFN-gamma levels in vivo, DC migration decreased in response to LPS or FITC. IFN-gamma altered the adaptive immune responses in vivo, since T cell priming and IL-2 production were increased in interphotoreceptor retinoid-binding protein-immunized GKO mice. Furthermore, in IFN-gamma-treated GKO mice, experimental autoimmune uveitis score enhancement and T cell activation were eliminated. Taken together, IFN-gamma appears to play a negative regulatory role on in vivo DC function, resulting in suppression of Ag-specific T cell priming.