Fc gamma RIIB regulates nasal and oral tolerance: a role for dendritic cells

Mucosal tolerance prevents the body from eliciting productive immune responses against harmless Ags that enter the body via the mucosae, and is mediated by the induction of regulatory T cells that differentiate in the mucosa-draining lymph nodes (LN) under defined conditions of Ag presentation. In this study, we show that mice deficient in FcgammaRIIB failed to develop mucosal tolerance to OVA, and demonstrate in vitro and in vivo a critical role for this receptor in modulating the Ag-presenting capacity of dendritic cells (DC). In vitro it was shown that absence of FcgammaRIIB under tolerogenic conditions led to increased IgG-induced release of inflammatory cytokines such as MCP-1, TNF-alpha, and IL-6 by bone marrow-derived DC, and increased their expression of costimulatory molecules, resulting in an altered immunogenic T cell response associated with increased IL-2 and IFN-gamma secretion. In vivo we could show enhanced LN-DC activation and increased numbers of Ag-specific IFN-gamma-producing T cells when FcgammaRIIB(-/-) mice were treated with OVA via the nasal mucosa, inferring that DC modulation by FcgammaRIIB directed the phenotype of the T cell response. Adoptive transfer of CD4(+) T cells from the spleen of FcgammaRIIB(-/-) mice to naive acceptor mice demonstrated that OVA-responding T cells failed to differentiate into regulatory T cells, explaining the lack of tolerance in these mice. Our findings demonstrate that signaling via FcgammaRIIB on DC, initiated by local IgG in the mucosa-draining LN, down-regulates DC activation induced by nasally applied Ag, resulting in those defined conditions of Ag presentation that lead to Tr induction and tolerance.     

A novel adenovirus expressing Flt3 ligand enhances mucosal immunity by inducing mature nasopharyngeal-associated lymphoreticular tissue dendritic cell migration

Previously, we showed that nasal administration of a naked cDNA plasmid expressing Flt3 ligand (FL) cDNA (pFL) enhanced CD4(+) Th2-type, cytokine-mediated mucosal immunity and increased lymphoid-type dendritic cell (DC) numbers. In this study, we investigated whether targeting nasopharyngeal-associated lymphoreticular tissue (NALT) DCs by a different delivery mode of FL, i.e., an adenovirus (Ad) serotype 5 vector expressing FL (Ad-FL), would provide Ag-specific humoral and cell-mediated mucosal immunity. Nasal immunization of mice with OVA plus Ad-FL as mucosal adjuvant elicited high levels of OVA-specific Ab responses in external secretions and plasma as well as significant levels of OVA-specific CD4(+) T cell proliferative responses and OVA-induced IFN-gamma and IL-4 production in NALT, cervical lymph nodes, and spleen. We also observed higher levels of OVA-specific CTL responses in the spleen and cervical lymph nodes of mice given nasal OVA plus Ad-FL than in mice receiving OVA plus control Ad. Notably, the number of CD11b(+)CD11c(+) DCs expressing high levels of costimulatory molecules was preferentially increased. These DCs migrated from the NALT to mucosal effector lymphoid tissues. Taken together, these results suggest that the use of Ad-FL as a nasal adjuvant preferentially induces mature-type NALT CD11b(+)CD11c(+) DCs that migrate to effector sites for subsequent CD4(+) Th1- and Th2-type cytokine-mediated, Ag-specific Ab and CTL responses.     

Influence of mucosal adjuvants on antigen passage and CD4+ T cell activation during the primary response to airborne allergen

Ag delivery via the nasal route typically induces tolerance or fails to polarize CD4+ T cell responses unless an adjuvant is provided. To better understand this process, we assessed the effects of two mucosal adjuvants, Escherichia coli LPS and cholera toxin (CT), on Ag passage and T cell activation in the draining lymph nodes (DLN) of BALB/c mice following per nasal administration of the model protein allergen, OVA. We found a range of cell types acquired small amounts of fluorescent OVA in the DLN 4 h after per nasal administration. However, this early uptake was eclipsed by a wave of OVA+CD8alpha(low) dendritic cells that accumulated in the DLN over the next 20 h to become the dominant OVA-processing and -presenting population. Both LPS and CT stimulated increases in CD80 and CD86 expression on OVA+CD8alpha(low) DC. LPS also increased the number of OVA+CD8alpha(low) dendritic cells accumulating in the DLN. When the primary T cell response was examined after adoptive transfer of CD4+ T cells from DO11.10 mice, CT and LPS stimulated surprisingly similar effects on T cell activation and proliferation, IL-4 and IFN-gamma priming, and memory T cell production. Despite these similarities, T cell recipients immunized with CT, but not LPS, developed lung eosinophilia upon secondary OVA challenge. Thus, we found no bias within the DLN in Ag handling or the primary T cell response associated with the eventual Th2 polarization induced by CT, and suggest that additional tissue-specific factors influence the development of allergic disease in the airways.     

Dendritic cell-mediated induction of mucosal cytotoxic responses following intravaginal immunization with the nontoxic B subunit of cholera toxin

The use of the nontoxic B subunit of cholera toxin (CTB) as mucosal adjuvant and carrier-delivery system for inducing secretory Ab responses has been documented previously with different soluble Ags. In this study, we have evaluated this approach for inducing CTL responses against a prototype Ag, OVA, in the female genital mucosa. We report here the ability of an immunogen comprised of CTB conjugated to OVA (CTB-OVA) given by intravaginal (ivag) route to induce genital OVA-specific CTLs in mice. Using adoptive transfer models, we demonstrate that ivag application of CTB-OVA activates OVA-specific IFN-gamma-producing CD4 and CD8 T cells in draining lymph nodes (DLN). Moreover, ivag CTB induces an expansion of IFN-gamma-secreting CD8+ T cells in DLN and genital mucosa and promotes Ab responses to OVA. In contrast, ivag administration of OVA alone or coadministered with CTB failed to induce such responses. Importantly, we demonstrate that ivag CTB-OVA generates OVA-specific CTLs in DLN and the genital mucosa. Furthermore, genital CD11b+ CD11c+ dendritic cells (DCs), but not CD8+ CD11c+ or CD11c- APCs, present MHC class I epitopes acquired after ivag CTB-OVA, suggesting a critical role of this DC subset in the priming of genital CTLs. Inhibition studies indicate that the presentation of OVA MHC class I epitopes by DCs conditioned with CTB-OVA involves a proteasome-dependent and chloroquine-sensitive mechanism. These results demonstrate that CTB is an efficient adjuvant-delivery system for DC-mediated induction of genital CTL responses and may have implications for the design of vaccines against sexually transmitted infections.     

Plasmacytoid dendritic cells do not migrate in intestinal or hepatic lymph

Plasmacytoid dendritic cells (pDCs) recognize pathogen-associated molecules, particularly viral, and represent an important mechanism in innate defense. They may however, also have roles in steady-state tolerogenic responses at mucosal sites. pDCs can be isolated from blood, mucosa, and lymph nodes (LNs). Although pDCs can express peripherally derived Ags in LNs and at mucosal sites, it is not clear whether pDCs actually migrate from the periphery in lymph or whether LN pDCs acquire Ags by other mechanisms. To determine whether pDCs migrate in lymph, intestine or liver-draining LNs were removed and thoracic duct leukocytes (TDLs) were collected. TDLs expressing MHC-II and CD45R, but not TCRalphabeta or CD45RA, were then analyzed. These enriched TDLs neither transcribe type I IFNs nor secrete inflammatory cytokines in response to viral stimuli in vitro or after a TLR7/8 stimulus in vivo. In addition, these TDLs do not express CD5, CD90, CD200, or Siglec-H, but do express Ig, and therefore represent B cells, despite their lack of CD45RA expression. Intestinal and hepatic lymph are hence devoid of bona fide pDCs under both steady-state conditions and after TLR7/8 stimulation. This shows that any role for pDCs in Ag-specific T cell activation or tolerance must differ from the roles of classical dendritic cells, because it cannot result from peripheral Ag capture, followed by migration of pDCs via lymph to the LN.     

Synchronization of dendritic cell activation and antigen exposure is required for the induction of Th1/Th17 responses

The dendritic cell (DC) targeting/activation patterns required to elicit Th1/Th17 responses remain undefined. One postulated requirement was that of a physical linkage between Ags and immunomodulators. Accordingly, the separate same-site administration of Ag85B-ESAT-6 (hybrid-1 protein; H1), a mycobacterial fusion Ag, and the CAF01 liposome-based adjuvant induced similar Ab and weak Th2 responses as those of coformulated H1/CAF01 but failed to elicit Th1/Th17 responses. Yet, this separate same-site injection generated the same type and number of activated Ag(+)/adjuvant(+) DCs in the draining lymph nodes (LN) as that of protective H1/CAF01 immunization. Thus, targeting/activating the same DC population by Ag and adjuvant is not sufficient to elicit Th1/Th17 responses. To identify the determinants of Th1/Th17 adjuvanticity, in vivo tracking experiments using fluorescently labeled Ag and adjuvant identified that a separate same-site administration elicits an additional early Ag(+)/adjuvant(-) DC population with a nonactivated phenotype, resulting from the earlier targeting of LN DCs by H1 than by CAF01 molecules. This asynchronous targeting pattern was mimicked by the injection of free H1 prior to or with, but not after, H1/CAF01 or H1/CpG/ aluminum hydroxide immunization. The injection of soluble OVA similarly prevented the induction of Th1 responses by OVA/CAF01. Using adoptively transferred OT-2 cells, we show that the Ag targeting of LN DCs prior to their activation generates nonactivated Ag-pulsed DCs that recruit Ag-specific T cells, trigger their initial proliferation, but interfere with Th1 induction in a dose-dependent manner. Thus, the synchronization of DC targeting and activation is a critical determinant for Th1/Th17 adjuvanticity.     

The extra domain A from fibronectin targets antigens to TLR4-expressing cells and induces cytotoxic T cell responses in vivo

Vaccination strategies based on the in vivo targeting of Ags to dendritic cells (DCs) are needed to improve the induction of specific T cell immunity against tumors and infectious agents. In this study, we have used a recombinant protein encompassing the extra domain A from fibronectin (EDA), an endogenous ligand for TLR4, to deliver Ags to TLR4-expressing DC. The purified EDA protein was shown to bind to TLR4-expressing HEK293 cells and to activate the TLR4 signaling pathway. EDA also stimulated the production by DC of proinflammatory cytokines such as IL-12 or TNF-alpha and induced their maturation in vitro and in vivo. A fusion protein between EDA and a cytotoxic T cell epitope from OVA efficiently presented this epitope to specific T cells and induced the in vivo activation of a strong and specific CTL response. Moreover, a fusion protein containing EDA and the full OVA also improved OVA presentation by DC and induced CTL responses in vivo. These EDA recombinant proteins protected mice from a challenge with tumor cells expressing OVA. These results strongly suggest that the fibronectin extra domain A may serve as a suitable Ag carrier for the development of antiviral or antitumoral vaccines.     

Cytokine requirements for induction of systemic and mucosal CTL after nasal immunization.

Cholera toxin (CT) is frequently used as an experimental adjuvant intranasally for the induction of systemic and mucosal immunity. However, CT is highly reactogenic and not approved for use in humans. To define the cytokine requirements for the nasal activation of the systemic and mucosal immune system, and to design new adjuvants with efficacy similar to CT, we defined the cytokines that were able to replace CT as a nasal adjuvant for the induction of CTL. BALB/c mice were nasally immunized with an HIV immunogen that contains an MHC class I-restricted CTL epitope +/- cytokines and tested for HIV-specific immune responses. We found that combinations of IL-1alpha plus IL-18, IL-1alpha plus IL-12, and IL-1alpha plus IL-12 plus GM-CSF each induced optimal splenocyte anti-HIV CTL responses in immunized mice (range 60-71% peptide-specific (51)Cr release). Peak H-2D(d)-peptide tetramer-binding T cell responses induced by cytokine combinations were up to 5.5% of CD8(+) PBMC. Nasal immunization with HIV immunogen and IL-1alpha, IL-12, and GM-CSF also induced Ag-specific IFN-gamma-secreting cells in the draining cervical lymph node and the lung. The use of IL-1alpha, IL-12, and GM-CSF as nasal adjuvants was associated with an increased expression of MHC class II and B7.1 on nonlymphocytes within the nasal-associated lymphoid tissue/nasal mucosa. Thus, IL-1alpha, IL-12, IL-18, and GM-CSF are critical cytokines for the induction of systemic and mucosal CTL after nasal immunization. Moreover, these cytokines may serve as effective adjuvants for nasal vaccine delivery.     

The kidney-renal lymph node-system contributes to cross-tolerance against innocuous circulating antigen

Soluble Ags devoid of inflammatory stimuli, derived for example from self-serum or food proteins, induce T cell tolerance, predominantly in the spleen. In this study, we describe an additional role of the kidney-renal LN (rLN) system in tolerogenic presentation of circulating soluble Ags. Protein below albumin molecular mass constitutively passed the kidney glomerular filter and was concentrated in the tubular compartment. Enriched filterable Ag was endocytosed by kidney dendritic cells (kDCs). Simultaneously, it was transported cell independently within 2 min to DCs resident in rLNs. These DC phenotypically differed from kDCs carrying filterable Ag, and used a distinct mechanism, mannose receptor-mediated endocytosis, to internalize Ag. They activated specific CD8+ T cells, which subsequently proliferated without producing effector cytokines or developing cytotoxic activity, showed a curtailed lifespan and signs of apoptosis. Such T cell tolerization was independent of steady-state migratory kDC, because it occurred also when nephrectomy was performed soon after Ag injection. These findings demonstrate that the kidney dispatches concentrated blood-borne Ags to the rLNs, where they are captured by resident DCs, resulting in CD8+ T cell cross-tolerance. This mechanism may contribute to avoiding immunity against innocuous circulating protein Ags below albumin size.     

Notch-ligand expression by NALT dendritic cells regulates mucosal Th1- and Th2-type responses

Our previous studies showed that an adenovirus (Ad) serotype 5 vector expressing Flt3 ligand (Ad-FL) as nasal adjuvant activates CD11c(+) dendritic cells (DCs) for the enhancement of antigen (Ag)-specific IgA antibody (Ab) responses. In this study, we examined the molecular mechanism for activation of CD11c(+) DCs and their roles in induction of Ag-specific Th1- and Th2-cell responses. Ad-FL activated CD11c(+) DCs expressed increased levels of the Notch ligand (L)-expression and specific mRNA. When CD11c(+) DCs from various mucosal and systemic lymphoid tissues of mice given nasal OVA plus Ad-FL were cultured with CD4(+) T cells isolated from non-immunized OVA TCR-transgenic (OT II) mice, significantly increased levels of T cell proliferative responses were noted. Furthermore, Ad-FL activated DCs induced IFN-γ, IL-2 and IL-4 producing CD4(+) T cells. Of importance, these APC functions by Ad-FL activated DCs were down-regulated by blocking Notch-Notch-L pathway. These results show that Ad-FL induces CD11c(+) DCs to the express Notch-ligands and these activated DCs regulate the induction of Ag-specific Th1- and Th2-type cytokine responses.     

Generation of mucosal dendritic cells from bone marrow reveals a critical role of retinoic acid

It is unknown how dendritic cells (DCs) become specialized as mucosal DCs and maintain intestinal homeostasis. We report that a subset of bone marrow cells freshly isolated from C57BL/6 mice express the retinoic acid (RA)-synthesizing enzyme aldehyde dehydrogenase family 1, subfamily A2 (ALDH1a2) and are capable of providing RA to DC precursors in the bone marrow microenvironment. RA induced bone marrow-derived DCs to express CCR9 and ALDH1a2 and conferred upon them mucosal DC functions, including induction of Foxp3(+) regulatory T cells, IgA-secreting B cells, and gut-homing molecules. This response of DCs to RA was dependent on a narrow time window and stringent dose effect. RA promoted bone marrow-derived DC production of bioactive TGF-β by inhibiting suppressor of cytokine signaling 3 expression and thereby enhancing STAT3 activation. These RA effects were evident in vivo, in that mucosal DCs from vitamin A-deficient mice had reduced mucosal DC function, namely failure to induce Foxp3(+) regulatory T cells. Furthermore, MyD88 signaling enhanced RA-educated DC ALDH1a2 expression and was required for optimal TGF-β production. These data indicate that RA plays a critical role in the generation of mucosal DCs from bone marrow and in their functional activity.     

Cytotoxic dendritic cells generated from cancer patients

Known for years as professional APCs, dendritic cells (DCs) are also endowed with tumoricidal activity. This dual role of DC as killers and messengers may have important implications for tumor immunotherapy. However, the tumoricidal activity of DCs has mainly been investigated in animal models. Cancer cells inhibit antitumor immune responses using numerous mechanisms, including the induction of immunosuppressive/ tolerogenic DCs that have lost their ability to present Ags in an immunogenic manner. In this study, we evaluated the possibility of generating tumor killer DCs from patients with advanced-stage cancers. We demonstrate that human monocyte-derived DCs are endowed with significant cytotoxic activity against tumor cells following activation with LPS. The mechanism of DC-mediated tumor cell killing primarily involves peroxynitrites. This observed cytotoxic activity is restricted to immature DCs. Additionally, after killing, these cytotoxic DCs are able to activate tumor Ag-specific T cells. These observations may open important new perspectives for the use of autologous cytotoxic DCs in cancer immunotherapy strategies.     

Accelerated antigen sampling and transport by airway mucosal dendritic cells following inhalation of a bacterial stimulus

An increase in the tempo of local dendritic cell (DC)-mediated immune surveillance is a recognized feature of the response to acute inflammation at airway mucosal surfaces, and transient up-regulation of the APC functions of these DC preceding their emigration to regional lymph nodes has recently been identified as an important trigger for T cell-mediated airway tissue damage in diseases such as asthma. In this study, using a rat model, we demonstrate that the kinetics of the airway mucosal DC (AMDC) response to challenge with heat-killed bacteria is considerably more rapid and as a consequence more effectively compartmentalized than that in recall responses to soluble Ag. Notably, Ag-bearing AMDC expressing full APC activity reach regional lymph nodes within 30 min of cessation of microbial exposure, and in contrast to recall responses to nonpathogenic Ags, there is no evidence of local expression of APC activity within the airway mucosa preceding DC emigration. We additionally demonstrate that, analogous to that reported in the gut, a subset of airway intraepithelial DC extend their processes into the airway lumen. This function is constitutively expressed within the AMDC population, providing a mechanism for continuous immune surveillance of the airway luminal surface in the absence of "danger" signals.     

Novel and detrimental effects of lipopolysaccharide on in vitro generation of immature dendritic cells: involvement of mitogen-activated protein kinase p38

Dendritic cells (DCs) are recognized as major players in the regulation of immune responses to a variety of Ags, including bacterial agents. LPS, a Gram-negative bacterial cell wall component, has been shown to fully activate DCs both in vitro and in vivo. LPS-induced DC maturation involves activation of p38, extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinases, and NF-kappaB. Blocking p38 inhibits LPS-induced maturation of DCs. In this study we investigated the role of LPS in the in vitro generation of immature DCs. We report here that in contrast to the observed beneficial effects on DCs, the presence of LPS in monocyte culture retarded the generation of immature DCs. LPS not only impaired the morphology and reduced the yields of the cultured cells, but also inhibited the up-regulation of surface expression of CD1a, costimulatory and adhesion molecules. Furthermore, LPS up-regulated the secretion of IL-1beta, IL-6, IL-8, IL-10, and TNF-alpha; reduced Ag presentation capacity; and inhibited phosphorylation of ERK, but activated p38, leading to a reduced NF-kappaB activity in treated cells. Neutralizing Ab against IL-10, but not other cytokines, partially blocked the effects of LPS. Inhibiting p38 (by inhibitor SB203580) restored the morphology, phenotype, and Ag presentation capacity of LPS-treated cells. SB203580 also inhibited LPS-induced production of IL-1beta, IL-10, and TNF-alpha; enhanced IL-12 production; and recovered the activity of ERK and NF-kappaB. Thus, our study reveals that LPS has dual effects on DCs that are biologically important: activating existing DCs to initiate an immune response, and inhibiting the generation of new DCs to limit such a response.     

Airway activation of formyl peptide receptors inhibits Th1 and Th17 cell responses via inhibition of mediator release from immune and inflammatory cells and maturation of dendritic cells

Formyl peptide receptors (FPRs) are chemoattractant receptors that mediate inflammatory cell responses to infection. Recent evidence indicates that noneosinophilic asthma phenotypes can be developed by both Th1 and Th17 cell responses when exposed to LPS-containing allergens. In this study, we evaluated the effects of airway activation of FPRs by their synthetic agonist, Trp-Lys-Tyr-Met-Val-D-Met (W-peptide), on the development of Th1 and Th17 cell responses in a noneosinophilic asthma mouse model. A noneosinophilic asthma mouse model was generated by intranasal sensitization with 10 μg of LPS plus 75 μg of OVA on days 0, 1, 2, and 7. Mice were then challenged with 50 μg of OVA alone on days 14, 15, 21, and 22. W-peptide was administered during the sensitization period, and immune and inflammatory responses were evaluated after OVA challenge. Lung inflammation after OVA challenge was partly abolished by airway activation of FPRs during sensitization. Maturation of dendritic cells (DCs) and migration of DCs from the lung to lung-draining lymph nodes were inhibited by FPR activation. In addition, airway activation of FPRs inhibited allergen-specific T cell proliferation in the lymph nodes. Production of IL-12 and IL-6 (Th1- and Th17-polarizing cytokines) from lung DCs was decreased by airway activation of FPRs. This effect resulted in the inhibition of allergen-specific Th1 and Th17 cell responses. Airway activation of FPRs during sensitization effectively prevents the development of Th1 and Th17 cell responses induced by LPS-containing allergens via multiple mechanisms, such as inhibition of DC maturation and migration and the production of Th1- and Th7-polarizing cytokines.     

In vivo behavior of peptide-specific T cells during mucosal tolerance induction: antigen introduced through the mucosa of the conjunctiva elicits prolonged antigen-specific T cell priming followed by anergy

The mucosa of the conjunctiva is an important site of entry for environmental Ags as well as Ags emanating from the eye itself. However, very little is known about T cell recognition of Ag introduced through this important mucosal site. We have characterized the in vivo process of CD4 T cell recognition of Ag delivered via the conjunctival mucosa. Application of soluble OVA to the conjunctiva of BALB/c mice induced potent T cell tolerance. APC-presenting OVA peptide in vivo was only found in the submandibular lymph node and not in other lymph nodes, spleen, or nasal-associated lymphoid tissue. Similarly, in TCR transgenic DO11. 10 adoptive transfer mice, OVA-specific CD4+ T cell clonal expansion was only observed in the submandibular lymph node following conjunctival application of peptide. These experiments thus define a highly specific lymphatic drainage pathway from the conjunctiva. OVA-specific T cell clonal expansion peaked at day 3 following initiation of daily OVA administration and gradually declined during the 10-day treatment period, but remained elevated compared with nontreated adoptive transfer mice. During this period, the T cells expressed activation markers, and proliferated and secreted IL-2 in vitro in response to OVA stimulation. In contrast, these cells were unable to clonally expand in vivo, or proliferate in vitro following a subsequent OVA/CFA immunization. These results suggest that Ag applied to a mucosal site can be efficiently presented in a local draining lymph node, resulting in initial T cell priming and clonal expansion, followed by T cell anergy.     

Dendritic cell‐targeting DNA‐based nasal adjuvants for protective mucosal immunity to Streptococcus pneumoniae

To develop safe vaccines for inducing mucosal immunity to major pulmonary bacterial infections, appropriate vaccine antigens (Ags), delivery systems and nontoxic molecular adjuvants must be considered. Such vaccine constructs can induce Ag‐specific immune responses that protect against mucosal infections. In particular, it has been shown that simply mixing the adjuvant with the bacterial Ag is a relatively easy means of constructing adjuvant‐based mucosal vaccine preparations; the resulting vaccines can elicit protective immunity. DNA‐based nasal adjuvants targeting mucosal DCs have been studied in order to induce Ag‐specific mucosal and systemic immune responses that provide essential protection against microbial pathogens that invade mucosal surfaces. In this review, initially a plasmid encoding the cDNA of Flt3 ligand (pFL), a molecule that is a growth factor for DCs, as an effective adjuvant for mucosal immunity to pneumococcal infections, is introduced. Next, the potential of adding unmethylated CpG oligodeoxynucleotide and pFL together with a pneumococcal Ag to induce protection from pneumococcal infections is discussed. Pneumococcal surface protein A has been used as vaccine for restoring mucosal immunity in older persons. Further, our nasal pFL adjuvant system with phosphorylcholine‐keyhole limpet hemocyanin (PC‐KLH) has also been used in pneumococcal vaccine development to induce complete protection from nasal carriage by Streptococcus pneumoniae . Finally, the possibility that anti‐PC antibodies induced by nasal delivery of pFL plus PC‐KLH may play a protective role in prevention of atherogenesis and thus block subsequent development of cardiovascular disease is discussed.

     

Human tumor antigen MUC1 is chemotactic for immature dendritic cells and elicits maturation but does not promote Th1 type immunity

The immunostimulatory outcome of the interactions of many pathogens with dendritic cells (DCs) has been well characterized. There are many fewer examples of similar interactions between DCs and self-molecules, especially the abnormal self-proteins such as many tumor Ags, and their effects on DC function and the immune response. We show that human epithelial cell Ag MUC1 mucin is recognized in its aberrantly glycosylated form on tumor cells by immature human myeloid DCs as both a chemoattractant (through its polypeptide core) and a maturation and activation signal (through its carbohydrate moieties). On encounter with MUC1, similar to the encounter with LPS, immature DCs increase cell surface expression of CD80, CD86, CD40, and CD83 molecules and the production of IL-6 and TNF-alpha cytokines but fail to make IL-12. When these DCs are cocultured with allogeneic CD4+ T cells, they induce production of IL-13 and IL-5 and lower levels of IL-2, thus failing to induce a type 1 response. Our data suggest that, in vivo in cancer patients, MUC1 attracts immature DCs to the tumor through chemotaxis and subverts their function by negatively affecting their ability to stimulate type 1 helper T cell responses important for tumor rejection.     

Antigen-antibody immune complexes empower dendritic cells to efficiently prime specific CD8+ CTL responses in vivo

Dendritic cells (DCs) require a maturation signal to acquire efficient CTL-priming capacity. In vitro FcgammaR-mediated internalization of Ag-Ab immune complexes (ICs) can induce maturation of DCs. In this study, we show that IC-induced DC maturation in vitro enables DCs to prime peptide-specific CD8+ CTLs in vivo, independently of CD4+ Th cells. Importantly, OVA/anti-OVA IC-treated DCs not only primed CD8+ CTLs to an exogenously loaded peptide nonrelated to OVA, but also efficiently primed CTLs against the dominant CTL epitope derived from the OVA Ag present in the ICs. Our studies show that ICs fulfill a dual role in priming of CD8+ CTL responses to exogenous Ags: enhancement of Ag uptake by DCs and activation of DCs, resulting in "license to kill." These findings indicate that the presence of specific Abs can crucially affect the induction of cytotoxic cellular responses.