Role of B7 costimulatory molecules in the adjuvant activity of the heat-labile enterotoxin of Escherichia coli

Monophosphoryl lipid A enhances nontypeable Haemophilus influenzae-specific mucosal and systemic immune responses by intranasal immunization

OBJECTIVE

Acute otitis media (AOM) is one of the most common infectious diseases in children. Nontypeable Haemophilus influenzae (NTHi) is Gram-negative bacteria that are considered major pathogens of AOM and respiratory tract infections. In this study, we used monophosphoryl lipid A (MPL), a toll-like receptor (TLR) 4 agonist, as an adjuvant to induce mucosal immune responses against NTHi to enhance bacterial clearance from the nasopharynx.

METHODS

Mice were administered 10 μg outer membrane protein (OMP) from NTHi and 0, 10, or 20 μg MPL intranasally once a week for 3 weeks. Control mice were administered phosphate-buffered saline alone. After immunization, these mice were challenged with NTHi. At 6 and 12 h after bacterial challenge, the mice were killed and nasal washes and sera were collected. The numbers of NTHi- and OMP-specific antibodies were quantified by enzyme-linked immunosorbent assay.

RESULTS

The MPL 10 and 20 μg group produced a significant reduction in the number of bacteria recovered from the nasopharynx at 12 h after bacterial challenge compared to the control group. OMP-specific IgA titers were also augmented in the MPL groups compared to the control and OMP groups.

CONCLUSION

MPL is suitable for eliciting effective mucosal immune responses against NTHi in the nasopharynx. These results demonstrate the possibility of an adjuvant that involves stimulation of the innate immune system by TLR4 agonists such as MPL for mucosal vaccination.

The role of glycogen synthase kinase 3 in regulating IFN-β-mediated IL-10 production

The ability of IFN-β to induce IL-10 production from innate immune cells is important for its anti-inflammatory properties and is believed to contribute to its therapeutic value in treating multiple sclerosis patients. In this study, we identified that IFN-β stimulates IL-10 production by activating the JAK1- and PI3K-signaling pathways. JAK1 activity was required for IFN-β to activate PI3K and Akt1 that resulted in repression of glycogen synthase kinase 3 (GSK3)-β activity. IFN-β-mediated suppression of GSK3-β promoted IL-10, because IL-10 production by IFN-β-stimulated dendritic cells (DC) expressing an active GSK3-β knockin was severely reduced, whereas pharmacological or genetic inhibition of GSK3-β augmented IL-10 production. IFN-β increased the phosphorylated levels of CREB and STAT3 but only CREB levels were affected by PI3K. Also, a knockdown in CREB, but not STAT3, affected the capacity of IFN-β to induce IL-10 from DC. IL-10 production by IFN-β-stimulated DC was shown to suppress IFN-γ and IL-17 production by myelin oligodendrocyte glycoprotein-specific CD4(+) T cells, and this IL-10-dependent anti-inflammatory effect was enhanced by directly targeting GSK3 in DC. These findings highlight how IFN-β induces IL-10 production and the importance that IL-10 plays in its anti-inflammatory properties, as well as identify a therapeutic target that could be used to increase the IL-10-dependent anti-inflammatory properties of IFN-β.

Mucosal adjuvants and long-term memory development with special focus on CTA1-DD and other ADP-ribosylating toxins

The ultimate goal for vaccination is to stimulate protective immunological memory. Protection against infectious diseases not only relies on the magnitude of the humoral immune response, but more importantly on the quality and longevity of it. Adjuvants are critical components of most non-living vaccines. Although little attention has been given to qualitative aspects of the choice of vaccine adjuvant, emerging data demonstrate that this function may be central to vaccine efficacy. In this review we describe efforts to understand more about how adjuvants influence qualitative aspects of memory development. We describe recent advances in understanding how vaccines induce long-lived plasma and memory B cells, and focus our presentation on the germinal center reaction. As mucosal vaccination requires powerful adjuvants, we have devoted much attention to the adenosine diphosphate (ADP)-ribosylating cholera toxin and the CTA1-DD adjuvants as examples of how mucosal adjuvants can influence induction of long-term memory.

Role of Toll-like receptors in host responses to a virulence antigen of Streptococcus mutans expressed by a recombinant, attenuated Salmonella vector vaccine

In the present study, we investigated the role of Toll-like receptors (TLRs) in host responses to the saliva-binding region (SBR) of Streptococcus mutans expressed by a recombinant, attenuated Salmonella vaccine. C57BL/6 wild type (wt), TLR2-/-, TLR4-/- and MyD88-/- mice were immunized by the intranasal route on days 0, 18 and boosted on day 98 with Salmonella typhimurium BRD 509 containing a plasmid encoding SBR. Serum and saliva samples were collected throughout the experiment and assessed for antibody activity by ELISA. Evidence is provided that the induction of a serum IgG2a (Th1-type) anti-SBR antibody response involved TLR2 signaling, whereas the anti-Salmonella response involved signaling through TLR4. The adaptor molecule MyD88 was not essential for the induction of a primary Th1-type response to SBR or Salmonella, but was necessary for a secondary response to SBR. Furthermore, the absence of TLR2, TLR4 or MyD88 resulted in enhanced Th2-type serum IgG1 anti-SBR and anti-Salmonella responses. Mucosal IgA responses to SBR were TLR2-, TLR4- and MyD88-dependent, while IgA responses to Salmonella were TLR4- and MyD88-dependent.

Probing local innate immune responses after mucosal immunisation

Background

Intranasal immunisation is potentially a very effective route for inducing both mucosal and systemic immunity to an infectious agent.

Methods

Balb/c mice were intranasally immunised with the mucosal adjuvant heat labile toxin and the Mycobacterium tuberculosis fusion protein Ag85B-ESAT6 and early changes in innate immune responses within local mucosal tissues were examined using flow cytometry and confocal microscopy. Antigen-specific humoral and cellular immune responses were also evaluated.

Results

Intranasal immunisation induced significant changes in both number and distribution of dendritic cells, macrophages and neutrophils within the nasal-associated lymphoid tissue and cervical lymph nodes in comparison to controls as early as 5 h post immunisation. Immunisation also resulted in a rapid and transient increase in activation marker expression first in the nasal-associated lymphoid tissue, and then in the cervical lymph nodes. This heightened activation status was also apparent from the pro-inflammatory cytokine profiles of these innate populations. In addition we also showed increased expression and distribution of a number of different cell adhesion molecules early after intranasal immunisation within these lymphoid tissues. These observed early changes correlated with the induction of a T_H1 type immune response.

Conclusions

These data provide insights into the complex nature of innate immune responses induced following intranasal immunisation within the upper respiratory tract, and may help clarify the concepts and provide the tools that are needed to exploit the full potential of mucosal vaccines.

Bacterial toxins as immunomodulators

Bacterial toxins are the causative agent at pathology in a variety of diseases. Although not always the primary target of these toxins, many have been shown to have potent immunomodulatory effects, for example, inducing immune responses to co-administered antigens and suppressing activation of immune cells. These abilities of bacterial toxins can be harnessed and used in a therapeutic manner, such as in vaccination or the treatment of autoimmune diseases. Furthermore, the ability of toxins to gain entry to cells can be used in novel bacterial toxin based immuno-therapies in order to deliver antigens into MHC Class I processing pathways. Whether the immunomodulatory properties of these toxins arose in order to enhance bacterial survival within hosts, to aid spread within the population or is pure serendipity, it is interesting to think that these same toxins potentially hold the key to preventing or treating human disease.

Effect of adjuvants and route of immunizations on the immune response to recombinant plague antigens

In this study, we compare four different adjuvants, LT(R192G), CpG ODN, MPL((R))TDM, and alum, for their ability to affect the magnitude, distribution, and duration of antibody responses against F1-V, the lead-candidate antigen for the next generation vaccine against plague, in a murine model. In addition, three different routes of immunization-intranasal (IN), transcutaneous (TC), and subcutaneous (SC) were compared with each adjuvant. Since aerosol exposure to biological warfare agents is of primary concern, both serum and bronchioalveolar lavage (BAL) were analyzed for antigen-specific antibody responses. The most significant findings of the study reported here are that (1) the adjuvant influences the Type 1/Type 2 balance of the antibody response in both the serum and BAL, (2) mucosal immunization is not necessary to obtain F1-V-specific BAL responses, (3) non-traditional adjuvants such as LT(R192G) work when delivered subcutaneously, (4) the route of immunization affects the magnitude of the immune response, and (5) F1-V is highly immunogenic by some routes even in the absence of an exogenously applied adjuvant. These studies provide important insights into the influence of different classes of adjuvants on the immune outcome in biodefense vaccines and for development of new-generation vaccines against other pathogens as well.

Role of CD80 and CD86 in host immune responses to the recombinant hemagglutinin domain of Porphyromonas gingivalis gingipain and in the adjuvanticity of cholera toxin B and monophosphoryl lipid A

The gingipains of Porphyromonas gingivalis have been implicated in the virulence of this bacterium, and antibodies to the hemagglutinin/adhesin domain (HArep) of the gingipains have been shown to protect against P. gingivalis colonization. However, the cellular mechanisms involved in host responses to HArep have not been elucidated. The purpose of the present study was to determine the functional role of CD80 and CD86 in mediating systemic and mucosal immune responses to the recombinant HArep derived from the gingipain Kgp (Kgp-HArep) after intranasal (i.n.) immunization. We also investigated the effect of the mucosal adjuvants the B subunit of cholera toxin (CTB) and monophosphoryl lipid A (MPL) on the functional role of the costimulatory molecules for the induction of systemic and mucosal responses to Kgp-HArep. The in vivo functional roles of CD80 and CD86 were assessed in C57BL/6 wild-type (wt), CD80(-/-), CD86(-/-) and CD80/CD86(-/-) mice following intranasal immunization with Kgp-HArep with or without adjuvant. Serum IgG and mucosal IgA antibody responses were induced following i.n. immunization of mice with Kgp-HArep, and were potentiated by CTB or MPL. A differential requirement of CD80and/or CD86 was observed for systemic IgG anti-Kgp-HArep responses following the primary and secondary immunization with antigen alone or antigen+adjuvant. Compared to wt and CD80(-/-) mice, CD86(-/-) mice had reduced serum IgG anti-Kgp-HArep responses following the second immunization with antigen alone or antigen+CTB, whereas similar levels of serum IgG anti-Kgp-HArep antibody activity were observed in wt, CD80(-/-) and CD86(-/-) mice immunized with antigen+MPL. Analysis of the serum IgG subclass responses revealed that CD80 influenced both Th1- and Th2-like IgG subclass responses, while CD86 preferentially influenced a Th2-associated IgG subclass response to Kgp-HArep. Mucosal IgA anti-Kgp-HArep responses in saliva and vaginal washes were diminished in CD86(-/-) mice. In vitro stimulation of murine bone marrow-derived dendritic cells with Kgp-HArep, CTB and MPL resulted in an up-regulation of CD80 and especially CD86 expression. Taken together, our results demonstrate that CD80 and CD86 can play distinct as well as redundant roles in mediating a systemic immune response and that CD86 plays a unique role in mediating a mucosal response to Kgp-HArep following immunization via the i.n. route alone or with adjuvant.

Enhancing DNA vaccine potency by modifying the properties of antigen-presenting cells

DNA vaccines represent a potentially promising approach for antigen-specific immunotherapy. Advances in our knowledge of the adaptive immune system have indicated that professional antigen-presenting cells, especially dendritic cells (DCs), play a key role in the generation of antigen-specific immune responses. Thus, the modification of the properties of DCs represents an important strategy for enhancing the potency of DNA vaccines. This review discusses strategies to increase the number of antigen-expressing DCs, enhance antigen expression, processing and presentation in DCs, promote the activation and function of DCs, and improve DC and T-cell interaction, in order to optimize DNA vaccine-elicited immune responses. Continuing progress in our understanding of DC and T-cell biology serves as a foundation for further improvement of DNA vaccine potency, which may lead to future clinical applications of DNA vaccines for the control of infectious diseases and malignancies.

Regulation of intestinal immunity: effects of the oral adjuvant Escherichia coli heat-labile enterotoxin on migrating dendritic cells

Escherichia coli heat-labile enterotoxin (Etx) is an oral adjuvant in mice. We show that this is also true for rats. To understand this adjuvant activity we examined lymph dendritic cells (DC) migrating from the intestine to mesenteric lymph nodes (MLN) in animals fed Etx. These DC can prime antigen-specific antibody responses. We show that in rats the small intestine contains 7-24 million DC and 8 x 10(5 )of these migrate to MLN each day. Surprisingly, Etx does not stimulate increased migration of lymph DC. However, oral Etx affects the activation, antigen transport and localization of migratory DC. Specifically, expression of CD25 increases on the CD172a(high) subset of lymph DC. Oral Etx also increases the number of CD172a(high) lymph DC containing co-administered ovalbumin. CD172a(high) lymph DC treated with Etx in vitro, or purified from the lymph of animals fed Etx, stimulate stronger proliferative responses from primed T cells. Etx also directs more of the CD172a(high) lymph DC into the central region of the MLN T cell areas. This change in DC localization is associated with an increase in the expression of CCR7. These data help advance our understanding of the role of DC in initiating mucosal immune responses in vivo.

Comparison of immune responses in parenteral FaeG DNA primed pigs boosted orally with F4 protein or reimmunized with the DNA vaccine

We previously showed that an intradermal (i.d.) FaeG DNA prime (2x)-oral F4 protein boost immunization induces a systemic response and weakly primes a mucosal IgG response in pigs, especially when plasmid vectors encoding the A and B subunit of the E. coli thermo-labile enterotoxin (LT) are added to the DNA vaccine. In the present study, we evaluated whether addition of 1alpha,25-dihydroxyvitamin D(3) (vitD(3)) to the DNA vaccine could further enhance this mucosal priming and/or modulate the antibody response towards IgA. To further clarify priming of systemic and mucosal responses by the i.d. DNA vaccination, we firstly compared the localization of the F4-specific antibody response in pigs that were orally boosted with F4 to that in pigs that received a third i.d. DNA immunization and secondly evaluated cytokine mRNA expression profiles after i.d. DNA vaccination. The i.d. DNA prime (2x)-oral F4 boost immunization as well as the 3 i.d. DNA vaccinations induced mainly a systemic response, with a higher response observed following the heterologous protocol. Co-administration of vitD(3), and especially of the LT vectors, enhanced this response. Furthermore, only the heterologous immunization resulted in a weak mucosal priming, which appeared to require the presence of the LT vectors or vitD(3) as adjuvants. In addition, the LT vectors strongly enhanced the FaeG-specific lymphocyte proliferation and this was accompanied by the absence of a clear IL-10 response. However, despite two DNA immunizations in the presence of these adjuvants and an oral F4 boost, we failed to demonstrate the secretory IgA response needed to be protective against enterotoxigenic E. coli.

Mutants of type II heat-labile enterotoxin LT-IIa with altered ganglioside-binding activities and diminished toxicity are potent mucosal adjuvants

The structure and function LT-IIa, a type II heat-labile enterotoxin of Escherichia coli, are closely related to the structures and functions of cholera toxin and LT-I, the type I heat-labile enterotoxins of Vibrio cholerae and enterotoxigenic Escherichia coli, respectively. While LT-IIa is a potent systemic and mucosal adjuvant, recent studies demonstrated that mutant LT-IIa(T34I), which exhibits no detectable binding activity as determined by an enzyme-linked immunosorbent assay, with gangliosides GD1b, GD1a, and GM1 is a very poor adjuvant. To evaluate whether other mutant LT-IIa enterotoxins that also exhibit diminished ganglioside-binding activities have greater adjuvant activities, BALB/c mice were immunized by the intranasal route with the surface adhesin protein AgI/II of Streptococcus mutans alone or in combination with LT-IIa, LT-IIa(T14S), LT-IIa(T14I), or LT-IIa(T14D). All three mutant enterotoxins potentiated strong mucosal immune responses that were equivalent to the response promulgated by wt LT-IIa. All three mutant enterotoxins augmented the systemic immune responses that correlated with their ganglioside-binding activities. Only LT-IIa and LT-IIa(T14S), however, enhanced expression of major histocompatibility complex class II and the costimulatory molecules CD40, CD80, and CD86 on splenic dendritic cells. LT-IIa(T14I) and LT-IIa(T14D) had extremely diminished toxicities in a mouse Y1 adrenal cell bioassay and reduced abilities to induce the accumulation of intracellular cyclic AMP in a macrophage cell line.

Adjuvants modulating mucosal immune responses or directing systemic responses towards the mucosa

In developing veterinary mucosal vaccines and vaccination strategies, mucosal adjuvants are one of the key players for inducing protective immune responses. Most of the mucosal adjuvants seem to exert their effect via binding to a receptor/or target cells and these properties were used to classify the mucosal adjuvants reviewed in the present paper: (1) ganglioside receptor-binding toxins (cholera toxin, LT enterotoxin, their B subunits and mutants); (2) surface immunoglobulin binding complex CTA1-DD; (3) TLR4 binding lipopolysaccharide; (4) TLR2-binding muramyl dipeptide; (5) Mannose receptor-binding mannan; (6) Dectin-1-binding ss 1,3/1,6 glucans; (7) TLR9-binding CpG-oligodeoxynucleotides; (8) Cytokines and chemokines; (9) Antigen-presenting cell targeting ISCOMATRIX and ISCOM. In addition, attention is given to two adjuvants able to prime the mucosal immune system following a systemic immunization, namely 1alpha, 25(OH)2D3 and cholera toxin.

Cellular mechanisms of the adjuvant activity of the flagellin component FljB of Salmonella enterica Serovar Typhimurium to potentiate mucosal and systemic responses

An expanding area of interest is the utilization of microbe-based components to augment mucosal and systemic immune responses to target antigens. Thus, the aim of the present study was to assess if the flagellin component FljB from Salmonella enterica serovar Typhimurium could act as a mucosal adjuvant and then to determine the cellular mechanism(s) by which FljB mediates its adjuvant properties. To determine if FljB could act as a mucosal adjuvant, mice were immunized by the intranasal (i.n.) route with antigen alone or in conjunction with FljB. Additionally, we assessed how FljB affected the levels of the costimulatory molecules B7-1 and B7-2 on dendritic cells by flow cytometry and determined the functional role these costimulatory molecules played in the adjuvant properties of FljB in vivo. Mice immunized by the i.n. route with antigen and FljB exhibited significantly elevated levels of mucosal and systemic antibody and CD4(+)-T-cell responses compared to mice given antigen only. Stimulation of dendritic cells in vitro with FljB resulted in a pronounced increase in the surface expression of B7-1 and B7-2. The percentage of dendritic cells expressing B7-2 but not B7-1 increased significantly when stimulated with FljB over a concentration range of 10 to 10,000 ng/ml. Immunization of wild-type and B7-1, B7-2, and B7-1/2 knockout mice by the i.n. route revealed that the ability of FljB to increase B7-2 expression is largely responsible for its adjuvant effect in vivo. These findings demonstrate that FljB can act as an effective mucosal adjuvant and that its ability to enhance the level of B7-2 expression is predominantly responsible for its adjuvant properties.

Effectiveness of the B subunit of cholera toxin in potentiating immune responses to the recombinant hemagglutinin/adhesin domain of the gingipain Kgp from Porphyromonas gingivalis

The hemagglutinin/adhesin HArep domain is present in the gingipains HRgpA and Kgp and in the hemagglutinin HagA of Porphyromonas gingivalis and is felt to be important in the virulence of this bacterium. In the present study, we determined the immunogenicity of recombinant HArep from the gingipain Kgp (termed Kgp-rHArep) and the effectiveness of the B subunit of cholera toxin (CTB), compared to other adjuvants in potentiating a specific response to Kgp-rHArep following intranasal (i.n.) immunization of mice. Furthermore, we determined the effectiveness of anti-Kgp-rHArep antibodies in protection against P. gingivalis invasion of epithelial cells. Evidence is provided that Kgp-rHArep was effective in inducing immune responses following systemic or mucosal immunization. Kgp-rHArep induced both a Th1- and Th2-type response following i.n. immunization. Immunization of mice with Kgp-rHArep and CTB, either admixed or chemically conjugated to the antigen, via the i.n. route, resulted in a significant augmentation of the systemic and mucosal immune response to Kgp-rHArep, which was similar to or higher than the responses seen in mice immunized with antigen and the other adjuvants tested. CTB and the heat-labile toxin of Escherichia coli potentiated a Th1- and Th2-type response to Kgp-rHArep, whereas the adjuvant monophosphoryl lipid A preferentially promoted a Th1-type response to the antigen. Furthermore, anti-Kgp-rHArep antibodies were shown to protect against P. gingivalis invasion of epithelial cells in an in vitro system. These results demonstrate the effectiveness of certain mucosal adjuvants in potentiating and in altering the nature of the immune response to Kgp-rHArep following i.n. immunization, and provide evidence for the potential usefulness of Kgp-rHArep for the development of a vaccine against periodontal disease.

A mutant of Escherichia coli enterotoxin inducing a specific Thl-type of T cells to varicella-zoster vaccine enhances the production of IL-12 by IFNgamma-stimulated macrophages

A mutant of Escherichia coli enterotoxin induces specific Thl-type T cells to varicella-zoster vaccine. The mutant increased IL-12p40, TNFalpha and nitric oxide production by IFNgamma-stimulated bone marrow macrophages but cholera toxin did not. Anti-TNFalpha antibodies blocked its stimulation of IL-12p40 production but iNOS inhibitor did not. IL-12p40 and IL-12p35 production was stimulated at the level of mRNA formation by the mutant. Cholera toxin suppressed IL-12beta1 expression by spleen T cells stimulated with anti-CD3 antibodies but the mutant did not. These findings indicate that the mutant may induce Thl-type response to the vaccine through its IL-12 and TNFalpha induction by macrophages.

Mucosal adjuvants

Induction of immune responses following oral immunization is frequently dependent upon the co-administration of appropriate adjuvants that can initiate and support the transition from innate to adaptive immunity. The three bacterial products with the greatest potential to function as mucosal adjuvants are the ADP-ribosylating enterotoxins (cholera toxin and the heat-labile enterotoxin of Escherichia coli), synthetic oligodeoxynucleotides containing unmethylated CpG dinucleotides (CpG ODN), and monophosphoryl lipid A (MPL). The mechanism of adjuvanticity of the ADP-ribosylating enterotoxins is the subject of considerable debate. Our own view is that adjuvanticity is an outcome and not an event. It is likely that these molecules exert their adjuvant function by interacting with a variety of cell types, including epithelial cells, dendritic cells, macrophages, and possibly B- and T-lymphocytes. The adjuvant activities of CpG and MPL are due to several different effects they have on innate and adaptive immune responses and both MPL and CpG act through MyD88-dependent and -independent pathways. This presentation will summarize the probable mechanisms of action of these diverse mucosal adjuvants and discuss potential synergy between these molecules for use in conjunction with plant-derived vaccines.

Innate imprinting by the modified heat-labile toxin of Escherichia coli (LTK63) provides generic protection against lung infectious disease

In a healthy individual, the lung contains few lymphoid cells. However, amplified immune responses, as exemplified during lung infection, can cause extensive tissue damage. We have previously demonstrated that one lung infection modulates the immunopathological outcome to a subsequent unrelated pathogen. Mimicking heterologous immunity may provide a means of enhancing both innate and acquired immunity. We now show that prior lung administration of a modified heat-labile toxin from Escherichia coli (LTK63) enhances immunity to respiratory syncytial virus, influenza virus, and the fungus Cryptococcus neoformans. Treatment with LTK63 decreased lung inflammation and tissue damage and improved the ability to resolve the infection. APCs expressing the activation markers MHC class II, CD80, and CD40 increased in number in the lung. LTK63 treatment increased the pathogen-specific IgA response in the nasal mucosa and simultaneously decreased inflammatory cytokine production (IFN-gamma and TNF-alpha) after infection. The number of activated CD8(+)CD44(+) T cells and the respiratory syncytial virus- or influenza-specific CD8-proliferative responses increased, although the total inflammatory infiltrate was reduced. LTK63 treatment matured lung APCs (LTK63 prevented efficient presentation of whole OVA to DO11.10 cells, whereas OVA peptide presentation was unaffected), enhanced immunity in both a Th1 and Th2 environment, was long lasting, and was not pathogen or host strain specific; the protective effects were partially independent of T and B cells. Innate imprinting by toxin-based immunotherapeutics may provide generic protection against infectious disease in the lung, without the need for coadministered pathogen-specific Ag.

The Mycoplasma-derived macrophage-activating 2-kilodalton lipopeptide triggers global immune activation on nasal mucosa-associated lymphoid tissues

A better knowledge on how immune responses are initiated in mucosal tissues would facilitate the design of new mucosal vaccines, as well as improve our understanding on host defense against infection. We investigated the mechanisms of adjuvanticity of the Mycoplasma-derived macrophage-activating 2-kDa lipopeptide (MALP-2), which binds to the heterodimer formed by the Toll-like receptors 2 and 6 (TLR2 and -6), at the level of the murine nasal mucosa-associated lymphoid tissues (NALT). TLR2 expression analysis demonstrated that several cell types from the nasal cavity were able to overexpress this receptor, either constitutively (such as B cells) or after stimulation (i.e., T cells). MALP-2 stimulated a strong B-cell activation. In addition, the antigen presentation capacity of dendritic cells was improved after in vivo loading with antigen in the presence of MALP-2. We also observed an up-regulated expression of activation markers and adhesion molecules on T cells, suggesting that they have enhanced responsiveness and interaction potential. Quantitative reverse transcription-PCR analysis showed that MALP-2 administration resulted in the stimulation of a proinflammatory cascade. We observed an early up-regulated expression of IP-10, MCP-1, MCP-3, MIP-1alpha, MIP-2, and CCR-2 which was reversed within 36 h. The obtained results demonstrated that MALP-2 creates a reversible local microenvironment which promotes effective priming of T and B cells in the NALT.

Role of B7 costimulatory molecules in mediating systemic and mucosal antibody responses to attenuated Salmonella enterica serovar Typhimurium and its cloned antigen

The purpose of the present study was to evaluate the ability of an attenuated Salmonella enterica serovar Typhimurium vaccine strain to up-regulate B7-1 and B7-2 on antigen-presenting cells and to examine the functional roles these costimulatory molecules play in mediating immune responses to Salmonella and to an expressed cloned antigen, the saliva-binding region (SBR) of antigen I/II. In vitro stimulation of B cells (B220+), macrophages (CD11b+), and dendritic cells (CD11c+) with S. enterica serovar Typhimurium induced an up-regulation of B7-2 and, especially, B7-1 expression. The in vivo functional roles of B7-1, B7-2, and B7-1/2 were evaluated in BALB/c wild-type and B7-1, B7-2, and B7-1/2 knockout (KO) mice following intranasal immunization with the Salmonella expressing the cloned SBR. Differential requirements for B7-1 and B7-2 were observed upon primary and secondary immunizations. Compared to wild-type controls, B7-1 and B7-2 KO mice had reduced mucosal and systemic anti-Salmonella antibody responses after a single immunization, while only B7-1 KO mice exhibited suppressed anti-Salmonella antibody responses following the second immunization. Mucosal and systemic antibody responses to SBR were reduced following the primary immunization, whereas a compensatory role for either B7-1 or B7-2 was observed after the second immunization. B7-1/2 double KO mice failed to induce detectable levels of mucosal or systemic immunoglobulin A (IgA) or IgG antibody responses to either Salmonella or SBR. These findings demonstrate that B7-1 and B7-2 can play distinct as well as redundant roles for mediating mucosal and systemic antibody responses, which are likely dependent upon the nature of the antigen.