Salmonella induces a switched antibody response without germinal centers that impedes the extracellular spread of infection

T-dependent Ab responses are characterized by parallel extrafollicular plasmablast growth and germinal center (GC) formation. This study identifies that, in mice, the Ab response against Salmonella is novel in its kinetics and its regulation. It demonstrates that viable, attenuated Salmonella induce a massive early T-dependent extrafollicular response, whereas GC formation is delayed until 1 mo after infection. The extrafollicular Ab response with switching to IgG2c, the IgG2a equivalent in C57BL/6 mice, is well established by day 3 and persists through 5 wk. Switching is strongly T dependent, and the outer membrane proteins are shown to be major targets of the early switched IgG2c response, whereas flagellin and LPS are not. GC responses are associated with affinity maturation of IgG2c, and their induction is associated with bacterial burden because GC could be induced earlier by treating with antibiotics. Clearance of these bacteria is not a consequence of high-affinity Ab production, for clearance occurs equally in CD154-deficient mice, which do not develop GC, and wild-type mice. Nevertheless, transferred low- and high-affinity IgG2c and less efficiently IgM were shown to impede Salmonella colonization of splenic macrophages. Furthermore, Ab induced during the infection markedly reduces bacteremia. Thus, although Ab does not prevent the progress of established splenic infection, it can prevent primary infection and impedes secondary hemogenous spread of the disease. These results may explain why attenuated Salmonella-induced B cell responses are protective in secondary, but not primary infections.     

Mannose-binding lectin variant associated with severe malaria in young African children

Mannose-binding lectin (MBL) is a serum protein which initiates innate immune responses to microbial pathogens by binding to non-self surface oligosaccharides. MBL deficiency is the most common congenital immunodeficiency of human and has been shown to predispose to infections, particularly in children and immune compromised. In a matched case-control study among 870 Ghanaian children, we examined the influence of six polymorphisms of the MBL2 gene on Plasmodium falciparum infection and severe malaria. A missense mutation resulting in low MBL activity (MBL2*C) was found in 35% of healthy controls, but in 42% of asymptomatically infected children (P=0.01), and in 46% of patients with severe malaria (P=0.007). Heterozygosity for MBL2*C was associated with increased odds of infection (odds ratio (OR), 1.6; 95% confidence interval (CI), 1.1-2.1), severe malaria (OR, 1.7; 95% CI, 1.2-2.4), and of severe anemia in particular (OR, 2.3; 95% CI, 1.4-3.8). The population attributable fraction of severe malaria cases attributable to MBL2*C heterozygosity was 17%. Our results suggest that the MBL pathway of the complement system is a critical determinant of both, susceptibility to P. falciparum infection and manifestation of severe malaria, particularly in young children in whom specific immune responses are weak or absent.     

Antibody production in mice deficient for complement receptors 1 and 2 can be induced by IgG/Ag and IgE/Ag, but not IgM/Ag complexes

Deficiencies in C factors C2, C3, or C4 as well as lack of C receptors 1 and 2 (CR1/2) lead to impaired Ab production. Classical pathway activation plays a major role, as mice deficient in factor B, a key factor in the alternative pathway, have normal Ab production. Abs in complex with their specific Ag are known to feedback regulate the Ab response, and enhanced responses are initiated by IgM, IgE, and IgG. IgM acts via the C system, whereas IgE and IgG can operate independently of C via Fc receptors. Here we have investigated whether these isotypes are able to enhance Ab responses in mice lacking CR1/2. SRBC-specific IgM, administered with SRBC, does not enhance Ab responses in these animals. In contrast, 2,4, 6-trinitrophenyl-specific IgE and IgG2a, administered with BSA-2,4, 6-trinitrophenyl, induce potent Ab responses in CR1/2-deficient mice. Additionally, BSA administered with CFA or alum induced strong Ab responses in the absence of CR1/2. These results indicate that CR1/2 is needed to promote IgM-mediated induction of primary Ab responses. The data also show that the need for CR1/2 can be circumvented by Abs typical of a secondary immune response forming complexes with Ag or by conventional adjuvants, presumably mimicking physiological inflammatory reactions.     

Loss of discrete memory B cell subsets is associated with impaired immunization responses in HIV-1 infection and may be a risk factor for invasive pneumococcal disease

Invasive pneumococcal infection is an important cause of morbidity and mortality in HIV-1-infected individuals. B cells play an important role in maintaining serologic memory after infection. IgM memory B cells are significantly reduced in HIV-1-infected patients and their frequency is similar to that observed in other patient groups (splenectomized individuals and patients with primary Ab deficiency) who are also known to have an increased risk of invasive pneumococcal infection. Antiretroviral therapy does not restore marginal zone B cell percentages. Immunization with the 23-valent polysaccharide pneumococcal vaccine shows that HIV-1-infected patients have impaired total IgM and IgG pneumococcal vaccines compared with healthy controls. Loss of switched memory B cells was associated with impaired tetanus toxoid IgG vaccine responses. Results of this study demonstrate that defects in B cell memory subsets are associated with impaired humoral immune responses in HIV-1 patients who are receiving antiretroviral therapy and may be a contributory factor to the increased risk of invasive pneumococcal infection observed in HIV-1 infection.     

Low mannose-binding lectin function is associated with sepsis in adult patients

Mannose-binding lectin (MBL) is an innate immune system pattern recognition molecule that kills a wide range of pathogens via the lectin complement pathway. MBL deficiency is associated with severe infection but the best measure of this deficiency is undecided. We investigated the influence of MBL functional deficiency on the development of sepsis in 195 adult patients, 166 of whom had bloodstream infection and 35 had pneumonia. Results were compared with 236 blood donor controls. MBL function (C4b deposition) and levels were measured by enzyme-linked immunosorbent assay. Using receiver-operator characteristics of MBL function in healthy controls, we identified a level of <0.2 U microL(-1) as a highly discriminative marker of low MBL2 genotypes. Median MBL function was lower in sepsis patients (0.18 U microL(-1)) than in controls (0.48 U microL(-1), P<0.001). MBL functional deficiency was more common in sepsis patients than controls (P<0.001). MBL functional deficient patients had significantly higher sequential organ failure assessment (SOFA) scores and higher MBL function and levels were found in patients with SOFA scores predictive of good outcome. Deficiency of MBL function appears to be associated with bloodstream infection and the development of septic shock. High MBL levels may be protective against severe sepsis.     

Central role of complement in passive protection by human IgG1 and IgG2 anti-pneumococcal antibodies in mice

Streptococcus pneumoniae is an important cause of morbitity and mortality worldwide. Capsule-specific IgG1 and IgG2 Abs are induced upon vaccination with polysaccharide-based vaccines that mediate host protection. We compared the protective capacity of human recombinant serogroup 6-specific IgG1 and IgG2 Abs in mice deficient for either leukocyte FcR or complement factors. Human IgG1 was found to interact with mouse leukocyte FcR in vitro, whereas human IgG2 did not. Both subclasses induced complement activation, resulting in C3c deposition on pneumococcal surfaces. Passive immunization of C57BL/6 mice with either subclass before intranasal challenge with serotype 6A induced similar degrees of protection. FcgammaRI- and III-deficient mice, as well as the combined FcgammaRI, II, and III knockout mice, were protected by passive immunization, indicating FcR not to be essential for protection. C1q or C2/factor B knockout mice, however, were not protected by passive immunization. Passively immunized C2/factor B(-/-) mice displayed higher bacteremic load than C1q(-/-) mice, supporting an important protective role of the alternative complement pathway. Spleens from wild-type and C1q(-/-) mice showed hyperemia and thrombotic vessel occlusion, as a result of septicemic shock. Notably, thrombus formation was absent in spleens of C2/factor B(-/-) mice, suggesting that the alternative complement pathway contributes to shock-induced intravascular coagulation. These studies demonstrate complement to play a central role in Ab-mediated protection against pneumococcal infection in vivo, as well as in bacteremia-associated thrombotic complications.     

More is not necessarily better: prozone-like effects in passive immunization with IgG

Despite a century of study, the relationship between Ag-specific Ig concentration and protection remains poorly understood for the majority of pathogens. In certain conditions, administration of high Ab doses before challenge with an infectious agent can be less effective than smaller Ab doses, a phenomenon which is consistent with a prozone-like effect. In this study, the relationship between IgG1, IgG2a, IgG2b, and IgG3 dose, infective inocula, and protection was investigated in a mouse model of Cryptococcus neoformans infection. The activity of each IgG subclass ranged from protective to disease-enhancing depending on both the Ab dose and infective inocula used. Enhanced dissemination to the brain was observed in mice given a high IgG2a dose and a relatively low inoculum. Ab administration had immunomodulatory effects, with cytokine expression in lung, brain, and spleen varying as a function of the infective inoculum Ab dose and IgG subclass. In vitro studies did not predict or explain the mechanism of in vivo prozone-like effects, because all isotypes were opsonic and elicited NO release from macrophages. IgG2a was most efficient in inducing a macrophage oxidative burst. These results reveal that an individual Ab can be protective, nonprotective, or disease-enhancing depending on its concentration relative to a challenge inoculum. Our findings have implications for the potential contribution of Ab responses to defense against microbial diseases because Ab-mediated immunity may be protective, nonprotective, or even deleterious to the host.     

Mouse genetic background is a major determinant of isotype-related differences for antibody-mediated protective efficacy against Cryptococcus neoformans

The protective efficacy of mAbs to Cryptococcus neoformans glucuronoxylomannan depends on Ab isotype. Previous studies in A/JCr and C57BL/6J mice showed relative protective efficacy of IgG1, IgG2a > IgG3. However, we now report that in C57BL/6J x 129/Sv mice, IgG3 is protective while IgG1 is not protective, with neither isotype being protective in 129/Sv mice. IgG1, IgG2a, and IgG3 had different effects on IFN-gamma expression in infected C57BL/6J x 129/Sv mice. IgG1-treated C57BL/6J x 129/Sv mice had significantly more pulmonary eosinophilia than IgG2a- and IgG3-treated C57BL/6J x 129/Sv mice. C. neoformans infection and Ab administration had different effects on FcgammaRI, FcgammaRII, and FcgammaRIII expression in C57BL/6J, 129/Sv, and C57BL/6J x 129/Sv mice. Our results indicate that the relative efficacy of Ab isotype function against C. neoformans is a function of the genetic background of the host and that IgG3-mediated protection in C57BL/6J x 129/Sv mice was associated with lower levels of IFN-gamma and fewer pulmonary eosinophils. The dependence of isotype efficacy on host genetics underscores a previously unsuspected complex relationship between the cellular and humoral arms of the adaptive immune response.     

HIV-1 envelope triggers polyclonal Ig class switch recombination through a CD40-independent mechanism involving BAFF and C-type lectin receptors

Switching from IgM to IgG and IgA is essential for antiviral immunity and requires engagement of CD40 on B cells by CD40L on CD4(+) T cells. HIV-1 is thought to impair CD40-dependent production of protective IgG and IgA by inducing progressive loss of CD4(+) T cells. Paradoxically, this humoral immunodeficiency is associated with B cell hyperactivation and increased production of nonprotective IgG and IgA that are either nonspecific or specific for HIV-1 envelope glycoproteins, including gp120. Nonspecific and gp120-specific IgG and IgA are sensitive to antiretroviral therapy and remain sustained in infected individuals with very few CD4(+) T cells. One interpretation is that some HIV-1 Ags elicit IgG and IgA class switch DNA recombination (CSR) in a CD40-independent fashion. We show that a subset of B cells binds gp120 through mannose C-type lectin receptors (MCLRs). In the presence of gp120, MCLR-expressing B cells up-regulate the CSR-inducing enzyme, activation-induced cytidine deaminase, and undergo CSR from IgM to IgG and IgA. CSR is further enhanced by IL-4 or IL-10, whereas Ab secretion requires a B cell-activating factor of the TNF family. This CD40L-related molecule is produced by monocytes upon CD4, CCR5, and CXCR4 engagement by gp120 and cooperates with IL-4 and IL-10 to up-regulate MCLRs on B cells. Thus, gp120 may elicit polyclonal IgG and IgA responses by linking the innate and adaptive immune systems through the B cell-activating factor of the TNF family. Chronic activation of B cells through this CD40-independent pathway could impair protective T cell-dependent Ab responses by inducing immune exhaustion.     

Role of L-ficolin/mannose-binding lectin-associated serine protease complexes in the opsonophagocytosis of type III group B streptococci

Serotype III group B streptococci (GBS) are a common cause of neonatal sepsis and meningitis. Although deficiency in maternal capsular polysaccharide (CPS)-specific IgG correlates with susceptibility of neonates to the GBS infection, serum deficient in CPS-specific IgG mediates significant opsonophagocytosis. This IgG-independent opsonophagocytosis requires activation of the complement pathway, a process requiring the presence of both Ca(2+) and Mg(2+), and is significantly reduced by chelating Ca(2+) with EGTA. In these studies, we defined a role of L-ficolin/mannose-binding lectin-associated serine protease (MASP) complexes in Ca(2+)-dependent, Ab-independent opsonophagocytosis of serotype III GBS. Incubation of GBS with affinity-purified L-ficolin/MASP complexes and C1q-depleted serum deficient in CPS-specific Ab supported opsonophagocytic killing, and this killing was inhibited by fluid-phase N-acetylglucosamine, the ligand for L-ficolin. Binding of L-ficolin was proportional to the CPS content of individual strains, and opsonophagocytic killing and C4 activation were inhibited by fluid-phase CPS, suggesting that L-ficolin binds to CPS. Sialic acid is known to inhibit alternative complement pathway activation, and, as expected, the bactericidal index (percentage of bacteria killed) for individual strains was inversely proportional to the sialic acid content of the CPS, and L-ficolin-initiated opsonophagocytic killing was significantly increased by addition of CPS-specific IgG2, which increased activation of the alternative pathway. We conclude that binding of L-ficolin/MASP complexes to the CPS generates C3 convertase C4b2a, which deposits C3b on GBS. C3b deposited by this lectin pathway forms alternative pathway C3 convertase C3bBb whose activity is enhanced by CPS-specific IgG2, leading to increased opsonophagocytic killing by further deposition of C3b on the GBS.     

Identification of novel Leishmania major antigens that elicit IgG2a response in resistant and susceptible mice

Experimental murine models with high, intermediate and low levels of genetically based susceptibility to Leishmania major infection reproduce almost entire spectrum of clinical manifestations of the human disease. There are increasing non-comparative studies on immune responses against isolated antigens of L. major in different murine strains. The aim of the present study was to find out whether there is an antigen that can induce protective immune response in resistant and susceptible murine strains. To do that, crude antigenic extract of procyclic and metacyclic promastigotes of L. major was prepared and subjected to SDS-PAGE electrophoresis. Western-blotting was used to search for antigen(s) capable of raising high antibody level of IgG2a versus IgG1 in the sera of both infected resistant and susceptible strains. Two novel antigens from metacyclic promastigotes of L. major (140 and 152 kDa) were potentially able to induce specific dominant IgG2a responses in BALB/c and C57BL/6 mice. The 2 antigens also reacted with IgG antibody of cutaneous leishmaniasis patients. We confirm that 140 and 152 kDa proteins of L. major promastigotes are inducing IgG production in mice and humans.     

The respiratory syncytial virus G protein conserved domain induces a persistent and protective antibody response in rodents

Respiratory syncytial virus (RSV) is an important cause of severe upper and lower respiratory disease in infants and in the elderly. There are 2 main RSV subtypes A and B. A recombinant vaccine was designed based on the central domain of the RSV-A attachment G protein which we had previously named G2Na (aa130-230). Here we evaluated immunogenicity, persistence of antibody (Ab) response and protective efficacy induced in rodents by: (i) G2Na fused to DT (Diphtheria toxin) fragments in cotton rats. DT fusion did not potentiate neutralizing Ab responses against RSV-A or cross-reactivity to RSV-B. (ii) G2Nb (aa130-230 of the RSV-B G protein) either fused to, or admixed with G2Na. G2Nb did not induce RSV-B-reactive Ab responses. (iii) G2Na at low doses. Two injections of 3 μg G2Na in Alum were sufficient to induce protective immune responses in mouse lungs, preventing RSV-A and greatly reducing RSV-B infections. In cotton rats, G2Na-induced RSV-reactive Ab and protective immunity against RSV-A challenge that persisted for at least 24 weeks. (iv) injecting RSV primed mice with a single dose of G2Na/Alum or G2Na/PLGA [poly(D,L-lactide-co-glycolide]. Despite the presence of pre-existing RSV-specific Abs, these formulations effectively boosted anti-RSV Ab titres and increased Ab titres persisted for at least 21 weeks. Affinity maturation of these Abs increased from day 28 to day 148. These data indicate that G2Na has potential as a component of an RSV vaccine formulation.     

Natural Killer Cell Sensing of Infected Cells Compensates for MyD88 Deficiency but Not IFN-I Activity in Resistance to Mouse Cytomegalovirus

In mice, plasmacytoid dendritic cells (pDC) and natural killer (NK) cells both contribute to resistance to systemic infections with herpes viruses including mouse Cytomegalovirus (MCMV). pDCs are the major source of type I IFN (IFN-I) during MCMV infection. This response requires pDC-intrinsic MyD88-dependent signaling by Toll-Like Receptors 7 and 9. Provided that they express appropriate recognition receptors such as Ly49H, NK cells can directly sense and kill MCMV-infected cells. The loss of any one of these responses increases susceptibility to infection. However, the relative importance of these antiviral immune responses and how they are related remain unclear. In humans, while IFN-I responses are essential, MyD88 is dispensable for antiviral immunity. Hence, a higher redundancy has been proposed in the mechanisms promoting protective immune responses against systemic infections by herpes viruses during natural infections in humans. It has been assumed, but not proven, that mice fail to mount protective MyD88-independent IFN-I responses. In humans, the mechanism that compensates MyD88 deficiency has not been elucidated. To address these issues, we compared resistance to MCMV infection and immune responses between mouse strains deficient for MyD88, the IFN-I receptor and/or Ly49H. We show that selective depletion of pDC or genetic deficiencies for MyD88 or TLR9 drastically decreased production of IFN-I, but not the protective antiviral responses. Moreover, MyD88, but not IFN-I receptor, deficiency could largely be compensated by Ly49H-mediated antiviral NK cell responses. Thus, contrary to the current dogma but consistent with the situation in humans, we conclude that, in mice, in our experimental settings, MyD88 is redundant for IFN-I responses and overall defense against a systemic herpes virus infection. Moreover, we identified direct NK cell sensing of infected cells as one mechanism able to compensate for MyD88 deficiency in mice. Similar mechanisms likely contribute to protect MyD88- or IRAK4-deficient patients from viral infections.     

Protective effects of anti-antiidiotypic IgE antibodies obtained from an IgE monoclonal antibody specific for a 26-kilodalton Schistosoma mansoni antigen

A rat IgE mAb specific for larval Ag (26 kDa, 56 kDa) has been shown to protect rats against Schistosoma mansoni infection. Immunizations of Lou/M rats performed with this IgE (Ab1) induced the production of antiidiotypic antibodies (Ab2). Moreover, after this Ab2 production, anti-antiidiotypic antibodies (Ab3) were revealed. The screening of Ab3 isotypes showed the presence of IgG Ab3 and more interestingly of IgE Ab3, i.e., the same isotype as Ab1. These IgE and IgG antibodies recognized predominantly the 26-kDa Ag and were cytotoxic for schistosomula in the presence of platelets for IgE Ab3 and eosinophils for IgG Ab3. Both IgE and IgG Ab3 conferred by passive transfer protective immunity to infected rats (up to 50%). Thus the immunization with an IgE mAb led in part to the production of Ab3 of the same isotype as Ab1. In conclusion, these results suggest that the isotype selection of the antibodies of the third generation (Ab3) might be influenced by the Ab1. The respective role of the idiotope and isotype of Ab1 in isotype regulation is discussed.     

Patients with Wiskott-Aldrich syndrome have normal IgG2 levels

The Wiskott-Aldrich Syndrome (WAS) in humans has a number of similarities to the immunodeficiencies found in CBA/N mice, including X-chromosome-linked inheritance, inability to produce antibodies to various carbohydrate antigens, susceptibility to various bacterial infections, and an imbalance in B lymphocyte subpopulations. Moreover, in both man and mice, IgG antibodies to polysaccharides are predominantly, but not exclusively, restricted to a single IgG subclass--IgG2 in man, and IgG3 in the mouse. Because CBA/N mice have a deficiency of IgG3 antibodies and because human IgG2 subclass deficiencies have been generally associated with inability to produce antibodies to carbohydrate antigens, it would seem likely that patients with WAS would have greatly reduced levels of IgG2. Quite to the contrary, the data presented here demonstrate that WAS patients have normal levels of the different IgG subclasses, including IgG2. Thus, inability to produce antibodies to carbohydrates is not always associated with IgG2 subclass deficiency.     

TLR9 signaling in B cells determines class switch recombination to IgG2a

Although IgG2a is the most potent Ab isotype in the host response to viral and bacterial infections, the regulation of class switch recombination to IgG2a in vivo is not yet well understood. Recognition of pathogen-associated molecular patterns by dendritic cells expressing TLRs, like TLR7, recognizing ssRNA, or TLR9, recognizing DNA rich in nonmethylated CG motifs (CpG), favors induction of Th1 responses. It is generally assumed that these Th1 responses are responsible for the TLR-mediated induction of IgG2a. Using virus-like particles loaded with CpGs, we show here that TLR9 ligands can directly stimulate B cells to undergo isotype switching to IgG2a. Unexpectedly, TLR9 expression in non-B cells did not affect isotype switching in the Ab response against virus-like particles. Thus, TLR9 can regulate isotype switching to IgG2a directly by interacting with B cells rather than indirectly by inducing Th1 responses.     

Critical role of T cell-dependent serum antibody, but not the gut-associated lymphoid tissue, for surviving acute mucosal infection with Citrobacter rodentium, an attaching and effacing pathogen

Citrobacter rodentium uses virulence factors similar to the enteropathogenic Escherichia coli to produce attaching and effacing lesions in the distal colon of mice. We used this infection model to determine components of adaptive immunity needed to survive infection. During acute infection, wild-type mice develop breaks across infected epithelial surfaces but resolve infection. Surprisingly, mice markedly deficient in mucosal lymphocyte populations from beta(7) integrin deficiency resolve infection, as do CD8alpha-/- or TCR-delta-/- mice. In contrast, CD4-/- or TCR-beta-/- mice develop polymicrobial sepsis and end-organ damage, and succumb during acute infection, despite epithelial damage similar to wild-type mice. B cell-deficient (MuMT-/-) or B and T cell-deficient (recombinase-activating gene 2-/-) mice develop severe pathology in colon and internal organs, and deteriorate rapidly during acute infection. Surviving mice develop robust Citrobacter-specific serum IgM responses during acute infection, whereas mice that succumb do not. However, CD4-/- mice receiving serum Igs from infected wild-type mice survive and clear the infection. Our data show that survival of apparently self-limited and luminal mucosal infections requires a systemic T cell-dependent Ab response against bacteria that enter through damaged mucosa. These findings have implications for understanding host defense against mucosal infections, including the pathogenesis of these diseases in immunocompromised populations.     

SAP is required for Th cell function and for immunity to influenza

Ab is a crucial component of protective immunity to infection, but Ab responses do not proceed normally when defects occur in a protein called signaling lymphocytic activation molecule-associated protein (SAP). To explain this Ab defect, we analyzed B cell and plasma cell responses under conditions of SAP deficiency. Our results demonstrate that SAP-deficient (SAP knockout (KO)) mice have a profound CD4 T cell-intrinsic defect in generating Ag-specific plasma cells following challenge with model Ags or influenza virus, resulting in low Ag-specific Ab titers. We also show that SAP is required in CD4 T cells for normal division and expansion of B cells. These B cell and plasma cell defects were observed during the expansion phase of the primary immune response, indicating early defects in Th cell activity. In fact, additional experiments revealed a nearly complete lack of T cell help for B cells in SAP KO mice. Our work suggests that the ability of SAP to promote T-dependent humoral immune responses is important for antiviral immunity because mice lacking SAP are unable to prevent high dose secondary influenza infection, and because passive transfer of IgG in immune serum from wild-type, but not SAP KO mice can protect mice from an otherwise lethal influenza infection. Overall, our results demonstrate that SAP is required in CD4 T cells for their ability to help B cell responses and promote influenza-specific immunity.     

Bacillus anthracis edema toxin acts as an adjuvant for mucosal immune responses to nasally administered vaccine antigens

Anthrax edema toxin (EdTx) is an AB-type toxin that binds to anthrax toxin receptors on target cells via the binding subunit, protective Ag (PA). Edema factor, the enzymatic A subunit of EdTx, is an adenylate cyclase. We found that nasal delivery of EdTx enhanced systemic immunity to nasally coadministered OVA and resulted in high OVA-specific plasma IgA and IgG (mainly IgG1 and IgG2b). The edema factor also enhanced immunity to the binding PA subunit itself and promoted high levels of plasma IgG and IgA responses as well as neutralizing PA Abs. Mice given OVA and EdTx also exhibited both PA- and OVA-specific IgA and IgG Ab responses in saliva as well as IgA Ab responses in vaginal washes. EdTx as adjuvant triggered OVA- and PA-specific + T cells which secreted IFN-gamma and selected Th2-type cytokines. The EdTx up-regulated costimulatory molecule expression by APCs but was less effective than cholera toxin for inducing IL-6 responses either by APCs in vitro or in nasal washes in vivo. Finally, nasally administered EdTx did not target CNS tissues and did not induce IL-1 mRNA responses in the nasopharyngeal-associated lymphoepithelial tissue or in the olfactory bulb epithelium. Thus, EdTx derivatives could represent an alternative to the ganglioside-binding enterotoxin adjuvants and provide new tools for inducing protective immunity to PA-based anthrax vaccines.     

Effective mucosal immunity to anthrax: neutralizing antibodies and Th cell responses following nasal immunization with protective antigen

Mucosal, but not parenteral, immunization induces immune responses in both systemic and secretory immune compartments. Thus, despite the reports that Abs to the protective Ag of anthrax (PA) have both anti-toxin and anti-spore activities, a vaccine administered parenterally, such as the aluminum-adsorbed anthrax vaccine, will most likely not induce the needed mucosal immunity to efficiently protect the initial site of infection with inhaled anthrax spores. We therefore took a nasal anthrax vaccine approach to attempt to induce protective immunity both at mucosal surfaces and in the peripheral immune compartment. Mice nasally immunized with recombinant PA (rPA) and cholera toxin (CT) as mucosal adjuvant developed high plasma PA-specific IgG Ab responses. Plasma IgA Abs as well as secretory IgA anti-PA Abs in saliva, nasal washes, and fecal extracts were also induced when a higher dose of rPA was used. The anti-PA IgG subclass responses to nasal rPA plus CT consisted of IgG1 and IgG2b Abs. A more balanced profile of IgG subclasses with IgG1, IgG2a, and IgG2b Abs was seen when rPA was given with a CpG oligodeoxynucleotide as adjuvant, suggesting a role for the adjuvants in the nasal rPA-induced immunity. The PA-specific CD4(+) T cells from mice nasally immunized with rPA and CT as adjuvant secreted low levels of CD4(+) Th1-type cytokines in vitro, but exhibited elevated IL-4, IL-5, IL-6, and IL-10 responses. The functional significance of the anti-PA Ab responses was established in an in vitro macrophage toxicity assay in which both plasma and mucosal secretions neutralized the lethal effects of Bacillus anthracis toxin.