Immunoglobulin A (IgA): molecular and cellular interactions involved in IgA biosynthesis and immune response

Polysaccharide kinase activity of human milk IgG antibodies

A small fraction of human milk IgG antibodies is shown to possess polysaccharide kinase activity for the first time. Unlike all known kinases, IgG antibodies can use as phosphate donor not only [gamma-(32)P]ATP, but also directly [(32)P]ortho-phosphate. Human milk IgGs therefore possess high affinity to ortho-phosphate (K(m) = 9-71 microM), which is a more effective substrate than ATP. IgG antibodies possessing polysaccharide kinase activity are yet another example of natural abzymes possessing not hydrolytic, but synthetic enzymatic activity.

IgM and IgA anti-erythrocyte autoantibodies induce anemia in a mouse model through multivalency-dependent hemagglutination but not through complement activation

By generating IgM and IgA switch variants of the 34-3C IgG2a anti-red blood cell (RBC) autoantibody, we evaluated the pathogenic activity of these 2 isotypes in view of the Fc-associated effector functions (ie, complement activation and polyvalency-dependent agglutination). We found that polymeric forms of 34-3C IgM and IgA anti-RBC autoantibody were as pathogenic as IgG2a, which was the most pathogenic among 4 different IgG subclasses, whereas their monomeric variants completely lacked pathogenic effects. Histological examination showed that 34-3C IgM and IgA autoantibodies caused anemia as a result of multivalency-dependent hemaggultination and subsequent sequestration of RBC in the spleen, in contrast to Fc receptor- and complement receptor-mediated erythrophagocytosis by Kupffer cells with IgG isotypes. In addition, the development of anemia induced by IgM and IgA isotypes of 34-3C antibody and by 2 additional IgM anti-RBC monoclonal autoantibodies was not inhibited at all in C3-deficient mice, indicating the lack of involvement of complement activation in the pathogenesis of IgM- and IgA-induced anemia. Our data demonstrate a remarkably high pathogenic potential of polymeric forms of IgM and IgA anti-RBC autoantibodies due to their ability to induce hemagglutination but completely independent of complement activation.

Influenza Virus Infection of the Murine Uterus: A New Model for Antiviral Immunity in the Female Reproductive Tract

Secretory IgA (S-IgA) mediates local immunity to influenza virus in the murine upper respiratory tract and may play an important role in local immunity to various microorganisms in the female reproductive tract as well. Although the presence of IgA in cervicovaginal or uterine secretions has been correlated with immunity to a number of pathogens, there has been no direct demonstration of the mediation of uterine antiviral immunity by S-IgA. Influenza virus, although not a normal pathogen of the reproductive tract, was used to develop a model for the investigation of mucosal immunity in the uterus. PR8 (H1N1) influenza virus injected into the ovarian bursa of BALB/c mice grew well, with peak titers between days 3 and 5. Intravenous injection of polymeric IgA anti-influenza virus monoclonal antibody before or 30 min after viral challenge protected mice against viral infection. We believe this work to be the first direct demonstration of S-IgA-mediated antiviral uterine immunity. It provides a model for further investigation of immunity in the female reproductive tract.

Effects of cyadox and olaquindox on intestinal mucosal immunity and on fecal shedding of Escherichia coli in piglets

A 2 x 3 factorial arrangement of treatments was used to determine the effects of olaquindox and cyadox on the intestinal mucosal immune response and on fecal shedding of Escherichia coli in Landrace x Large White barrows that had been orally given 10(10) cfu of E. coli (O139:K88). Factors included 1) E. coli inoculation or no inoculation, and 2) no antimicrobial, 100 mg of olaquindox/kg, and 100 mg of cyadox/kg in the basal diet, respectively. The effects of cyadox and olaquindox were assessed in terms of fecal shedding of E. coli, the number of intraepithelial lymphocytes (IEL), immunoglobulin A-positive cells (APC) in the intestinal lamina propria, and ADG. There was no difference in the fecal shedding of total E. coli or the inoculated E. coli between olaquindox-supplemented pigs and cyadox-supplemented pigs during the experiment. However, fecal shedding of the inoculated E. coli in olaquindox- or cyadox-supplemented pigs was less (P < 0.05) than that in nonsupplemented pigs. Escherichia coli inoculation increased IEL and APC in the jejunum and ileum, but olaquindox or cyadox decreased IEL and APC (P < 0.05). Jejunal APC in cyadox-supplemented pigs was less (P < 0.05) than that in olaquindox-supplemented pigs. Escherichia coli inoculation reduced (P < 0.05) ADG, whereas the supplementations improved ADG (P < 0.01) during the experiment. Average daily gain in cyadox-supplemented pigs was greater (P < 0.05) than that in olaquindox-supplemented pigs. The data indicated that olaquindox and cyadox reduced the number of intestinal E. coli and suppressed E. coli-induced immune activation, which might be responsible for the enhanced growth that was observed.

IgA and IgA-specific receptors in human disease: structural and functional insights into pathogenesis and therapeutic potential

IgA antibodies play an important role in humoral immunity. IgA is the predominant antibody in mucosal secretions and the second most prevalent in the serum. It occupies a unique position among human antibodies in that it can both trigger and suppress inflammatory responses, depending on the situation. Recent structural and functional studies have revealed details of the structure of IgA and its interaction with key cell-surface receptors. We look at the role IgA and IgA receptors (particularly FcalphaRI) play in the pathogenesis of diseases such as IgA nephropathy and other autoimmune conditions. Finally, we address the potential of IgA as a therapeutic tool to either trigger specific inflammatory responses to destroy target cells or suppress inflammatory responses in the case of autoimmune diseases, and the promise of mucosal vaccines for eliciting specific IgA responses to pathogens in mucosal environments.

Structural insights into antibody-mediated mucosal immunity

The mucosal regions of the body are responsible for defense against environmental pathogens. Particularly in the lumen of the gut, antibody-mediated immune responses are critical for preventing invasion by pathogens. In this chapter, we review structural studies that have illuminated various aspects of mucosal immunity. Crystal structures of IgA1-Fc and IgA-binding fragments of the polymeric immunoglobulin receptor and Fc alphaRI, combined with models of intact IgA and IgM from solution scattering studies, reveal potential mechanisms for immune exclusion and induction of inflammatory responses. Other recent structures yield insights into bacterial mechanisms for evasion of the host immune response.

Sulphasalazine inhibits human antigen-specific immune responses in vivo

OBJECTIVE

To study the effects of the antirheumatic drug sulphasalazine (SASP) on the immune system by analysing systemic and gut-associated immune responses.

METHODS

A total of 23 healthy volunteers were treated with either SASP or placebo for 5 weeks in a double-blind fashion and immunised 2 weeks after the initiation of treatment. Specific immune responses were triggered by subcutaneous immunisation with tetanus toxoid and by peroral immunisation with inactivated influenza vaccine. The effects of treatment on specific immunity to tetanus and influenza were evaluated by enzyme-linked immunospot assay quantifying the number of circulating specific and total antibody-producing cells (spot-forming cells (SFC)) at 6, 8 and 10 days after immunisation.

RESULTS

An immunosuppressive effect of SASP on systemic immune response was observed with a decrease in the total number of IgG-SFC, IgG anti-tetanus SFC and IgG anti-tetanus antibody levels in serum. SASP also exerted an immunosuppressive effect on the mucosa-associated immune system as seen from its down-regulating effect on the total number of circulating IgA SFC.

CONCLUSIONS

These data show firstly that SASP exerts an immunosuppressive effect on defined immune responses to immunisation in vivo, and secondly that both mucosa-associated and systemic immunity are affected by SASP treatment.

Antimicrobial defence mechanisms of the human parotid duct

The parotid duct transports saliva from the gland into the oral cavity. However, its immune response properties, along with the secretion and moistening principles of the duct, have not yet been fully investigated. These properties may play an important role in protecting the parotid gland from infection and also prevent development of sialodocholithiasis, as the parotid duct -- in contrast to the submandibular salivary duct -- is often free of duct concrements. Up to now, only the parotid gland has been investigated, without regard to its duct. The present study analyses the structures of the parotid duct in their relations to antimicrobial defence mechanisms and rheological properties. Investigations were performed on 23 parotid ducts using histological, histochemical and immunohistochemical methods. Epithelial and goblet cells of the parotid duct synthesize a complex mucous layer that covers the epithelium. The viscosity is influenced by secreted mucins and TFF peptides. This layer contains carbohydrates including N-acetyl-glucosamine, N-acetyl-galactosamine, galactose, mannose, fucose and sialic acids. The lamina propria contains granulocytes, T lymphocytes and macrophages. IgA, produced by plasma cells in the subepithelial layer, is frequently integrated in the secretory product. Synthesized mucins, TFF peptides, carbohydrates and immunoglobulins form a complex layer that can be expected to prohibit infection and enables salivary flow. Our study demonstrates that the steady secretion of the parotid gland, together with the ductal cellular and biochemical immune protection system, is likely to thwart ascending infections in the parotid duct and gland.

Contribution of polymeric immunoglobulin receptor to regulation of intestinal inflammation in dextran sulfate sodium-induced colitis

BACKGROUND

Inflammatory bowel disease (IBD) affects approximately 4 million people worldwide and can be caused by dysregulated mucosal immune responses to the intestinal commensal microflora. Immunoglobulin A (IgA) is considered to be the principal antibody in intestinal secretions and functions to prevent commensals and pathogenic organisms from gaining access to epithelial cell surfaces. Immunoglobulin A deficiency in humans has been associated with celiac disease and ulcerative colitis. However, the precise role of IgA in the pathogenesis of these disorders is yet to be fully understood.

METHODS

Mice with a targeted disruption in IgA production (IgA(-/-) mice) and polymeric immunoglobulin receptor (pIgR(-/-) mice) were analyzed for the contribution of secretory immunity in the pathogenesis of dextran sulfate sodium (2.5%)-induced colitis.

RESULTS

It was found that dextran sulfate sodium-treated pIgR(-/-) mice displayed greater loss of bodyweight and had severe clinical illness compared to similarly treated IgA(-/-) mice and wild-type animals. Additionally, colonic tissues from the pIgR(-/-) mice exhibited progressively and significantly greater degrees of mucosal edema, ulceration, crypt abscesses and macrophage infiltration when compared to similarly treated IgA(-/-) mice and wild-type animals.

CONCLUSIONS

The results indicate that secretory immunoglobulins contribute to protection of the colonic mucosa against dextran sulfate sodium-induced epithelial injury, although the isotype of the secretory immunoglobulin (IgA or IgM) may not be a decisive factor in such protection. Collectively, the pIgR and/or the secretory component are important for the maintenance of epithelial integrity and mucosal homeostasis in the colonic epithelium.

Albumin infusion after reperfusion prevents gut ischemia-reperfusion-induced gut-associated lymphoid tissue atrophy

BACKGROUND

Our recent study clarified that gut ischemia-reperfusion (I/R) causes gut-associated lymphoid tissue (GALT) mass atrophy, a possible mechanism for increased morbidity of infectious complications after severe surgical insults. Because albumin administration reportedly reduces hemorrhagic shock-induced lung injury, we hypothesized that albumin treatment prevents GALT atrophy due to gut I/R.

METHODS

Male mice (n = 37) were randomized to albumin, normal saline, and sham groups. All groups underwent jugular vein catheter insertion. The albumin and normal saline groups underwent 75-minute occlusion of the superior mesenteric artery. During gut ischemia, all mice received normal saline infusions at 1.0 mL/h. The albumin group was given 5% bovine serum albumin in normal saline at 1.0 mL/h for 60 minutes after reperfusion, whereas the normal saline group received 0.9% sodium chloride at 1.0 mL/h. The sham group underwent laparotomy only. Mice were killed on day 1 or 7, and the entire small intestine was harvested. GALT lymphocytes were isolated and counted. Their phenotypes (alphabetaTCR, gammadeltaTCR, CD4, CD8, B220) were determined by flow cytometry.

RESULTS

On day 1, the gut I/R groups showed significantly lower total lymphocyte and B cell numbers in Peyer's patches and the lamina propria than the sham group. However, the albumin infusion partially but significantly restored these cell numbers. On day 7, there were no significant differences in any of the parameters measured among the 3 groups.

CONCLUSIONS

Albumin infusion after a gut ischemic insult may maintain gut immunity by preventing GALT atrophy.

Nanoparticles as potential oral delivery systems of proteins and vaccines: a mechanistic approach

Peptides and proteins remain poorly bioavailable upon oral administration. One of the most promising strategies to improve their oral delivery relies on their association with colloidal carriers, e.g. polymeric nanoparticles, stable in gastrointestinal tract, protective for encapsulated substances and able to modulate physicochemical characteristics, drug release and biological behavior. The mechanisms of transport of these nanoparticles across intestinal mucosa are reviewed. In particular, the influence of size and surface properties on their non-specific uptake or their targeted uptake by enterocytes and/or M cells is discussed. Enhancement of their uptake by appropriate cells, i.e. M cells by (i) modeling surface properties to optimize access to and transport by M cells (ii) identifying surface markers specific to human M cell allowing targeting to M cells and nanoparticles transcytosis is illustrated. Encouraging results upon in vivo testing are reported but low bioavailability and lack of control on absorbed dose slow down products development. Vaccines are certainly the most promising applications for orally delivered nanoparticles.

Olaquindox and cyadox stimulate growth and decrease intestinal mucosal immunity of piglets orally inoculated with Escherichia coli

One hundred and fifty piglets were randomly allotted to one of six treatments to determine the effects of olaquindox and cyadox on growth and intestinal immune response including the number of intraepithelial lymphocytes and immunoglobulin A secreting cells (ASCs) during the three-week period. A 2 x 3 factorial arrangement of treatments was employed with the following factors: (1) Escherichia coli (O(139):K(88), 10(10) CFU) inoculation or control and (2) no antimicrobials, 100 mg/kg olaquindox and 100 mg/kg cyadox in the basal diet respectively. The antimicrobial supplementations improved (p < 0.01) average daily gain and feed conversion ratio (FCR) during the experiment. Average daily gain and FCR in the cyadox-supplemented pigs were higher (p < 0.05) than those in the olaquindox-supplemented pigs. Intraepithelial lymphocytes and ASCs decreased (p < 0.05) when the diets were supplemented. Jejunal ASCs in the cyadox-supplemented pigs were lower (p < 0.05) than those in the olaquindox-supplemented pigs. Olaquindox and cyadox suppressed E. coli-induced intestinal immune activation, which may be involved in the observed growth promotion.

Analysis of Antigen-Specific and Naturally Occurring IgM and IgA Steady-State Levels in J-Chain Negative C57BL/6 Mice

Naturally occurring IgM and IgA levels are remarkably stable between different individuals. In mice lacking joining chain (J-chain), the steady-state levels of IgM are reduced, while IgA levels are elevated. We have here analysed the IgM and IgA responses as well as the regulation of naturally occurring antibodies in mice that delete all J-chain expressing B cells (JDTA mice) and have been back-crossed to C57BL/6 mice. The IgM response to a T-cell-dependent antigen was reduced in JDTA mice but still easily detectable. In contrast, a very pronounced primary IgA response could be detected in JDTA mice while wild type controls showed no detectable primary IgA response. With regard to naturally occurring antibodies, bone marrow chimeras between JDTA and control C57BL/6 mice had a donor cell phenotype with regard to serum IgM and IgA. Mixed bone marrow chimeras had an intermediate phenotype, indicating that the naturally occurring antibody IgM and IgA levels are B-cell autonomous and not subjected to feed-back control. This was confirmed by transfer of the dominant naturally occurring IgM/IgA phenotype to the recipient by peritoneal exudate cells.

Human milk antibodies with polysaccharide kinase activity

It was shown for the first time that a small fraction of milk secretory IgA (sIgA) is tightly bound to oligosaccharides (oligoSACs) and polysaccharides (polySACs). The ability of sIgA to phosphorylate oligo- and polysaccharides was shown to be an intrinsic property of this antibody. In contrast to known kinases, sIgAs with polysaccharide kinase activity can transfer phosphoryl group to oligo- and polysaccharides not only from [gamma-(32)P]ATP but can also use [(32)P]orthophosphate as a substrate of phosphorylation reaction. An extremely unusual property of polysaccharide kinase Abs is their high affinity for orthophosphate (K(m) = 15-77 microM), and orthophosphate is a better substrate than ATP. Two first examples of natural abzymes (Abzs) with synthetic activity were milk sIgA with protein and lipid kinase activities. Polysaccharide kinase sIgA of human milk is the third example of natural antibodies (Abs) with synthetic activity.

Persorption of Luminal Antigenic Molecule and Its Specific Antibody via Apoptotic Epithelial Cells of Intestinal Villi and Peyer's Patches into Peripheral Blood in Rats

The possibility of persorption of bovine serum albumin (BSA) molecules from mucous epithelial cells and its mechanism were investigated in rats orally pre-immunized by BSA for 14 consecutive days. In the small and large intestines, both the BSA antigen (BSA-Ag) and its specific antibody (SpAb) were absorbed by the epithelial cells at the late apoptotic stage (ApoEp), and were subsequently transcytosed by membranes of the small vesicles. The basal cytoplasms containing highly-concentrated BSA-Ag and SpAb were occasionally fragmented into small cytoplasmic droplets that were secreted into the lamina propria. In Peyer's patches, both BSA-Ag and SpAb were more actively absorbed and transcytosed toward the dome area by the ApoEp of the dome apex than by the M cells. BSA-Ag and SpAb were finally persorbed into the portal blood and lymph, but were never secreted into the bile. They were also engulfed by macrophage-like cells in the villous lamina propria, mesenteric lymph node and spleen, and by hepatocytes in the liver. These findings suggest that sensitized soluble luminal antigens are taken up by ApoEp in the small intestine and are finally persorbed into the peripheral blood. The uptake of luminal antigen might be mediated by its luminal SpAb.

Decision criteria for resolving isotype switching conflicts by B cells

Isotype switching by B cells is highly regulated by a group of cytokines including IL-4, IFN-gamma and TGF-beta. A B cell can only express one isotype at a time; however, during an immune response it may be exposed to combinations of stimuli that provide it with conflicting switching instructions. To determine how such cytokine-induced isotype switch conflicts would be resolved, the responses of B cells exposed to multiple cytokines were investigated. To eliminate complications arising from simultaneous effects of switching cytokines on proliferation, division number was used as a reference framework to monitor switching rate. The results show a clear hierarchy in which IFN-gamma is dominant over IL-4, and both IL-4 and IFN-gamma are dominant over TGF-beta. These studies reveal how B cells possess a set of logical decision criteria for dealing with pathogens that invoke a range of different stimuli.

Secretory IgA induces antigen-independent eosinophil survival and cytokine production without inducing effector functions

BACKGROUND

Eosinophils in human beings reside in tissues, especially the mucosal tissues of the gastrointestinal tract and inflamed airways. Secretory IgA (S-IgA) is the predominant antibody secreted by these tissues and likely plays a role in the innate immune response.

OBJECTIVE

Because eosinophils and S-IgA are often colocalized in mucosal tissues, we examined the potential regulatory effects of S-IgA without antigens on survival, gene expression, and effector functions of human eosinophils.

METHODS

Eosinophils were incubated with S-IgA in solution without antigens (soluble S-IgA) or with S-IgA immobilized to mimic multivalent antigen cross-linking. Eosinophil activation was monitored by superoxide anion generation and degranulation. Survival was assessed between 24 and 96 hours. Gene and protein expression were examined by microarray and ELISA. Eosinophil lysates were examined by immunoblot for extracellular signal-regulated kinase (ERK) phosphorylation.

RESULTS

Immobilized S-IgA stimulated eosinophil superoxide production and degranulation; soluble S-IgA did not. Although immobilized S-IgA inhibited eosinophil survival in vitro, soluble S-IgA enhanced survival; this involved autocrine production of GM-CSF. Soluble S-IgA without antigens induced increases in mRNA levels of various cytokines, chemokines, signal transduction molecules, antiapoptotic factors, and cell surface markers. By using ELISA, we confirmed protein expression of selected mediators. Eosinophil interaction with soluble S-IgA likely involves FcalphaRI (CD89) and ERK pathway activation.

CONCLUSION

Secretory IgA without multivalent antigens may regulate survival and gene expression of eosinophils. Eosinophils in mucosal tissues can be either primed for action (cytokine production and survival) or fully activated (degranulation and superoxide release) by different forms of S-IgA.

Oral tolerance

Multiple mechanisms of tolerance are induced by oral antigen. Low doses favor active suppression, whereas higher doses favor clonal anergy/deletion. Oral antigen induces T-helper 2 [interleukin (IL)-4/IL-10] and Th3 [transforming growth factor (TGF)-beta] T cells plus CD4+CD25+ regulatory cells and latency-associated peptide+ T cells. Induction of oral tolerance is enhanced by IL-4, IL-10, anti-IL-12, TGF-beta, cholera toxin B subunit, Flt-3 ligand, and anti-CD40 ligand. Oral (and nasal) antigen administration suppresses animal models of autoimmune diseases including experimental autoimmune encephalitis, uveitis, thyroiditis, myasthenia, arthritis, and diabetes in the non-obese diabetic (NOD) mouse, plus non-autoimmune diseases such as asthma, atherosclerosis, graft rejection, allergy, colitis, stroke, and models of Alzheimer's disease. Oral tolerance has been tested in human autoimmune diseases including multiple sclerosis (MS), arthritis, uveitis, and diabetes and in allergy, contact sensitivity to dinitrochlorobenzene (DNCB), and nickel allergy. Although positive results have been observed in phase II trials, no effect was observed in phase III trials of CII in rheumatoid arthritis or oral myelin and glatiramer acetate (GA) in MS. Large placebo effects were observed, and new trials of oral GA are underway. Oral insulin has recently been shown to delay onset of diabetes in at-risk populations, and confirmatory trials of oral insulin are being planned. Mucosal tolerance is an attractive approach for treatment of autoimmune and inflammatory diseases because of lack of toxicity, ease of administration over time, and antigen-specific mechanisms of action. The successful application of oral tolerance for the treatment of human diseases will depend on dose, developing immune markers to assess immunologic effects, route (nasal versus oral), formulation, mucosal adjuvants, combination therapy, and early therapy.

Mucosal B cells: phenotypic characteristics, transcriptional regulation, and homing properties

Mucosal antibody defense depends on a complex cooperation between local B cells and secretory epithelia. Mucosa-associated lymphoid tissue gives rise to B cells with striking J-chain expression that are seeded to secretory effector sites. Such preferential homing constitutes the biological basis for local production of polymeric immunoglobulin A (pIgA) and pentameric IgM with high affinity to the epithelial pIg receptor that readily can export these antibodies to the mucosal surface. This ultimate functional goal of mucosal B-cell differentiation appears to explain why the J chain is also expressed by IgG- and IgD-producing plasma cells (PCs) occurring at secretory tissue sites; these immunocytes may be considered as 'spin-offs' from early effector clones that through class switch are on their way to pIgA production. Abundant evidence supports the notion that intestinal PCs are largely derived from B cells initially activated in gut-associated lymphoid tissue (GALT). Nevertheless, insufficient knowledge exists concerning the relative importance of M cells, major histocompatibility complex class II-expressing epithelial cells, and professional antigen-presenting cells for the uptake, processing, and presentation of luminal antigens in GALT to accomplish the extensive and sustained priming and expansion of mucosal B cells. Likewise, it is unclear how the germinal center reaction in GALT so strikingly can promote class switch to IgA and expression of J chain. Although B-cell migration from GALT to the intestinal lamina propria is guided by rather well-defined adhesion molecules and chemokines/chemokine receptors, the cues directing preferential homing to different segments of the gut require better definition. This is even more so for the molecules involved in homing of mucosal B cells to secretory effector sites beyond the gut, and in this respect, the role of Waldever's ring (including the palatine tonsils and adenoids) as a regional inductive tissue needs further characterization. Data suggest a remarkable compartmentalization of the mucosal immune system that must be taken into account in the development of effective local vaccines to protect specifically the airways, eyes, oral cavity, small and large intestines, and urogenital tract.

Mucosal immunoglobulins

Due to their vast surface area, the mucosal surfaces of the body represent a major site of potential attack by invading pathogens. The secretions that bathe mucosal surfaces contain significant levels of immunoglobulins (Igs), which play key roles in immune defense of these surfaces. IgA is the predominant antibody class in many external secretions and has many functional attributes, both direct and indirect, that serve to prevent infective agents such as bacteria and viruses from breaching the mucosal barrier. This review details current understanding of the structural and functional characteristics of IgA, including interaction with specific receptors (such as Fc(alpha)RI, Fc(alpha)/microR, and CD71) and presents examples of the means by which certain pathogens circumvent the protective properties of this important Ig.

Oral immunization with a shiga toxin B subunit::rotavirus NSP490 fusion protein protects mice against gastroenteritis

A fusion protein containing the shiga toxin-1 B subunit (STB) linked to a 90 amino acid peptide (aa residues 86--175) from simian rotavirus (SA--11) nonstructural protein NSP4 was synthesized in Escherichia coli. Mice orally inoculated with 60 microg of STB::NSP4(90) fusion protein per dose generated higher humoral and intestinal antibody titers than mice inoculated with 30 microg of NSP4 alone. Serum anti-NSP4 IgG2a isotype titers were substantially greater than IgG1 titers, suggesting a dominant Th1 immune response. ELISA measurement of cytokines secreted from splenocytes isolated from immunized mice confirmed the STB::NSP4(90) fusion protein stimulation of a strong Th1 cell mediated immune response. Diarrhea in SA-11 rotavirus challenged neonates suckling from STB::NSP4 immunized dams was significantly reduced in severity and duration in comparison with virus challenged neonates from unimmunized mice. Together, our experiments demonstrate for the first time that the shiga toxin B subunit provides ligand mediated delivery of virus antigens to the gut-associated lymphoid tissues for enhanced stimulation of humoral and cellular responses against rotavirus gastroenteritis.

Mucosal immunization with a ricin toxin B subunit-rotavirus NSP4 fusion protein stimulates a Th1 lymphocyte response

The castor-oil plant Ricinus communis A-B dimeric toxin B subunit (RTB) was genetically linked at its N-terminus with a 90 amino acid peptide from simian rotavirus SA-11 non-structural protein NSP4(90) and produced in Escherichia coli BL21 cells. Biologically active recombinant NSP4(90)-RTB fusion protein was shown to bind glycoprotein asialofetuin receptor molecules in an in vitro enzyme-linked immunosorbent assay (ELISA). Oral inoculation of the purified NSP4(90)-RTB ligand-antigen fusion protein delivered the chimeric protein to intestinal epidermal cells for mucosal immunization against rotavirus infection. Mice fed the NSP4(90)-RTB fusion protein generated higher humoral and intestinal antibody titers than mice inoculated with NSP4(90) alone. Titers of serum IgG2a antibodies were significantly higher than IgG1 titers suggesting a dominant Th1 lymphocyte immune response. ELISA measurement of cytokines secreted from splenocyte isolated from immunized mice confirmed NSP4(90)-RTB fusion protein stimulates a strong Th1 cell-mediated immune response. The experimental results demonstrate that the ricin toxin B subunit N-terminus can be used as a site for delivery of virus antigens to the gut associated lymphoid tissues for RTB-mediated immune stimulation of antiviral mucosal immune responses.

Morphological analysis of the relation between immunoglobulin A production in the small intestine and the enteric nervous system

To investigate the relation between the enteric nervous system and immunocytes, fecal immunoglobulin (Ig) A and the distribution of IgA-positive cells close to nerve fibers in the lamina propria around the crypts of the small intestine were examined after intraperitoneal injection of lipopolysaccharides (LPS). In mice, IgA in the feces 1 h (LPS1) and 6 h (LPS6) after LPS injection increased compared to that in the control group. In the ileum lamina propria of the LPS1 group, the number of IgA-positive cells close to the epithelial basement membrane was increased. In the LPS6 group, on the other hand, there was a significant increase in the number of IgA-positive cells close to both the basement membrane and the nerve fibers. Our data suggest that LPS induced an increase in the number of IgA-positive cells migrating to the nerve fibers, and that migration to the nerve fibers is as important as migration to the basement membrane for IgA production.

Microencapsulated subunit vaccine approach to enterotoxigenic Escherichia coli and other mucosal pathogens

Infections of the intestinal, urogenital, and respiratory tracts are serious health problems worldwide from both a morbidity and mortality perspective. Mucosal pathogens attach to surfaces of mucosa as a prerequisite for colonization and subsequent pathogenesis. By expressing various surface adhesins (colonization factors, CF) they are able to bind to specific mucosal receptors. Enterotoxigenic Escherichia coli (ETEC) can express numerous CF that allow them to attach to a variety of hosts. Mucosal immunity directed against pathogenic microorganisms is critical in host protection with secretory IgA being particularly important in preventing microoganisms from colonizing host cells. M cells likewise have an important immunological function in the small intestines by binding and transporting antigens to lymphocytes and macrophages thus enhancing the immune response. The use of subunit vaccines, such as antigen encapsulated microspheres, can act to effectively deliver specific antigens so as to optimize their immunological response. With the threat of bioterrorism becoming a reality in recent years, the miroencapsulation of antigens from potential bioterrorist agents may be an effective method of delivery so as to induce a level of protection in at risk individuals. The encapsulation of ETEC colonization factors in microspheres and their subsequent administration in small animals and humans has been conducted for many years. Evidence suggests that this type of delivery system for ETEC antigens may enhance their immunogenicity and provide protection against this microorganism.

Mucosal immunity and tolerance in the elderly

Age-associated dysregulation of the immune system of the gastrointestinal (GI) tract has been well documented for both secretory (S)-IgA immunity and oral tolerance. Thus, impaired antigen-specific Ab responses in aged animals and the elderly have been reported. Further, it has been shown that gut-associated lymphoreticular tissue (GALT) mediated immune responses are more susceptible to aging than are lymphoid tissues involved in peripheral immunity. Aging also impairs oral tolerance, which may be of central importance for maintaining GI homeostasis. Thus, as early as 6-8-month-old mice failed to establish systemic unresponsiveness to orally introduced antigens. Despite these studies, the precise mechanisms for impaired GI tract immune system responses remain unclear. The evidence of reduced sizes of Peyer's patches through aging suggests that age-associated mucosal dysregulation may be the result of mucosal inductive tissue dysfunction. Indeed, the frequencies of naive CD4+ T cells and dendritic cells (DCs) in Peyer's patches of aged mice were reduced and this led to a lack of essential cytokine synthesis for the induction of either S-IgA immunity or oral tolerance.

Fimbriae of enterotoxigenic Escherichia coli function as a mucosal carrier for a coupled heterologous antigen

Receptor-mediated uptake of orally administered antigen can lead to an antigen-specific immune response, whereas oral administration of most other non-replicating soluble antigens results in the induction of oral tolerance. In the present study, it is shown that fimbriae purified from an F4(K88)(+) enterotoxigenic Escherichia coli strain can function as a mucosal carrier molecule for the model antigen human serum albumin (HSA). Glutaraldehyde-coupled F4/HSA conjugates were able to bind F4 receptor positive (F4R(+)) enterocytes, but not to F4R(-) enterocytes. Moreover, oral immunization of F4R(+) pigs with F4/HSA conjugates induced a HSA-specific immune response, whereas oral immunization with HSA/HSA conjugates did not. This mucosal carrier function of F4 fimbriae was improved following oral co-administration of the F4/HSA conjugates with the mucosal adjuvant cholera toxin (CT) to F4R(+) pigs, since both humoral and cellular HSA-specific responses were significantly increased. In comparison with F4R(+) pigs, the HSA-specific response was reduced following oral F4/HSA+CT immunization of F4R(-) pigs. This indicates that F4 fimbriae as mucosal carrier and CT as adjuvant synergistically improve the induction of a HSA-specific immune response following oral immunization of pigs. These results could open new perspectives in the development of vaccines against enteropathogens.

MAINTENANCE OF SERUM ANTIBODY LEVELS

In vertebrates, serum antibodies are an essential component of innate and adaptive immunity and immunological memory. They also can contribute significantly to immunopathology. Their composition is the result of tightly regulated differentiation of B lymphocytes into antibody-secreting plasma blasts and plasma cells. The survival of antibody-secreting cells determines their contribution to the immune response in which they were generated and to long-lasting immunity, as provided by stable serum antibody levels. Short-lived plasma blasts and/or plasma cells secrete antibodies for a reactive immune response. Short-lived plasma blasts can become long-lived plasma cells, probably by competition with preexisting plasma cells for occupation of a limited number of survival niches in the body, in a process not yet fully understood. Limitation of the number of long-lived plasma cells allows the immune system to maintain a stable humoral immunological memory over long periods, to react to new pathogenic challenges, and to adapt the humoral memory in response to these antigens.

Synthetic double-stranded RNA poly(I:C) combined with mucosal vaccine protects against influenza virus infection

The mucosal adjuvant effect of synthetic double-stranded RNA polyriboinosinic polyribocytidylic acid [poly(I:C)] against influenza virus was examined under intranasal coadministration with inactivated hemagglutinin (HA) vaccine in BALB/c mice and was shown to have a protective effect against both nasal-restricted infection and lethal lung infection. Intranasal administration of vaccine from PR8 (H1N1) with poly(I:C) induced a high anti-HA immunoglobulin A (IgA) response in the nasal wash and IgG antibody response in the serum, while vaccination without poly(I:C) induced little response. Intracerebral injection confirmed the safety of poly(I:C). In addition, we demonstrated that administration of poly(I:C) with either A/Beijing (H1N1) or A/Yamagata (H1N1) vaccine conferred complete protection against PR8 challenge in this mouse nasal infection model, suggesting that poly(I:C) possessed cross-protection ability against variant viruses. To investigate the mechanism of the protective effect of poly(I:C), mRNA levels of Toll-like receptors and cytokines were examined in the nasal-associated lymphoid tissue after vaccination or virus challenge. Intranasal administration of HA vaccine with poly(I:C) up-regulated expression of Toll-like receptor 3 and alpha/beta interferons as well as Th1- and Th2-related cytokines. We propose that poly(I:C) is a new effective intranasal adjuvant for influenza virus vaccine.

Protection against influenza virus infection by intranasal administration of hemagglutinin vaccine with chitin microparticles as an adjuvant

Chitin in the form of microparticles (chitin microparticles, CMP) has been demonstrated to be a potent stimulator of macrophages, promoting T-helper-1 (Th1) activation and cytokine response. In order to examine the mucosal adjuvant effect of CMP co-administered with influenza hemagglutinin (HA) vaccine against influenza infection, CMP were intranasally co-administered with influenza HA vaccine prepared from PR8 (H1N1) virus. Inoculation of the vaccine with CMP induced primary and secondary anti-HA IgA responses in the nasal wash and anti-HA IgG responses in the serum, which were significantly higher than those of nasal vaccination without CMP, and provided a complete protection against a homologous influenza virus challenge in the nasal infection influenza model. In addition, CMP-based immunization using A/Yamagata (H1N1) and A/Guizhou (H3N2) induced PR8 HA-reactive IgA in the nasal washes and specific-IgG in the serum. The immunization with A/Yamagata and CMP resulted in complete protection against a PR8 (H1N1) challenge in A/Yamagata (H1N1)-vaccinated mice, while that with A/Guizhou (H3N2) and CMP exhibited a 100-fold reduction of nasal virus titer, demonstrating the cross-protective effect of CMP and influenza vaccine. It is suggested that CMP provide a safe and effective adjuvant for nasal vaccination with inactivated influenza vaccine.

Immunoenhancing effects of a new probiotic strain, Lactobacillus fermentum PL9005

The immunoenhancing effects of Lactobacillus fermentum PL9005 were assessed via mouse intragastric inoculation. The number of immunoglobulin A-positive cells in the small intestine, CD4+ T lymphocytes in the peripheral blood, and the lymphocyte proliferation response to mitogen stimulation (lipopolysaccharide) increased in mice fed L. fermentum PL9005. The lactic acid concentration also increased dose dependently in the small intestine of mice fed L. fermentum PL9005. No differences were found in body weight, food intake, and clinical signs between mice fed L. fermentum PL9005 and the control group. Results indicated that L. fermentum PL9005 is a probiotic with immunoenhancing properties.

Antibody processing and engineering in plants, and new strategies for vaccine production

The use of transgenic plants for the production of recombinant proteins is not a universal solution for all proteins. The choice of this expression system depends very much on the type of protein and its applications. Many proteins will best be made by conventional microbial fermentation, similarly, we are already identifying proteins where plants represent the only practical option for one reason or another. It will be important to understand better the cellular mechanisms of protein folding, assembly and processing in plants, in order to maximise the potential of transgenic plants as a protein production system. One of the main advantages that plants offer is that they are higher eukaryotic organisms with an endomembrane system. Therefore, they fold and assemble recombinant proteins using protein chaperones that are homologous to those in mammalian cells, and they perform post-translational modifications. This allows, for example, the expression of monoclonal antibodies, first described in 1989, as well as a range of other types of immunoglobulin molecules and multimeric complexes.

Novel approaches for the induction of T helper 1 (Th1)- or Th2-type mucosal and parenteral immune responses

Mucosal surfaces are constantly challenged by micro-organisms and are protected by an integrated component of the immune system called mucosa-associated lymphoreticular tissue (MALT). The immune responses elicited at the mucosal level are regulated by T-helper (Th) cells and involve secretory IgA (S-IgA) antibodies (Abs) and cytotoxic T-lymphocytes (CTLs). Mucosal immunisation has the advantage over parenteral immunisation, of inducing S-IgA Abs and of conferring protection at both the mucosal and parenteral levels; however, administration of soluble antigens through a mucosal route very seldom results in significant mucosal and systemic immune responses. Therefore, appropriate mucosal adjuvants, recombinant bacterial and viral vectors and delivery systems have been developed to increase the immunogenicity of vaccine antigens and to preferentially induce antigen-specific T-helper (Th)1- or Th2-type responses, which in turn result in polarised effector immune responses. Understanding the mechanisms underlying Th1- and Th2-type developmental pathways and the ability of novel mucosal adjuvants and delivery systems to target the desired Th1- or Th2-type immune response would help to design effective mucosal vaccines, inducing predominant cell-mediated or humoral responses.

Study of humoral immunity to commensal oral bacteria in human infants demonstrates the presence of secretory immunoglobulin A antibodies reactive with Actinomyces naeslundii genospecies 1 and 2 ribotypes

The mouths of three human infants were examined from birth to age 2 years to detect colonization of Actinomyces naeslundii genospecies 1 and 2. These bacteria did not colonize until after tooth eruption. The diversity of posteruption isolates was determined by ribotyping. Using immunoblotting and enzyme-linked immunosorbent assay, we determined the reactivity of secretory immunoglobulin A (SIgA) antibodies in saliva samples collected from each infant before and after colonization against cell wall proteins from their own A. naeslundii strains and carbohydrates from standard A. naeslundii genospecies 1 and 2 strains. A. naeslundii genospecies 1 and 2 carbohydrate-reactive SIgA antibodies were not detected in any saliva sample. However, SIgA antibodies reactive with cell wall proteins were present in saliva before these bacteria colonized the mouth. These antibodies could be almost completely removed by absorption with A. odontolyticus, a species known to colonize the human mouth shortly after birth. However, after colonization by A. naeslundii genospecies 1 and 2, specific antibodies were induced that could not be removed by absorption with A. odontolyticus. Cluster analysis of the patterns of reactivity of postcolonization salivary antibodies from each infant with antigens from their own strains showed that not only could these antibodies discriminate among strains but antibodies in saliva samples collected at different times showed different reactivity patterns. Overall, these data suggest that, although much of the salivary SIgA antibodies reactive with A. naeslundii genospecies 1 and 2 are directed against genus-specific or more broadly cross-reactive antigens, species, genospecies, and possibly strain-specific antibodies are induced in response to colonization.

A recombinant multimeric immunoglobulin expressed in rice shows assembly-dependent subcellular localization in endosperm cells

To investigate the role of subunit assembly in the intracellular deposition of multimeric recombinant proteins, we expressed a partially humanized secretory immunoglobulin in rice endosperm cells and determined the subcellular locations of the assembled protein and its individual components. Transgenic rice plants expressing either individual subunits or all the subunits of the antibody were generated by particle bombardment, and protein localization was determined by immunoelectron microscopy. Assembly of the antibody was confirmed by immunoassay and coimmunoprecipitation. Immunolocalization experiments showed no evidence for secretion of the antibody or any of its components to the apoplast. Rather, the nonassembled light chain, heavy chain and secretory component accumulated predominantly within endoplasmic reticulum-derived protein bodies, while the assembled antibody, with antigen-binding function, accumulated specifically in protein storage vacuoles. These results show that the destination of a complex recombinant protein within the plant cell is influenced by its state of assembly.

Casein-hydrolyzing activity of sIgA antibodies from human milk

During pregnancy and immediately after delivery (i.e. at the beginning of lactation), the female organism is frequently characterized by an immune status similar to that of patients with autoimmune diseases. In addition, lactation is associated with an appearance of catalytically active antibodies or abzymes (Abzs) with DNAse, RNase, ATPase, amylolitic, protein kinase and lipid kinase activities in breast milk. However, until now there were no examples of human milk Abzs with a proteolytic activity. We present the first evidence that electrophoretically and immunologically homogeneous human milk sIgAs possess a beta-casein-hydrolyzing activity different from known proteases. Abzs specifically hydrolyze both human and bovine beta-caseins but not many other proteins tested. Using different methods including in situ analysis of proteolytic activity in a gel after SDS-PAGE it was shown that the observed proteolytic activity is an intrinsic property of human milk polyclonal sIgAs. Specific inhibitors of acidic and thiol proteases demonstrated a weak effect on proteolytic activity of Abzs, while a specific inhibitor of serine proteases (AEBSF) significantly inhibited the proteolytic activity of the abzymes. The K(M) value for human casein as a substrate was estimated (7.3 microM). Our findings suggest that the immune system of clinically healthy mothers can generate IgAs with a beta-casein-specific serine protease-like activity.

Mucosal immunology of vaccines against pathogenic nasopharyngeal bacteria

The introduction of Haemophilus influenzae type b conjugate vaccines during the 1990s was followed by dramatic decreases both in the incidence of Haemophilus influenzae type b related invasive disease and in nasopharyngeal carriage of the organism. The extent of this effect has been influenced by the fact that Haemophilus influenzae type b conjugate vaccines reduce nasopharyngeal carriage and induce herd immunity. Based on the success of Haemophilus influenzae type b conjugate vaccines, chemical conjugation has been applied to the development of pneumococcal and meningococcal polysaccharide conjugate vaccines. Evidence has begun to accumulate that these new polysaccharide based conjugate vaccines can also reduce nasopharyngeal carriage and can induce immune responses at the local mucosal level, which may be responsible for these effects. This article reviews recent studies on mucosal immune responses induced by polysaccharide based vaccines and some protein vaccine antigens against several pathogenic nasopharyngeal bacteria, and discusses the mechanisms and functions of these immune responses that may help our understanding of mucosal immune responses to both immunisation and infection.

Chlamydia pneumoniae Infection and Risk of Lung Cancer

Infection with Chlamydia pneumoniae may be associated with an increased risk of lung cancer. We conducted a matched case-control study (508 pairs) nested within a large prospective study to investigate whether IgA antibody titers to C. pneumoniae measured by the microimmunofluorescence test are associated with lung cancer risk after controlling for confounders. Individuals with antibody titers ≥16 had 1.2 times the risk of lung cancer (95% confidence interval, 0.9-1.6) compared to those with lower titers. There was a significant trend (P = 0.007) of increasing odds ratios with increasing IgA titers primarily due to an odds ratio of 2.8 (95% confidence interval, 1.1-6.7) associated with titers ≥256. Lung cancer risk associated with IgA titers ≥16 was stronger among former smokers. To better understand predictors of IgA seropositivity, we also examined demographic, lifestyle, dietary, and medical correlates of IgA titers ≥16 among controls. Those with race not classified as White or Black were more likely to have IgA titers ≥16; there were no significant differences in seropositivity by smoking behaviors. In summary, the adjusted odds ratio for lung cancer associated with IgA titers ≥16 was compatible with a weakly positive association, although nondifferential measurement error of antibody titers may have resulted in a conservative bias. Future studies using precise measures of chronic C. pneumoniae status are needed to better determine the role of this organism in the etiology of lung cancer.

Non-toxic Stx derivatives from Escherichia coli possess adjuvant activity for mucosal immunity

Both B subunit of Shiga toxin 1 (Stx1-B), which mediates the binding of toxin to the membrane, and mutant Stx1 (mStx1), which is a non-toxic double-mutated Stx1 harboring double amino acid substitutions in the A subunit, possess potent mucosal adjuvant activity. Nasal immunization of mice with ovalbumin (OVA) plus the Stx1-B or mStx1 induced OVA-specific serum IgG and mucosal IgA responses. IgG subclass analysis revealed that mStx1 and Stx1-B as mucosal adjuvants supported Ag-specific IgG1 followed by IgG2b Abs. The co-administration of either mStx1 or Stx1-B with OVA enhanced the production of IL-4, IL-5, IL-6 and IL-10 with low IFN-gamma, by OVA-specific CD4+ T cells. To better elucidate the mechanisms underlying mStx1's and Stx1-B's adjuvant activity, we next sought to examine whether or not dendritic cells (DC) residing in the nasopharyngeal-associated lymphoreticular tissue (NALT) were activated by nasal administration of Stx1-B or mStx1. We found that mice nasally administered with Stx1-B or mStx1 showed an up-regulation in the expression of CD80, CD86 and especially CD40 on NALT DCs. Taken together, these results suggest that non-toxic Stx derivatives could be effective mucosal adjuvants for the induction of Th2-type, CD4+ T cell mediated, antigen-specific mucosal IgA and systemic IgG Ab responses, and that they likely owe their adjuvant activity to the up-regulation of co-stimulatory molecules including CD80, CD86 and CD40 on NALT DCs.

Endoplasmic reticulum resident, immunoglobulin joining chain, can be secreted by perturbation of the calcium concentration in the endoplasmic reticulum

We established a transient human joining (J)-chain gene expression system in the baby hamster kidney (BHK) cell. The J-chain was detected as a 29-kDa single band on Western blotting. Immunofluorescent staining of the transfectant revealed an exclusive localization of the J-chain in the endoplasmic reticulum (ER). Intracellular transport experiment revealed that incubating conditions favorable for vesicular stomatitis virus glycoprotein (VSV-G) transport did not allow the J-chain to exit from the ER. Analysis of glycosylation status of the J-chain in the transfectant was examined by tunicamycin treatment, endoglycosidase H digestion, and also by treatment with brefeldin A. It was found that an N-glycosylation consensus site of the J-chain was functional, and intracellular J-chain was endoglycosidase H sensitive. These results indicate that, in the absence of any immunoglobulin molecules, J-chain localizes exclusively in the ER. We also tested whether the J-chain could be exported from the ER by perturbing the Ca2+ concentration in the ER. Cultivation of the J-chain transfectant in the presence of ionomycin resulted in the time-dependent secretion of the J-chain. The secreted J-chain was modified by the Golgi resident glycosylation enzymes, indicating that the secreted J-chain passed through the normal exocytic pathway.

Total viral genome copies and virus-Ig complexes after infection with influenza virus in the nasal secretions of immunized mice

The kinetics of infectious virus (p.f.u.), total virus and virus-Ig complex formation following influenza A/PR8 (H1N1) viral infection was examined in the nasal secretions of naive mice and mice immunized with A/PR8, A/Yamagata (H1N1), A/Guizhou (H3N2) and B/Ibaraki influenza viruses. The total number of virus particles and the number within virus-Ig complexes, captured in advance using an anti-mouse Ig-coated plate, were determined on the basis of viral genome copy number using quantitative RT-PCR. The kinetics of infectious and total virus particle formation, the latter of which increased by 10(3)-10(4)-fold above infectious virus numbers, showed that virus elimination from the nasal area was earlier in A/PR8, A/Yamagata and A/Guizhou-X virus-immunized mice, in decreasing order, compared with naive mice. Early virus elimination correlated with the level of A/PR8 virus-reactive antibodies in immunized mice. Virus elimination coincided with the appearance of virus-Ig complexes shortly after infection. This result suggested that antibodies led to the formation of immune complexes in a dose-dependent manner together with a reduction in number of infectious virus particles. The fact that a large number of virus particles was observed in immune complexes for a wide range antibody levels made it difficult to detect slight differences in virus number within the immune complexes, depending on antibody level. These results suggested that the formation of virus-Ig complexes in virus-immunized mice shortly after infection is involved in early virus elimination, which is determined by the strength of protective immunity against challenge viruses.