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

A clinically parameterized mathematical model of Shigella immunity to inform vaccine design

We refine and clinically parameterize a mathematical model of the humoral immune response against Shigella, a diarrheal bacteria that infects 80-165 million people and kills an estimated 600,000 people worldwide each year. Using Latin hypercube sampling and Monte Carlo simulations for parameter estimation, we fit our model to human immune data from two Shigella EcSf2a-2 vaccine trials and a rechallenge study in which antibody and B-cell responses against Shigella′s lipopolysaccharide (LPS) and O-membrane proteins (OMP) were recorded. The clinically grounded model is used to mathematically investigate which key immune mechanisms and bacterial targets confer immunity against Shigella and to predict which humoral immune components should be elicited to create a protective vaccine against Shigella. The model offers insight into why the EcSf2a-2 vaccine had low efficacy and demonstrates that at a group level a humoral immune response induced by EcSf2a-2 vaccine or wild-type challenge against Shigella′s LPS or OMP does not appear sufficient for protection. That is, the model predicts an uncontrolled infection of gut epithelial cells that is present across all best-fit model parameterizations when fit to EcSf2a-2 vaccine or wild-type challenge data. Using sensitivity analysis, we explore which model parameter values must be altered to prevent the destructive epithelial invasion by Shigella bacteria and identify four key parameter groups as potential vaccine targets or immune correlates: 1) the rate that Shigella migrates into the lamina propria or epithelium, 2) the rate that memory B cells (B_M) differentiate into antibody-secreting cells (ASC), 3) the rate at which antibodies are produced by activated ASC, and 4) the Shigella-specific B_M carrying capacity. This paper underscores the need for a multifaceted approach in ongoing efforts to design an effective Shigella vaccine.

Evidence for altered levels of IgD in the nasal airway mucosa of patients with chronic rhinosinusitis

BACKGROUND

IgD is an enigmatic antibody isotype best known when coexpressed with IgM on naive B cells. However, increased soluble IgD (sIgD) levels and increased IgD+IgM- B-cell populations have been described in the human upper respiratory mucosa.

OBJECTIVE

We assessed whether levels of sIgD and IgD+ B cell counts are altered in nasal tissue from patients with chronic rhinosinusitis (CRS). We further characterized IgD+ B-cell populations and explored clinical and local inflammatory factors associated with tissue sIgD levels.

METHODS

sIgD levels were measured by means of ELISA in nasal tissues, nasal lavage fluid, sera, and supernatants of dissociated nasal tissues. IgD+ cells were identified by using immunofluorescence and flow cytometry. Inflammatory mediator levels in tissues were assessed by using real-time PCR and multiplex immunoassays. Bacterial cultures from the middle meatus were performed. Underlying medical history and medicine use were obtained from medical records.

RESULTS

sIgD levels and numbers of IgD+ cells were significantly increased in uncinate tissue (UT) of patients with chronic rhinosinusitis without nasal polyps (CRSsNP) compared with that of control subjects (4-fold, P < .05). IgD+ cells were densely scattered in the periglandular regions of UT from patients with CRSsNP. We also found that IgD+CD19+CD38bright plasmablast numbers were significantly increased in tissues from patients with CRSsNP compared with control tissues (P < .05). Among numerous factors tested, IL-2 levels were increased in UT from patients with CRSsNP and were positively correlated with tissue IgD levels. Additionally, supernatants of IL-2-stimulated dissociated tissue from patients with CRSsNP had significantly increased sIgD levels compared with those in IL-2-stimulated dissociated control tissue ex vivo (P < .05). Tissue from patients with CRS with preoperative antibiotic use or those with pathogenic bacteria showed higher IgD levels compared with tissue from patients without these variables (P < .05).

CONCLUSION

sIgD levels and IgD+CD19+CD38bright plasmablast counts were increased in nasal tissue of patients with CRSsNP. IgD levels were associated with increased IL-2 levels and the presence of pathogenic bacteria. These findings suggest that IgD might contribute to enhancement mucosal immunity or inflammation or respond to bacterial infections in patients with CRS, especially CRSsNP.

Development of a nanogel-based nasal vaccine as a novel antigen delivery system

INTRODUCTION

Nasal vaccination is one of the most effective immunization methods because it can induce effective antigen-specific immune responses not only at the mucosal site of administration but also at distant mucosal surfaces, as well as in the systemic compartment. Based on this advantage, many nasal vaccines are being developed and some have been licensed and marketed for clinical use. However, some have been withdrawn because of unacceptable adverse events such as inactivated influenza vaccine administrated with a heat-labile enterotoxin of Escherichia coli as an adjuvant. Thus, it is important to consider both the efficacy and safety of nasal vaccines. Areas covered: This review describes the benefits of cholesteryl group-bearing pullulan (CHP) nanogels for nasal vaccine delivery and vaccine development identified on Pubmed database with the term 'Nanogel-based nasal vaccine'. Expert commentary: CHP nanogels have been developed as novel drug delivery system, and a cationic CHP nanogels have been demonstrated to induce effective immunity as a nasal vaccine antigen carrier. Since vaccine antigens incorporated into CHP nanogels have exhibited no brain deposition after nasal administration in mice and nonhuman primates, the vaccine seems safe, and could be a promising new delivery system.

Continuous Dual Resetting of the Immune Repertoire as a Basic Principle of the Immune System Function

Idiopathic chronic inflammatory conditions (ICIC) such as allergy, asthma, chronic obstructive pulmonary disease, and various autoimmune conditions are a worldwide health problem. Understanding the pathogenesis of ICIC is essential for their successful therapy and prevention. However, efforts are hindered by the lack of comprehensive understanding of the human immune system function. In line with those efforts, described here is a concept of stochastic continuous dual resetting (CDR) of the immune repertoire as a basic principle that governs the function of immunity. The CDR functions as a consequence of system's thermodynamically determined intrinsic tendency to acquire new states of inner equilibrium and equilibrium against the environment. Consequently, immune repertoire undergoes continuous dual (two-way) resetting: against the physiologic continuous changes of self and against the continuously changing environment. The CDR-based dynamic concept of immunity describes mechanisms of self-regulation, tolerance, and immunosenescence, and emphasizes the significance of immune system's compartmentalization in the pathogenesis of ICIC. The CDR concept's relative simplicity and concomitantly documented congruency with empirical, clinical, and experimental data suggest it may represent a plausible theoretical framework to better understand the human immune system function.

Unbiased RACE-Based Massive Parallel Surveys of Human IgA Antibody Repertoires

For investigations of human B-cell receptor (BCR) repertoires, we have developed a protocol for large-scale surveys of human antibody heavy chain (VH) rearrangements. Here we study IgA repertoires, as more IgA antibodies are synthesized in the human body on a daily level than all other isotypes combined. In fact, IgA is secreted at all mucosal surfaces, and it is also secreted in the perspiration that coats our cutaneous surfaces. In these studies we can characterize the IgA clonal diversity of B-cell populations obtained from any donor. To recover representative repertoire libraries, we make our libraries from antibody gene transcript templates (i.e., cDNA), as these are closer reflections of the immune repertoire expressed at the antibody protein level. To avoid biases potentially introduced by upstream oligonucleotide primers that hybridize to variable region framework regions, our approach also uses rapid amplification of cDNA ends (RACE) of antibody transcripts. For exploration of human IgA responses, we have designed a duplexing antisense constant region primer that efficiently amplifies, side-by-side, heavy chain transcripts of both the IgA1 and IgA2 subclasses. By these methods we have begun to define the molecular differences in the IgA1 and IgA2 responses occurring simultaneously in different donors. These methods will be used to investigate the effects of microbial virulence factors on host defenses, during autoimmune responses, and in B-cell malignancies.

Antibodies Damage the Resilience of Fimbriae, Causing Them To Be Stiff and Tangled

As adhesion fimbriae are a major virulence factor for many pathogenic Gram-negative bacteria, they are also potential targets for antibodies. Fimbriae are commonly required for initiating the colonization that leads to disease, and their success as adhesion organelles lies in their ability to both initiate and sustain bacterial attachment to epithelial cells. The ability of fimbriae to unwind and rewind their helical filaments presumably reduces their detachment from tissue surfaces with the shear forces that accompany significant fluid flow. Therefore, the disruption of functional fimbriae by inhibiting this resilience should have high potential for use as a vaccine to prevent disease. In this study, we show that two characteristic biomechanical features of fimbrial resilience, namely, the extension force and the extension length, are significantly altered by the binding of antibodies to fimbriae. The fimbriae that were studied are normally expressed on enterotoxigenic Escherichia coli, which are a major cause of diarrheal disease. This alteration in biomechanical properties was observed with bivalent polyclonal antifimbrial antibodies that recognize major pilin subunits but not with the Fab fragments of these antibodies. Thus, we propose that the mechanism by which bound antibodies disrupt the uncoiling of natural fimbria under force is by clamping together layers of the helical filament, thereby increasing their stiffness and reducing their resilience during fluid flow. In addition, we propose that antibodies tangle fimbriae via bivalent binding, i.e., by binding to two individual fimbriae and linking them together. Use of antibodies to disrupt physical properties of fimbriae may be generally applicable to the large number of Gram-negative bacteria that rely on these surface-adhesion molecules as an essential virulence factor.

IMPORTANCE

Our study shows that the resiliency of colonization factor antigen I (CFA/I) and coli surface antigen 2 (CS2) fimbriae, which are current targets for vaccine development, can be compromised significantly in the presence of antifimbrial antibodies. It is unclear how the humoral immune system specifically interrupts infection after the attachment of enterotoxigenic Escherichia coli (ETEC) to the epithelial surface. Our study indicates that immunoglobulins, in addition to their well-documented role in adaptive immunity, can mechanically damage the resilience of fimbriae of surface-attached ETEC, thereby revealing a new mode of action. Our data suggest a mechanism whereby antibodies coat adherent and free-floating bacteria to impede fimbrial resilience. Further elucidation of this possible mechanism is likely to inform the development and refinement of preventive vaccines against ETEC diarrhea.

Toll-Like Receptor 9 Stimulation Induces Aberrant Expression of a Proliferation-Inducing Ligand by Tonsillar Germinal Center B Cells in IgA Nephropathy

The TNF family member a proliferation-inducing ligand (APRIL; also known as TNFSF13), produced by myeloid cells, participates in the generation and survival of antibody-producing plasma cells. We studied the potential role of APRIL in the pathogenesis of IgA nephropathy (IgAN). We found that a significant proportion of germinal centers (GCs) in tonsils of patients with IgAN contained cells aberrantly producing APRIL, contributing to an overall upregulation of tonsillar APRIL expression compared with that in tonsils of control patients with tonsillitis. In IgAN GC, antigen-experienced IgD^-CD38^+/-CD19⁺ B cells expressing a switched IgG/IgA B cell receptor produced APRIL. Notably, these GC B cells expressed mRNA encoding the common cleavable APRIL-α but also, the less frequent APRIL-δ/ζ mRNA, which encodes a protein that lacks a furin cleavage site and is, thus, the uncleavable membrane-bound form. Significant correlation between TLR9 and APRIL expression levels existed in tonsils from patients with IgAN. In vitro, repeated TLR9 stimulation induced APRIL expression in tonsillar B cells from control patients with tonsillitis. Clinically, aberrant APRIL expression in tonsillar GC correlated with greater proteinuria, and patients with IgAN and aberrant APRIL overexpression in tonsillar GC responded well to tonsillectomy, with parallel decreases in serum levels of galactose-deficient IgA1. Taken together, our data indicate that antibody disorders in IgAN associate with TLR9-induced aberrant expression of APRIL in tonsillar GC B cells.

Gut-lung axis: The microbial contributions and clinical implications

Gut microbiota interacts with host immune system in ways that influence the development of disease. Advances in respiratory immune system also broaden our knowledge of the interaction between host and microbiome in the lung. Increasing evidence indicated the intimate relationship between the gastrointestinal tract and respiratory tract. Exacerbations of chronic gut and lung disease have been shown to share key conceptual features with the disorder and dysregulation of the microbial ecosystem. In this review, we discuss the impact of gut and lung microbiota on disease exacerbation and progression, and the recent understanding of the immunological link between the gut and the lung, the gut-lung axis.

Immunoglobulin A nephropathy: a pathophysiology view

BACKGROUND AND AIM

IgA nephropathy is one of the leading causes of primary glomerulonephritis worldwide and an important etiology of renal disease in young adults. IgA nephropathy is considered an immune complex-mediated disease.

METHODS

This review article summarizes recent evidence on the pathophysiology of IgA nephropathy.

RESULTS

Current studies indicate an ordered sequence of multi-hits as fundamental to disease occurrence. Altered glycan structures in the hinge region of the heavy chains of IgA1 molecules act as auto-antigens, potentially triggering the production of glycan-specific autoantibodies. Recognition of novel epitopes by IgA and IgG antibodies leads to the formation of immune complexes galactose deficient-IgA1/anti-glycan IgG or IgA. Immune complexes of IgA combined with FcαRI/CD89 have also been implicated in disease exacerbation. These nephritogenic immune complexes are formed in the circulation and deposited in renal mesangium. Deposited immune complexes ultimately induce glomerular injury, through the release of pro-inflammatory cytokines, secretion of chemokines and the resultant migration of macrophages into the kidney. The TfR1/CD71 receptor has a pivotal role in mesangial cells. New signaling intracellular mechanisms have also been described.

CONCLUSION

The knowledge of the whole pathophysiology of this disease could provide the rational bases for developing novel approaches for diagnosis, for monitoring disease activity, and for disease-specific treatment.

TIR-Domain-Containing Adapter-Inducing Interferon-β (TRIF) Regulates CXCR5+ T helper Cells in the Intestine

OBJECTIVE

Establishing an effective humoral immunity is an important host defense mechanism in intestinal mucosa. T follicular helper (Tfh) cells are a spectrum of CXCR5 expressing T helper cells that induce antigen-specific B cell differentiation. Because the differentiation of T helper cells is largely regulated by innate immunity, we addressed whether TRIF signaling regulates Tfh cell differentiation and its ability to trigger humoral immune responses in the intestine.

METHOD

CD4⁺CXCR5⁺ T cells, B cells, and plasma cells in the Peyer's patches (PPs) of WT and TRIF-deficient (Trif^LPS2) mice were analyzed by flow cytometry at the baseline, 9 days post primary infection, and 7 days post-secondary infection with Y. enterocolitica. Y. enterocolitica-specific CD4⁺CXCR5⁺ T cells were generated in vitro by co-culturing peritoneal macrophages with splenic naïve T cells in the presence of Y. enterocolitica lysate. WT and Trif^LPS2 mice received CD4⁺CXCR5⁺ T cells isolated either from Y. enterocolitica-primed WT mice or generated in vitro. These mice were infected with Y. enterocolitica and followed up to 4 weeks. Y. enterocolitica-specific IgA and IgG were measured in stool and serum samples, respectively.

RESULTS

At baseline, CD4⁺CXCR5⁺ T cell proportion was higher but the proportion of B cells and plasma cells was lower in the PPs of Trif^LPS2 mice compared to WT mice. After infection, the proportion of plasma cells also became higher in the PPs of Trif^LPS2 mice compared to WT mice. Corresponding increase of Y. enterocolitica-specific stool IgA but not serum IgG was found in Trif^LPS2 mice compared to WT mice. Both in vivo isolated and in vitro generated CD4⁺CXCR5⁺ T cells induced protective immunity against Y. enterocolitica infection.

CONCLUSION

Our results reveal a novel role of TRIF in the regulation of humoral immunity in the intestine that can be utilized as a basis for a unique vaccine strategy.

A subpopulation of high IL-21-producing CD4(+) T cells in Peyer's Patches is induced by the microbiota and regulates germinal centers

The production of IL-21 by T follicular helper (Tfh) cells is vital in driving the germinal centre reaction and high affinity antibody formation. However, the degree of Tfh cell heterogeneity and function is not fully understood. We used a novel IL-21eGFP reporter mouse strain to analyze the diversity and role of Tfh cells. Through the analysis of GFP expression in lymphoid organs of IL-21eGFP mice, we identified a subpopulation of GFP⁺, high IL-21 producing Tfh cells present only in Peyer’s Patches. GFP⁺Tfh cells were found to be polyclonal and related to GFP⁻Tfh cells of Peyer’s Patches in TCR repertoire composition and overall gene expression. Studies on the mechanisms of induction of GFP⁺Tfh cells demonstrated that they required the intestinal microbiota and a diverse repertoire of CD4⁺ T cells and B cells. Importantly, ablation of GFP⁺ cells resulted in a reduced frequency of Peyer’s Patches IgG1 and germinal center B cells in addition to small but significant shifts in gut microbiome composition. Our work highlights the diversity among IL-21 producing CD4⁺ Tfh cells, and the interrelationship between the intestinal bacteria and Tfh cell responses in the gut.

Mouse and Human Liver Contain Immunoglobulin A-Secreting Cells Originating From Peyer's Patches and Directed Against Intestinal Antigens

BACKGROUND & AIMS

The liver receives blood from the gastrointestinal tract through the portal vein, and thereby is exposed continuously to dietary antigens and commensal bacteria. Alcoholic liver disease (ALD) is associated with intestinal dysbiosis, increased intestinal permeability, release of microbes into the portal circulation, and increased serum levels and liver deposits of IgA. We characterized B-cell production of IgA in livers of mice at homeostasis, after oral immunization, in a mouse model of ALD and in human liver samples.

METHODS

We performed studies with Balb/c and C57BL/6-Ly5.1 mice, as well as transgenic mice (quasimonoclonal, activation-induced [cytidine] deaminase-Cre-tamoxifen-dependent estrogen receptor 2 [ERT2], Blimp-1-green fluorescent protein [GFP]). C57BL/6-Ly5.1 mice were fed chronic plus binge ethanol to create a model of ALD. Some mice also were given repeated injections of FTY720, which prevents egress of IgA-secreting cells from Peyer's patches. We obtained nontumor liver tissues from patients with colorectal carcinoma undergoing surgery for liver metastases or hepatocellular carcinoma. B cells were isolated from mouse and human liver tissues and analyzed by flow cytometry and enzyme-linked ImmunoSpot (ELISpot). In wild-type and transgenic mice, we traced newly generated IgA-secreting cells at steady state and after oral immunization with 4-hydroxy-3-nitrophenylacetyl (NP)-Ficoll or cholera toxin. IgA responses were also evaluated in our model of ALD.

RESULTS

Livers of control mice contained proliferative plasmablasts that originated from Peyer's patches and produced IgAs reactive to commensal bacteria. After oral immunization with cholera toxin or a thymus-independent antigen, a substantial number of antigen-specific IgA-secreting cells was found in the liver. Mice fed ethanol had features of hepatitis and increased numbers of IgA-secreting cells in liver, compared with mice given control diets, as well as higher levels of serum IgA and IgA deposits in liver sinusoids. Injection of FTY720 during ethanol feeding reduced liver and serum levels of IgA and IgA deposits in liver and prevented liver injury. Human liver tissues contained a significant proportion of IgA-producing plasma cells that shared phenotypic and functional attributes with those from mouse liver, including reactivity to commensal bacteria.

CONCLUSIONS

Based on studies of mice and human liver tissues, we found the liver to be a site of IgA production by B cells, derived from gut-associated lymphoid tissues. These IgAs react with commensal bacteria and oral antigens. Livers from mice with ethanol-induced injury contain increased numbers of IgA-secreting cells and have IgA deposits in sinusoids. IgAs in the liver could mediate clearance of gut-derived antigens that arrive through portal circulation at homeostasis and protect these organs from pathogens.

Salivary IgA from the sublingual compartment as a novel noninvasive proxy for intestinal immune induction

Whole-saliva IgA appears like an attractive noninvasive readout for intestinal immune induction after enteric infection or vaccination, but has failed to show consistent correlation with established invasive markers and IgA in feces or intestinal lavage. For reference, we measured antibodies in samples from 30 healthy volunteers who were orally infected with wild-type enterotoxigenic Escherichia coli. The response against these bacteria in serum, lavage, and lymphocyte supernatants (antibody-in-lymphocyte-supernatant, ALS) was compared with that in targeted parotid and sublingual/submandibular secretions. Strong correlation occurred between IgA antibody levels against the challenge bacteria in sublingual/submandibular secretions and in lavage (r=0.69, P<0.0001) and ALS (r=0.70, P<0.0001). In sublingual/submandibular secretions, 93% responded with more than a twofold increase in IgA antibodies against the challenge strain, whereas the corresponding response in parotid secretions was only 67% (P=0.039). With >twofold ALS as a reference, the sensitivity of a >twofold response for IgA in sublingual/submandibular secretion was 96%, whereas it was only 67% in the parotid fluid. To exclude that flow rate variations influenced the results, we used albumin as a marker. Our data suggested that IgA in sublingual/submandibular secretions, rather than whole saliva with its variable content of parotid fluid, is a preferential noninvasive proxy for intestinal immune induction.

CD138 and CD31 Double-Positive Cells Comprise the Functional Antibody-Secreting Plasma Cell Compartment in Primate Bone Marrow

Plasma cells (PCs) are defined as terminally differentiated B cells that secrete large amounts of immunoglobulin (Ig). PCs that reside in the bone marrow (BM) are responsible for maintaining long-term antibody (Ab) responses after infection and vaccination, while PCs present in the blood are generally short-lived. In rhesus macaques, a species frequently used for the evaluation of human vaccines, B cells resemble those found in humans. However, a detailed characterization of BM-resident rhesus PC phenotype and function is lacking. Here, we examined Ig secretion of distinct rhesus CD138+ populations by B cell ELISpot analysis to couple phenotype with function. We demonstrate that the CD20low/-CD138+CD31+ BM population was highly enriched for antibody-secreting cells with IgG being the predominant isotype (60%), followed by IgA (33%) and IgM (7%). Transmission electron microscopy analysis confirmed PC enrichment in the CD20low/-CD138+CD31+ population with cells containing nuclei with "spokes of a wheel" chromatin structure and prominent rough endoplasmic reticulum. This panel also stained human BM PCs and allowed a clear distinction between BM PCs and short-lived peripheral PCs, providing an improved strategy to isolate PCs from rhesus BM for further analysis.

The Distribution of SIgA and IgG Antibody-Secreting Cells in the Small Intestine of Bactrian Camels (Camelus bactrianus) of Different Ages

Secretory immunoglobulin A (SIgA) and immunoglobulin G (IgG) antibody-secreting cells (ASCs) are two important cell types in the mucosal immune system. This study aimed to explore the distribution of these ASC populations in the small intestine of Bactrian camels of different ages. Twenty-four Alashan Bactrian camels were divided into the following four age groups: young (1–2 years), pubertal (3–5 years), middle-aged (6–16 years) and old (17–20 years). SIgA and IgG ASCs in the intestinal mucosa lamina propria (LP) were observed and analyzed using immunohistochemcal techniques. The results from all age groups show that both SIgA and IgG ASCs were diffusely distributed in the intestinal LP, and some cells aggregated around the crypts. Moreover, the densities of the two ASC populations gradually increased from the duodenum to the jejunum and then decreased in the ileum. Meanwhile, there were more SIgA ASCs than IgG ASCs in the duodenum, jejunum, and ileum, and these differences were significant in the young and pubertal groups (P<0.05). In addition, the SIgA and IgG ASC densities increased from the young to the pubertal period, peaked at puberty, and then gradually decreased with age. The results demonstrate that the SIgA and IgG ASC distributions help to form two immunoglobulin barriers in the intestinal mucosa to provide full protection, helping to maintain homeostasis. These findings also underscore the importance of researching the development and degeneration of intestinal mucosal immunity in Bactrian camels.

Nutritional immunology: function of natural killer cells and their modulation by resveratrol for cancer prevention and treatment

Natural killer (NK) cells as part of the innate immune system represent the first line of defence against (virus-) infected and malignantly transformed cells. The emerging field of nutritional immunology focuses on compounds featuring immune-modulating activities in particular on NK cells, which e.g. can be exploited for cancer prevention and treatment. The plant-based nutrition resveratrol is a ternary hydroxylated stilbene, which is present in many foods and beverages, respectively. In humans it comprises a large variety of distinct biological activities. Interestingly, resveratrol strongly modulates the immune response including the activity of NK cells. This review will give an overview on NK cell functions and summarize the resveratrol-mediated modulation thereof.

Circulating memory B cells and plasmablasts are associated with the levels of serum immunoglobulin in patients with ulcerative colitis

Humoural immunity is crucial for the pathogenesis of ulcerative colitis (UC), but the precise perturbation of B cell immunity is poorly understood. This study is aimed at evaluating the numbers of different subsets of circulating memory B cells, plasmablasts, and the levels of serum immunoglobulin in UC patients. Total of 23 patients with active UC and 14 healthy controls (HC) were examined for the numbers of different subsets of circulating memory B cells and plasmablasts before and after treatment with mesalazine for 8-12 weeks by flow cytometry. Disease activity was evaluated by the Mayo clinic score. The levels of serum immunoglobulin, C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) were measured in individual subjects. In comparison with that in HC, significantly reduced numbers of IgG(+) IgD(-) CD27(+) CD19(+) memory B cells, increased numbers of CD20(-) CD19(+) plasmablast subsets, and higher serum IgG levels were detected in UC patients. The concentrations of serum IgG, the numbers of CD138(+) CD38(+) CD20(-) CD19(+), and IgG(+) CD38(+) CD20(-) CD19(+) plasmablasts were negatively associated with the numbers of IgG(+) IgD(-) CD27(+) CD19(+) memory B cells. Furthermore, the values of Mayo clinic score, CRP, or ESR in UC patients were negatively correlated with the numbers of IgG(+) IgD(-) CD27(+) CD19(+) memory B cells, while positively correlated with the serum IgG levels and the numbers of plasmablast subsets. Following treatment with mesalazine, the numbers of circulating IgG(+) IgD(-) CD27(+) CD19(+) memory B cells were significantly increased, while the numbers of CD138(+) CD38(+) CD20(-) CD19(+) and IgG(+) CD38(+) CD20(-) CD19(+) plasmablasts were reduced in UC patients. These decreased IgG(+) IgD(-) CD27(+) CD19(+) memory B cells and increased plasmablasts may be involved in the pathogenic process of UC.

Immune Defense in Upper Airways: A Single-Cell Study of Pathogen-Specific Plasmablasts and Their Migratory Potentials in Acute Sinusitis and Tonsillitis

Background

Despite the high frequency of upper respiratory tract (URT) infections and use of the nasal mucosa as route for vaccination, the local immune mechanism and dissemination of effector lymphocytes from the URT have been insufficiently characterized. To devise a single-cell approach for studying the mucosal immune response in the URT, we explored URT-originating B effector lymphocytes in the circulation of patients with one of two common respiratory infections, acute sinusitis or tonsillitis.

Methods

Patients with acute sinusitis (n = 13) or tonsillitis (n = 11) were investigated by ELISPOT for circulating pathogen-specific antibody-secreting cells (ASCs) of IgA, IgG and IgM isotypes approximately one week after the onset of symptoms. These cells’ potential to home into tissues was explored by assessing their expression of tissue-specific homing receptors α₄β₇, L-selectin, and cutaneous lymphocyte antigen (CLA).

Results

Pathogen-specific ASCs were detected in the circulation of all patients, with a geometric mean of 115 (95% CI 46–282) /10⁶ PBMC in sinusitis, and 48 (27–88) in tonsillitis. These responses were mainly dominated by IgG. In sinusitis α₄β₇ integrin was expressed by 24% of the ASCs, L-selectin by 82%, and CLA by 21%. The proportions for tonsillitis were 15%, 80%, and 23%, respectively. Healthy individuals had no ASCs.

Conclusions

URT infections–acute sinusitis and tonsillitis–both elicited a response of circulating pathogen-specific plasmablasts. The magnitude of the response was greater in sinusitis than tonsillitis, but the homing receptor profiles were similar. Human nasopharynx-associated lymphoid structures were found to disseminate immune effector cells with a distinct homing profile.

Alginic acid oligosaccharide accelerates weaned pig growth through regulating antioxidant capacity, immunity and intestinal development

Alginic acid oligosaccharide (ALGO) is the lyase–lysate of alginic acid, which is a naturally occurring anionic polysaccharide isolated from the cell walls of seaweed.

Fecal antibody levels as a noninvasive method for measuring immunity to gastrointestinal nematodes in ecological studies

Among‐individual variation in antibody‐associated immunity to gastrointestinal nematode parasites (GIN) is known be associated with life‐history traits and vital rates in wild vertebrate systems. To date, measurement of levels of antibodies against GIN antigens in natural populations has exclusively been based on invasive blood sampling techniques. Previous work in laboratory rodents and ruminant livestock suggests that antibody measures from feces may provide a viable noninvasive approach. We measured total and anti‐GIN antibodies of different isotypes (immunoglobulin (Ig) G, IgA and IgE) from paired samples of plasma and feces from free‐living Soay sheep of different ages and sexes. We tested the correlations among these measures as well as their associations with body mass and Strongyle nematode fecal egg counts (FEC). Significant positive correlations were present among plasma and fecal anti‐GIN antibody levels for IgG and IgA. Generally, correlations between total antibody levels in plasma and feces were weaker and not significant. No significant relationships were found between any antibody measures and body mass; however, fecal anti‐GIN antibody levels were significantly negatively correlated with FEC. Our data clearly demonstrate the feasibility of measuring anti‐GIN antibodies from fecal samples collected in natural populations. Although associations of fecal antibody levels with their plasma counterparts and FEC were relatively weak, the presence of significant correlations in the predicted direction in a relatively small and heterogeneous sample suggests fecal antibody measures could be a useful, noninvasive addition to current eco‐immunological studies.

Tracheal and bronchial polymeric immunoglobulin secretory immune system (PISIS) development in a porcine model

Polymeric immunoglobulins (pIgs) mucosal secretion is mediated by the pIg secretory immune system (PISIS), which is composed of J-chain (JC) and antibody (IgM/IgA) producing cells (JC-AbPC), pIg receptor (pIgR) epithelial cell expression and the efficient release of secretory Igs (SIgs) to the mucosal lumen. A poor development or disturbances in this system may cause higher infection susceptibility, as observed in young and elderly people. In spite of this system's importance, few detailed studies regarding its development have been described in the lower respiratory tract of humans. Because the porcine model has been reported as an option for translational medicine to humans, we studied the tracheal and bronchial PISIS development in healthy, non-vaccinated, SPF, miniature Vietnamese pigs from birth to adulthood using immunohistochemistry and ELISAs. Our results demonstrated that pIgR was present at birth, and its expression increased with age. In contrast, JC-AbPC were low in neonatal pigs; however, colostrum was a source of IgM, SIgA, total IgA and IgG in respiratory secretions (trachea and bronchoalveolar lavages, nasal secretion and saliva) in piglets. JC-AbPC steadily increased in post-weaned, young and adult pigs, correlating with considerable increases in secretory and total Igs in the trachea and bronchi. These data suggest a compensatory role of maternal Igs at the respiratory mucosa in the absence of a structured PISIS before weaning. Furthermore, monomeric Igs (IgG and IgA) may also play an important role in respiratory protection and deserves a more thorough study.

Plasmacytoid dendritic cells are dispensable for noninfectious intestinal IgA responses in vivo

Intestinal DCs orchestrate gut immune homeostasis by dampening proinflammatory T-cell responses and inducing anti-inflammatory IgA responses. Although no specific DC subset has been strictly assigned so far to govern IgA response, some candidate subsets emerge. In particular, plasmacytoid DCs (pDCs), which notoriously promote anti-viral immunity and T-cell tolerance to innocuous antigens (Ags), contribute to IgA induction in response to intestinal viral infection and promote T-cell-independent IgA responses in vitro. Here, using two transgenic mouse models, we show that neither short-term nor long-term pDC depletion alters IgA class switch recombination in Peyer's patches and frequency of IgA plasma cells in intestinal mucosa at steady state, even in the absence of T-cell help. In addition, pDCs are dispensable for induction of intestinal IgA plasma cells in response to oral immunization with T-cell-dependent or T-cell-independent Ags, and are not required for proliferation and IgA switch of Ag-specific B cells in GALT. These results show that pDCs are dispensable for noninfectious IgA responses, and suggest that various DC subsets may play redundant roles in the control of intestinal IgA responses.

Secretory IgA from submucosal glands does not compensate for its airway surface deficiency in chronic obstructive pulmonary disease

Secretory immunoglobulin A (SIgA) reaches the airway lumen by local transcytosis across airway epithelial cells or with tracheobronchial submucosal gland secretions. In chronic obstructive pulmonary disease (COPD), deficiency of SIgA on the airway surface has been reported. However, reduction of SIgA levels in sputum and bronchoalveolar lavage (BAL) fluid has not been consistently observed. To explain this discrepancy, we analyzed BAL fluid and lung tissue from patients with COPD and control subjects. Immunohistochemical analysis of large and small airways of COPD patients showed that MUC5AC is the predominant mucin expressed by airway epithelial cells, whereas MUC5B is expressed in submucosal glands of large airways. Dual immunostaining with anti-IgA and anti-MUC5B antibodies showed reduction of IgA on the airway surface as well as accumulation of IgA within MUC5B-positive luminal mucus plugs, suggesting that luminal SIgA originates from submucosal glands in COPD patients. We found that the concentration of SIgA in BAL is inversely correlated with forced expiratory volume in 1 s (FEV₁) in COPD, but that the ratio of SIgA/MUC5B is a better predictor of FEV₁, particularly in patients with moderate COPD. Together, these findings suggest that SIgA production by submucosal glands, which are expanded in COPD, is insufficient to compensate for reduced SIgA transcytosis by airway epithelial cells. Localized SIgA deficiency on the surface of small airways is associated with COPD progression and represents a potential new therapeutic target in COPD.

Host entry by gamma-herpesviruses--lessons from animal viruses?

The oncogenicity of gamma-herpesviruses (γHVs) motivates efforts to control them and their persistence makes early events key targets for intervention. Human γHVs are often assumed to enter naive hosts orally and infect B cells directly. However, neither assumption is supported by direct evidence, and vaccination with the Epstein-Barr virus (EBV) gp350, to block virion binding to B cells, failed to reduce infection rates. Thus, there is a need to re-evaluate assumptions about γHV host entry. Given the difficulty of analysing early human infections, potentially much can be learned from animal models. Genomic comparisons argue that γHVs colonized mammals long before humans speciation, and so that human γHVs are unlikely to differ dramatically in behaviour from those of other mammals. Murid Herpesvirus-4 (MuHV-4), which like EBV and the Kaposi's Sarcoma-associated Herpesvirus (KSHV) persists in memory B cells, enters new hosts via olfactory neurons and exploits myeloid cells to spread. Integrating these data with existing knowledge of human and veterinary γHVs suggests a new model of host entry, with potentially important implications for infection control.

Immunoglobulin A in serum: an old acquaintance as a new prognostic biomarker in idiopathic pulmonary fibrosis

Immunoglobulin (Ig)A is an important immunoglobulin in mucosal immunity and protects the lungs against invading pathogens. The production of IgA is regulated by transforming growth factor (TGF)-β, a versatile cytokine and key player in the pathogenesis of pulmonary fibrosis. TGF-β is up-regulated in patients with idiopathic pulmonary fibrosis (IPF), but difficult to use as a biomarker. The aim of this study was to evaluate the prognostic value of IgA in serum in patients with IPF. We examined IgA levels at time of diagnosis in 86 patients diagnosed with IPF. Mean serum IgA level in IPF is 3·22 g/l and regression analyses showed a significant association with mortality (hazard ratio = 1·445, P = 0·002). A significantly worse survival was found in patients with IgA serum levels > 2·85 g/l compared to patients with lower IgA serum levels (P = 0·003). These findings were confirmed in a duplication cohort. In conclusion, the level of IgA in blood is a promising prognostic marker in IPF and can be implemented easily in the hospital setting. Future studies are warranted to investigate if repeated measurements of serum IgA can further improve the performance of serum IgA as a prognostic marker.

Phenotypic Analysis of a Population of IgA+ Cells in the Follicle-Associated Epithelium of Mouse Peyer's Patches

The follicle-associated epithelium (FAE) selectively transports prions, viruses, pathogenic bacteria, commensal microflora, and even secretory IgA (SIgA)-immune complexes from the intestinal lumen to underlying gut-associated lymphoid tissues like Peyer’s patches. The FAE consists of a single layer of columnar epithelial cells that includes enterocytes and M (microfold) cells, intermingled with dendritic cells (DCs), macrophages, and naïve and memory B and T lymphocytes. In this report we describe a population of IgA⁺ cells that reside within and immediately below the FAE in mouse Peyer’s patches. Immunofluorescence microscopy analysis indicated that the FAE-associated IgA⁺ cells were negative for surface antigen markers specific for B cells (B220), T cells (CD3), DCs (CD11c), and plasma cells (CD138). The IgA⁺ cells were also negative Ki-67 and IRF4, indicating that they are not mature B cells or plasma cells. The IgA⁺ cells were, however, often found in close proximity to DCs, leading us to speculate that the population of IgA⁺ cells in the FAE constitutes an atypical subset of B cells involved in mucosal antigen surveillance and/or immune recall.

Differences in Homing Potentials of Streptococcus pneumoniae-Specific Plasmablasts in Pneumococcal Pneumonia and After Pneumococcal Polysaccharide and Pneumococcal Conjugate Vaccinations

Background. Mucosal immune mechanisms in the upper and lower respiratory tracts may serve a critical role in preventing pneumonia due to Streptococcus pneumoniae. Streptococcus pneumoniae–specific plasmablasts presumably originating in the lower respiratory tract have recently been found in the circulation in patients with pneumonia. The localization of an immune response can be evaluated by exploring homing receptors on such plasmablasts, yet no data have thus far described homing receptors in pneumonia.

Methods. The expression of α₄β₇, L-selectin, and cutaneous lymphocyte antigen (CLA) on S. pneumoniae–specific plasmablasts was examined in patients with pneumonia (n = 16) and healthy volunteers given pneumococcal polysaccharide vaccine (PPV; n = 14) or pneumococcal conjugate vaccine (PCV; n = 11).

Results. In patients with pneumonia, the proportion of S. pneumoniae–specific plasmablasts expressing L-selectin was high, the proportion expressing α₄β₇ was moderate, and the proportion expressing CLA was low. The homing receptor α₄β₇ was expressed more frequently in the pneumonia group than in the PPV (P = .000) and PCV (P = .029) groups, L-selectin was expressed more frequently in the PPV group than in the PCV group (P = .014); and CLA was expressed more frequently in the pneumonia group than in the PPV group (P = .001).

Conclusions. The homing receptor profile in patients with pneumonia was unique yet it was closer to that in PCV recipients than in PPV recipients. These data suggest greater mucosal localization for immune response in natural infection, which is clinically interesting, especially considering the shortcomings of vaccines in protecting against noninvasive pneumonia.

Putting J chain back on the map: how might its expression define plasma cell development?

Joining chain (J chain) is a small polypeptide that regulates multimerization of secretory IgM and IgA, the only two mammalian Igs capable of forming multimers. J chain also is required for poly-Ig receptor-mediated transport of these Ig classes across the mucosal epithelium. It is generally assumed that all plasma cells express J chain regardless of expressed isotype, despite the documented presence of J chain(-) plasma cells in mammals, specifically in all monomeric IgA-secreting cells and some IgG-secreting cells. Compared with most other immune molecules, J chain has not been studied extensively, in part because of technical limitations. Even the reported phenotype of the J chain-knockout mouse is often misunderstood or underappreciated. In this short review, we discuss J chain in light of the various proposed models of its expression and regulation, with an added focus on its evolutionary significance, as well as its expression in different B cell lineages/differentiation states.

Re-thinking the functions of IgA(+) plasma cells

The intestinal mucosa harbors the largest population of antibody (Ab)-secreting plasma cells (PC) in the human body, producing daily several grams of immunoglobulin A (IgA). IgA has many functions, serving as a first-line barrier that protects the mucosal epithelium from pathogens, toxins and food antigens (Ag), shaping the intestinal microbiota, and regulating host-commensal homeostasis. Signals induced by commensal colonization are central for regulating IgA induction, maintenance, positioning and function and the number of IgA(+) PC is dramatically reduced in neonates and germ-free (GF) animals. Recent evidence demonstrates that the innate immune effector molecules tumor necrosis factor α (TNFα) and inducible nitric oxide synthase (iNOS) are required for IgA(+) PC homeostasis during the steady state and infection. Moreover, new functions ascribed to PC independent of Ab secretion continue to emerge, suggesting that PC, including IgA(+) PC, should be re-examined in the context of inflammation and infection. Here, we outline mechanisms of IgA(+) PC generation and survival, reviewing their functions in health and disease.

Nasal immunity is an ancient arm of the mucosal immune system of vertebrates

The mucosal surfaces of all vertebrates have been exposed to similar evolutionary pressures for millions of years. In terrestrial vertebrates such as birds and mammals, the nasopharynx-associated lymphoid tissue (NALT) represents a first line of immune defence. Here we propose that NALT is an ancient arm of the mucosal immune system not restricted to terrestrial vertebrates. We find that NALT is present in rainbow trout and that it resembles other teleost mucosa-associated lymphoid tissues. Trout NALT consists of diffuse lymphoid cells and lacks tonsils and adenoids. The predominant B-cell subset found in trout NALT are IgT(+) B cells, similar to skin and gut. The trout olfactory organ is colonized by abundant symbiotic bacteria, which are coated by trout secretory immunoglobulin. Trout NALT is capable of mounting strong anti-viral immune responses following nasal delivery of a live attenuated viral vaccine. Our results open up a new tool for the control of aquatic infectious diseases via nasal vaccination.

C-type lectin-like receptor LOX-1 promotes dendritic cell-mediated class-switched B cell responses

Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) is a pattern-recognition receptor for a variety of endogenous and exogenous ligands. However, LOX-1 function in the host immune response is not fully understood. Here, we report that LOX-1 expressed on dendritic cells (DCs) and B cells promotes humoral responses. On B cells LOX-1 signaling upregulated CCR7, promoting cellular migration toward lymphoid tissues. LOX-1 signaling on DCs licensed the cells to promote B cell differentiation into class-switched plasmablasts and led to downregulation of chemokine receptor CXCR5 and upregulation of chemokine receptor CCR10 on plasmablasts, enabling their exit from germinal centers and migration toward local mucosa and skin. Finally, we found that targeting influenza hemagglutinin 1 (HA1) subunit to LOX-1 elicited HA1-specific protective antibody responses in rhesus macaques. Thus, LOX-1 expressed on B cells and DC cells has complementary functions to promote humoral immune responses.

Regional specialization within the intestinal immune system

The intestine represents the largest compartment of the immune system. It is continually exposed to antigens and immunomodulatory agents from the diet and the commensal microbiota, and it is the port of entry for many clinically important pathogens. Intestinal immune processes are also increasingly implicated in controlling disease development elsewhere in the body. In this Review, we detail the anatomical and physiological distinctions that are observed in the small and large intestines, and we suggest how these may account for the diversity in the immune apparatus that is seen throughout the intestine. We describe how the distribution of innate, adaptive and innate-like immune cells varies in different segments of the intestine and discuss the environmental factors that may influence this. Finally, we consider the implications of regional immune specialization for inflammatory disease in the intestine.

A single, low dose oral antigen exposure in newborn piglets primes mucosal immunity if administered with CpG oligodeoxynucleotides and polyphosphazene adjuvants

By definition, soluble antigens ingested orally trigger mucosal tolerance such that any subsequent re-exposure by a systemic route results in suppression of immunity. We propose that antigens introduced in extreme early life can readily traverse the gut wall and therefore circumvent induction of mucosal tolerance and instead induce immunity. Piglets were drenched with low-doses of ovalbumin (OVA; 5mg or 0.05 mg) alone, OVA plus adjuvants (CpG oligodeoxynucleotides and PCEP polyphosphazene) or saline within 6h of birth. At 28 days of age, they were administered 10mg OVA plus 1:1 Montanide adjuvant (or saline) via the intraperitoneal (i.p.) route or via the oral route. Serum was obtained on day 28 and day 49 to measure OVA-specific antibodies titres. All piglets boosted orally with OVA plus Montanide, regardless of prior OVA exposure, failed to induce immunity. As expected, piglets drenched with saline but boosted via the i.p. route with OVA plus Montanide showed significant induction of anti-OVA IgA, IgG, IgG1 and IgG2 relative to saline control piglets. Newborn animals drenched with 5mg or 0.05 mg OVA failed to induce oral immunity. A second intramuscular injection in adulthood triggered immunity in the piglets that were drenched with 0.05 mg OVA and boosted initially by the i.p. route suggesting that some systemic lymphocytes were primed despite initial lack of induction of humoral immunity. In contrast, piglets orally immunized with 5mg or 0.05 mg OVA plus adjuvants resulted in significant induction of anti-OVA IgA (5mg only), IgM, IgG, IgG1 and IgG2 in serum relative to saline control piglets as well as significant induction of anti-OVA IgA, IgM (5mg only) IgG, IgG1 (5mg only) or IgG2 relative to piglets drenched with OVA alone. These data clearly show that the response was sensitive to the oral vaccine components and was not simply a response to the i.p. immunization at day 28. This work demonstrates that newborn piglets respond to oral antigens with immunity if re-exposure to the antigen occurs via a systemic route and if adjuvants are included with the oral vaccine administered at birth. These results should be further explored to establish whether early life oral vaccination can be exploited to protect this susceptible population against infectious diseases.

Which Antibody Functions are Important for an HIV Vaccine?

HIV antibody (Ab) functions capable of preventing mucosal cell-free or cell-to-cell HIV transmission are critical for the development of effective prophylactic and therapeutic vaccines. In addition to CD4(+) T cells, other potential HIV-target cell types including antigen-presenting cells (APCs) (dendritic cells, macrophages) residing at mucosal sites are infected. Moreover, the interactions between APCs and HIV lead to HIV cell-to-cell transmission. Recently discovered broadly neutralizing antibodies (NAbs) are able to neutralize a broad spectrum of HIV strains, inhibit cell-to-cell transfer, and efficiently protect from infection in the experimentally challenged macaque model. However, the 31% protection observed in the RV144 vaccine trial in the absence of detectable NAbs in blood samples pointed to the possible role of additional Ab inhibitory functions. Increasing evidence suggests that IgG Fcγ receptor (FcγR)-mediated inhibition of Abs present at the mucosal site may play a role in protection against HIV mucosal transmission. Moreover, mucosal IgA Abs may be determinant in protection against HIV sexual transmission. Therefore, defining Ab inhibitory functions that could lead to protection is critical for further HIV vaccine design. Here, we review different inhibitory properties of HIV-specific Abs and discuss their potential role in protection against HIV sexual transmission.

Plasma cells in the mucosa of patients with inflammatory bowel disease produce granzyme B and possess cytotoxic activities

In both Crohn's disease (CD) and ulcerative colitis (UC), the gut is massively infiltrated with B cells and plasma cells, but the role of these cell types in the pathogenesis of gut tissue damage remains largely unknown. Human B cells express granzyme B (GrB) when cultured with IL-21, a cytokine overproduced in CD and UC mucosa. We therefore examined whether mucosal B cells express GrB and have cytotoxic activity in inflammatory bowel disease (IBD). GrB-expressing CD19(+) and IgA(+) cells were seen in the normal intestinal mucosa, but they were significantly more frequent in both CD and UC. In contrast, only a minority of CD19(+) and IgA(+) cells expressed perforin with no difference between IBD and controls. GrB-producing CD19(+) cells expressed CD27 and were CD38(high) and CD20 negative. CD19(+) B cells from IBD patients induced HCT-116 cell death. IL-21 enhanced GrB expression in control CD19(+) B cells and increased their cytotoxic activity. These data indicate that IBD-related inflammation is marked by mucosal accumulation of cytotoxic, GrB-expressing CD19(+) and IgA(+) cells, suggesting a role for these cells in IBD-associated epithelial damage.

Phenotypes and distribution of mucosal memory B-cell populations in the SIV/SHIV rhesus macaque model

As vaccine-elicited antibodies have now been associated with HIV protective efficacy, a thorough understanding of mucosal and systemic B-cell development and maturation is needed. We phenotyped mucosal memory B-cells, investigated isotype expression and homing patterns, and defined plasmablasts and plasma cells at three mucosal sites (duodenum, jejunum and rectum) in rhesus macaques, the commonly used animal model for pre-clinical vaccine studies. Unlike humans, macaque mucosal memory B-cells lacked CD27 expression; only two sub-populations were present: naïve (CD21(+)CD27(-)) and tissue-like (CD21(-)CD27(-)) memory. Similar to humans, IgA was the dominant isotype expressed. The homing markers CXCR4, CCR6, CCR9 and α4β7 were differentially expressed between naïve and tissue-like memory B-cells. Mucosal plasmablasts were identified as CD19(+)CD20(+/-)HLA-DR(+)Ki-67(+)IRF4(+)CD138(+/-) and mucosal plasma cells as CD19(+)CD20(-)HLA-DR(-)Ki-67(-)IRF4(+)CD138(+). Both populations were CD39(+/-)CD27(-). Plasma cell phenotype was confirmed by spontaneous IgA secretion by ELISpot of positively-selected cells and J-chain expression by real-time PCR. Duodenal, jejunal and rectal samples were similar in B-cell memory phenotype, isotype expression, homing receptors and plasmablast/plasma cell distribution among the three tissues. Thus rectal biopsies adequately monitor B-cell dynamics in the gut mucosa, and provide a critical view of mucosal B-cell events associated with development of vaccine-elicited protective immune responses and SIV/SHIV pathogenesis and disease control.

Effect of age and maternal antibodies on the systemic and mucosal immune response after neonatal immunization in a porcine model

Newborn mammals are highly susceptible to respiratory infections. Although maternal antibodies (MatAb) offer them some protection, they may also interfere with their systemic immune response to vaccination. However, the impact of MatAb on the neonatal mucosal immune response remains incompletely described. This study was performed to determine the effect of ovalbumin (OVA) -specific MatAb on the anti- OVA antibody response in sera, nasal secretions and saliva from specific pathogen-free Vietnamese miniature piglets immunized at 7 or 14 days of age. Our results demonstrated that MatAb increased antigen-specific IgA and IgG responses in sera, and transiently enhanced an early secretory IgA response in nasal secretions of piglets immunized at 7 days of age. In contrast, we detected a lower mucosal (nasal secretion and saliva) anti- OVA IgG response in piglets with MatAb immunized at 14 days of age, compared with piglets with no MatAb, suggesting a modulatory effect of antigen-specific maternal factors on the isotype transfer to the mucosal immune exclusion system. In our porcine model, we demonstrated that passive maternal immunity positively modulated the systemic and nasal immune responses of animals immunized early in life. Our results, therefore, open the possibility of inducing systemic and respiratory mucosal immunity in the presence of MatAb through early vaccination.