Background: Adult periodontitis (AP) is a chronic-inflammatory disease initiated by a synergistic and dysbiotic microbial community that elicits a gingival inflammatory response leading to tissue destruction. AP shares many characteristics with other chronic inflammatory diseases, including abnormal glycosylation of immunoglobulin G (IgG). Previously, we have demonstrated that IgG from gingival crevicular fluid (GCF) of patients with chronic AP contains galactose (Gal)-deficient IgG. Methods: We determined the origin of the aberrantly glycosylated IgG by measuring levels of Gal-deficient IgG in GCF and serum from AP patients and non-AP controls using lectin-ELISA. The immunoglobulin (Ig)-producing cells and the proportion of cells producing Gal-deficient IgG was immunohistochemically determined in gingival tissues from AP patients by fluorescence microscopy. The results were statistically evaluated and correlated with clinical data. Results: Our results indicate that GCF of AP patients had higher levels of Gal-deficient IgG compared to controls (P=0.002). In gingival tissues, IgG was the dominant isotype among Ig-producing cells, and 60% of IgG-positive cells produced Gal-deficient IgG. Moreover, the proportion of Gal-deficient IgG-producing cells directly correlated with clinical parameters of probing depth and clinical attachment loss. Conclusion: Our results suggest that the presence of Gal-deficient IgG is associated with gingival inflammation and may play a role in the worsening of clinical parameters of AP, such as attachment loss.
HIV-1 entry into host cells is mediated by interactions between the virus envelope glycoprotein (gp120/gp41) and host-cell receptors. N-glycans represent approximately 50% of the molecular mass of gp120 and serve as potential antigenic determinants and/or as a shield against immune recognition. We previously reported that N-glycosylation of recombinant gp120 varied, depending on the producer cells, and the glycosylation variability affected gp120 recognition by serum antibodies from persons infected with HIV-1 subtype B. However, the impact of gp120 differential glycosylation on recognition by broadly neutralizing monoclonal antibodies or by polyclonal antibodies of individuals infected with other HIV-1 subtypes is unknown.
Immunoglobulin A (IgA) nephropathy (IgAN), the leading cause of primary glomerulonephritis, is characterized by IgA1-containing immunodeposits in the glomeruli. IgAN is a chronic disease, with up to 40% of patients progressing to end-stage renal disease, with no disease-specific treatment. Multiple studies of the origin of the glomerular immunodeposits have linked elevated circulating levels of aberrantly glycosylated IgA1 (galactose-deficient in some O-glycans; Gd-IgA1) with formation of nephritogenic Gd-IgA1-containing immune complexes. Gd-IgA1 is recognized as an autoantigen in susceptible individuals by anti-glycan autoantibodies, resulting in immune complexes that may ultimately deposit in the kidney and induce glomerular injury. Genetic studies have revealed that an elevated level of Gd-IgA1 in the circulation of IgAN patients is a hereditable trait. Moreover, recent genome-wide association studies have identified several immunity-related loci that associated with IgAN. Production of Gd-IgA1 by IgA1-secreting cells of IgAN patients has been attributed to abnormal expression and activity of several key glycosyltransferases. Substantial evidence is emerging that abnormal signaling in IgA1-producing cells is related to the production of Gd-IgA1. As Gd-IgA1 is the key autoantigen in IgAN, understanding the genetic, biochemical, and environmental aspects of the abnormal signaling in IgA1-producing cells will provide insight into possible targets for future disease-specific therapy.
Although sera and all external secretions contain antibodies to human immunodeficiency virus (HIV), their levels, specificity, isotypes, and relevant effector functions display a great degree of variability. Antibodies that bind HIV antigens and neutralize the virus are predominantly associated with the IgG isotype in sera and in all external secretions, even where total levels of IgG are much lower than those of IgA. Rectal fluid that contains high IgA, but low IgG levels, displayed low neutralizing activity independent of antibodies. Therefore, external secretions should be evaluated before and after selective depletion of Ig. At the systemic level, HIV-specific IgA may interfere with the effector functions of IgG, as suggested by recent studies of individuals systemically immunized with an experimental HIV vaccine. Although HIV-specific IgG and IgA antibodies may exhibit their protective activities at mucosal surfaces through interference with viral entry and local neutralization at the systemic level, such antibodies may display discordant effector functions.
The mechanisms by which human immunodeficiency virus type 1 (HIV-1) crosses mucosal surfaces to establish infection are unknown. Acidic genital secretions of HIV-1-infected women contain HIV-1 likely coated by antibody. We found that the combination of acidic pH and Env-specific IgG, including that from cervicovaginal and seminal fluids of HIV-1-infected individuals, augmented transcytosis across epithelial cells as much as 20-fold compared with Env-specific IgG at neutral pH or non-specific IgG at either pH. Enhanced transcytosis was observed with clinical HIV-1 isolates, including transmitted/founder strains, and was eliminated in Fc neonatal receptor (FcRn)-knockdown epithelial cells. Non-neutralizing antibodies allowed similar or less transcytosis than neutralizing antibodies. However, the ratio of total:infectious virus was higher for neutralizing antibodies, indicating that they allowed transcytosis while blocking infectivity of transcytosed virus. Immunocytochemistry revealed abundant FcRn expression in columnar epithelia lining the human endocervix and penile urethra. Acidity and Env-specific IgG enhance transcytosis of virus across epithelial cells via FcRn and could facilitate translocation of virus to susceptible target cells following sexual exposure.
IgA is the most abundantly produced antibody and plays an important role in the mucosal immune system. Human IgA is represented by two isotypes, IgA1 and IgA2. The major structural difference between these two subclasses is the presence of nine potential sites of O-glycosylation in the hinge region between the first and second constant region domains of the heavy chain. Thr(225), Thr(228), Ser(230), Ser(232) and Thr(236) have been identified as the predominant sites of O-glycan attachment. The range and distribution of O-glycan chains at each site within the context of adjacent sites in this clustered region create a complex heterogeneity of surface epitopes that is incompletely defined. We previously described the analysis of IgA1 O-glycan heterogeneity by use of high resolution LC-MS and electron capture dissociation tandem MS to unambiguously localize all amino acid attachment sites in IgA1 (Ale) myeloma protein. Here, we report the identification and elucidation of IgA1 O-glycopeptide structural isomers that occur based on amino acid position of the attached glycans (positional isomers) and the structure of the O-glycan chains at individual sites (glycan isomers). These isomers are present in a model IgA1 (Mce1) myeloma protein and occur naturally in normal human serum IgA1. Variable O-glycan chains attached to Ser(230), Thr(233) or Thr(236) produce the predominant positional isomers, including O-glycans composed of a single GalNAc residue. These findings represent the first definitive identification of structural isomeric IgA1 O-glycoforms, define the single-site heterogeneity for all O-glycan sites in a single sample, and have implications for defining epitopes based on clustered O-glycan variability.
Mucosal immune system is functionally characterized by its ability to limit the access of environmental antigens such as food, airborne materials, and commensal microbes to the systemic immune compartment, leading to reduction in the magnitude of systemic immune responses. Mucosal immune system reacts at the site of antigen exposure and at anatomically distant mucosal sites by specific antibodies production and specific cellular immunity. The mucosal administration of neoantigen induces specific mucosal and systemic antibodies production and systemic effector T cells anergy accompanied by induction of regulatory T cells, phenomenon termed mucosal tolerance. Based on above observations, several studies test the ability to prevent some autoimmune diseases by mucosal administration of respective antigens but with little to no success. This review attempts to describe mechanisms involved in the induction of immune response and tolerance after immunization by mucosal routes - oral or intranasal administration. Further it aims to elucidate conditions critical for elicitation of mucosal tolerance.
Here we discuss recent advances in understanding the biochemical, immunologic, and genetic pathogenesis of IgA nephropathy, the most common primary glomerulonephritis. Current data indicate that at least four processes contribute to development of IgA nephropathy. Patients with IgA nephropathy often have a genetically determined increase in circulating levels of IgA1 with galactose-deficient O-glycans in the hinge-region (Hit 1). This glycosylation aberrancy is, however, not sufficient to induce renal injury. Synthesis and binding of antibodies directed against galactose-deficient IgA1 are required for formation of immune complexes that accumulate in the glomerular mesangium (Hits 2 and 3). These immune complexes activate mesangial cells, inducing proliferation and secretion of extracellular matrix, cytokines, and chemokines, which result in renal injury (Hit 4). Recent genome-wide association studies identify five distinct susceptibility loci--in the MHC on chromosome 6p21, the complement factor H locus on chromosome 1q32, and in a cluster of genes on chromosome 22q22--that potentially influence these processes and contain candidate mediators of disease. The significant variation in prevalence of risk alleles among different populations may also explain some of the sizable geographic variation in disease prevalence. Elucidation of the pathogenesis of IgA nephropathy provides an opportunity to develop disease-specific therapies.
IgA nephropathy (IgAN), the most common glomerulonephritis, is characterized by mesangial IgA1-containing immunodeposits, proliferation of mesangial cells, and matrix expansion. Clinical onset is frequently heralded by synpharyngitic hematuria, macroscopic hematuria during an upper-respiratory tract infection. Clinical and laboratory data support a postulated extrarenal origin of the glomerular IgA1, likely derived from circulating immune complexes containing polymeric IgA1, deficient in galactose in the hinge-region O-glycans, bound by antiglycan antibodies. This aberrant IgA1 is produced by IgA1-secreting cells with abnormal activities of specific glycosyltransferases. The galactose deficiency affects IgA1 induced by mucosal antigens and elevated circulating levels of this abnormal IgA1 are hereditable, suggesting interactions of genetic and environmental factors. An abnormal mucosal immune response resulting in production of galactose-deficient IgA1 in IgAN patients is supported by several observations: the aberrant glycosylation affects mostly polymeric IgA1 produced by mucosal-associated IgA1-secreting cells (including those from tonsils), the synpharyngitic nature of the macroscopic hematuria, and the association of disease severity with polymorphisms of a pattern-recognition receptor, TLR9. Thus, IgAN is an auto-immune disease, induced by mesangial deposition of circulating complexes containing galactose-deficient IgA1. The aberrant glycosylation of IgA1 may reflect abnormal mucosal immune responses to infections of the upper respiratory tract in genetically predisposed individuals.
Circulating immune complexes (CIC) containing galactose (Gal)-deficient IgA1 from adults with IgA nephropathy (IgAN) induce proliferation of cultured mesangial cells, but activities of CIC from pediatric patients with the disease have not been studied.
Studies of T cell-mediated immunity in the human female genital tract have been problematic due to difficulties associated with the collection of mucosal samples. Consequently, most studies rely on biopsies from the lower female genital tract or remnant tissue from hysterectomies. Availability of samples from healthy women is limited, as most studies are carried out in women with underlying pathologies. Menstruation is the cyclical sloughing off of endometrial tissue, and thus it should be a source of endometrial cells without the need for a biopsy. We isolated and phenotyped T cells from menstrual and peripheral blood and from endometrial biopsy-derived tissue from healthy women to determine the types of T cells present in this compartment. Our data demonstrated that T cells isolated from menstrual blood are a heterogeneous population of cells with markers reminiscent of blood and mucosal cells as well as unique phenotypes not represented in either compartment. T cells isolated from menstrual blood expressed increased levels of HLA-DR, ?E?7 and CXCR4 and reduced levels of CD62L relative to peripheral blood. Menstrual blood CD4+ T cells were enriched for cells expressing both CCR7 and CD45RA, markers identifying naïve T cells and were functional as determined by antigen-specific intracellular cytokine production assays. These data may open new avenues of investigation for cell mediated immune studies involving the female reproductive tract without the need for biopsies.
To address an existing controversy concerning the presence of HIV-1-specific antibodies of the IgA isotype in the female genital tract secretions of highly-exposed but persistently seronegative (HEPSN) women, 41 samples of plasma and cervicovaginal lavage (CVL) fluid were distributed to six laboratories for their blinded evaluation using ELISA with 10 different HIV-1 antigens, chemiluminescence-enhanced Western blots (ECL-WB), and virus neutralization. HIV-specific IgG or IgA antibodies in plasma samples from HEPSN women were absent or detectable only at low levels. In CVL, 11/41 samples displayed low levels of reactivity in ELISA against certain antigens. However, only one sample was positive in two of five laboratories. All but one CVL sample yielded negative results when analyzed by ECL-WB. Viral neutralizing activity was either absent or inconsistently detected in plasma and CVL. Plasma and CVL samples from 26 HIV-1-infected women were used as positive controls. Irrespective of the assays and antigens used, the results generated in all laboratories displayed remarkable concordance in the detection of HIV-1-specific antibodies of the IgG isotype. In contrast, IgA antibodies to HIV-1 antigens were not detected with consistency, and where present, IgA antibodies were at markedly lower levels than IgG. Although HIV-neutralizing activity was detected in plasma of all HIV-1-infected women, only a few of their CVL samples displayed such activity. In conclusion, frequent HIV-1 sexual exposure does not stimulate uniformly detectable mucosal or systemic HIV-1-specific responses, as convincingly documented in the present blindly performed study using a broad variety of immunological assays. Although HIV-1-infection leads to vigorous IgG responses in plasma and CVL, it does not stimulate sustained IgA responses in either fluid.
The compilation of epidemiological, virological, and immunological data clearly indicates that HIV-1 infection must be considered primarily as a disease of the mucosal immune system. The earliest and most dramatic alterations of the immune system occur in the mucosal compartment. However, the mucosal immune systems of the genital and intestinal tracts display remarkable immunological differences that must be considered in the evaluation of humoral immune responses in HIV-1-infected individuals or in volunteers immunized with experimental HIV vaccines. In this regard, marked differences in the dominant Ig isotypes, molecular forms of HIV-1-specific antibodies, and their distinct effector functions in the genital versus intestinal tracts must be carefully evaluated and considered in the measurement and interpretation of humoral immune responses. Appropriate controls and alternative immunochemical assays should be used to complement and confirm results generated by ELISA, which are prone to false positivity. Special precautions and rigorous controls must be used in the evaluation of antibody-mediated virus neutralization in external secretions of the genital and intestinal tracts.
The immune system in the gastrointestinal tract plays a crucial role in the control of infection, as it constitutes the first line of defense against mucosal pathogens. The attractive features of oral immunization have led to the exploration of a variety of oral delivery systems. However, none of these oral delivery systems have been applied to existing commercial vaccines. To overcome this, a new generation of oral vaccine delivery systems that target antigens to gut-associated lymphoid tissue is required. One promising approach is to exploit the potential of microfold (M) cells by mimicking the entry of pathogens into these cells. Targeting specific receptors on the apical surface of M cells might enhance the entry of antigens, initiating the immune response and consequently leading to protection against mucosal pathogens. In this article, we briefly review the challenges associated with current oral vaccine delivery systems and discuss strategies that might potentially target mouse and human intestinal M cells.
IgA nephropathy (IgAN) is the most common primary glomerulonephritis in the world. Aberrantly glycosylated IgA1, with galactose (Gal)-deficient hinge region (HR) O-glycans, plays a pivotal role in the pathogenesis of the disease. It is not known whether the glycosylation defect occurs randomly or preferentially at specific sites. We have described the utility of activated ion-electron capture dissociation (AI-ECD) mass spectrometric analysis of IgA1 O-glycosylation. However, locating and characterizing the entire range of O-glycan attachment sites are analytically challenging due to the clustered serine and threonine residues in the HR of IgA1 heavy chain. To address this problem, we analyzed all glycoforms of the HR glycopeptides of a Gal-deficient IgA1 myeloma protein, mimicking the aberrant IgA1 in patients with IgAN, by use of a combination of IgA-specific proteases + trypsin and AI-ECD Fourier transform ion cyclotron resonance (FT-ICR) tandem mass spectrometry (MS/MS). The IgA-specific proteases provided a variety of IgA1 HR fragments that allowed unambiguous localization of all O-glycosylation sites in the six most abundant glycoforms, including the sites deficient in Gal. Additionally, this protocol was adapted for on-line liquid chromatography (LC)-AI-ECD MS/MS and LC-electron transfer dissociation MS/MS analysis. Our results thus represent a new clinically relevant approach that requires ECD/electron transfer dissociation-type fragmentation to define the molecular events leading to pathogenesis of a chronic kidney disease. Furthermore, this work offers generally applicable principles for the analysis of clustered sites of O-glycosylation.
Aberrancies in IgA1 glycosylation have been linked to the pathogenesis of IgA nephropathy (IgAN), a kidney disease characterized by deposits of IgA1-containing immune complexes in the glomerular mesangium. IgA1 from IgAN patients is characterized by the presence of galactose (Gal)-deficient O-glycans in the hinge region that can act as epitopes for anti-glycan IgG or IgA1 antibodies. The resulting circulating immune complexes are trapped in the glomerular mesangium of the kidney where they trigger localized inflammatory responses by activating mesangial cells. Certain lectins recognize the terminal N-acetylgalactosamine (GalNAc)-containing O-glycans on Gal-deficient IgA1 and can be potentially used as diagnostic tools. To improve our understanding of GalNAc recognition by these lectins, we have conducted binding studies to assess the interaction of Helix aspersa agglutinin (HAA) and Helix pomatia agglutinin (HPA) with Gal-deficient IgA1. Surface plasmon resonance spectroscopy revealed that both HAA and HPA bind to a Gal-deficient synthetic hinge region glycopeptide (HR-GalNAc) as well as various aberrantly glycosylated IgA1 myeloma proteins. Despite having six binding sites, both HAA and HPA bind IgA1 in a functionally bivalent manner, with the apparent affinity for IgA1 related to the number of exposed GalNAc groups in the IgA1 hinge. Finally, HAA and HPA were shown to discriminate very effectively between the IgA1 secreted by cell lines derived from peripheral blood cells of patients with IgAN and that from cells of healthy controls. These studies provide insight into lectin recognition of the Gal-deficient IgA1 hinge region and lay the groundwork for the development of reliable diagnostic tools for IgAN.
The genital tract is a unique immunological environment that must support the reproductive function and resist infection. Particularly in the female tract, immunoregulatory and immunosuppressive activities that permit the growth of the fetus create an environment that can readily be exploited by microbes that have become well-adapted to this location. Cellular and molecular mediators of immune responses differ from those found at other mucosal surfaces. Mechanisms of immune response induction and delivery, as well as immune effector functions at the genital mucosae need to be considered in the development of vaccines against infections of the genital tract.
Human immunodeficiency virus type 1 (HIV-1) entry is mediated by the interaction between a variably glycosylated envelope glycoprotein (gp120) and host-cell receptors. Approximately half of the molecular mass of gp120 is contributed by N-glycans, which serve as potential epitopes and may shield gp120 from immune recognition. The role of gp120 glycans in the host immune response to HIV-1 has not been comprehensively studied at the molecular level. We developed a new approach to characterize cell-specific gp120 glycosylation, the regulation of glycosylation, and the effect of variable glycosylation on antibody reactivity. A model oligomeric gp120 was expressed in different cell types, including cell lines that represent host-infected cells or cells used to produce gp120 for vaccination purposes. N-Glycosylation of gp120 varied, depending on the cell type used for its expression and the metabolic manipulation during expression. The resultant glycosylation included changes in the ratio of high-mannose to complex N-glycans, terminal decoration, and branching. Differential glycosylation of gp120 affected envelope recognition by polyclonal antibodies from the sera of HIV-1-infected subjects. These results indicate that gp120 glycans contribute to antibody reactivity and should be considered in HIV-1 vaccine design.
Mucosal tissues of the genital tracts and the distal intestinal tract are portals of entry for infectious agents of sexually transmitted diseases, including HIV-1. Although the genital and intestinal tracts share a common embryologic origin and remain in anatomical proximity, these two sites display remarkably different immunologic features, including the levels, isotypes and molecular forms of immunoglobulins, and magnitudes and qualities of humoral and cellular immune responses. Thus, viral and bacterial infections of the genital tract or intravaginal immunizations induce, in the absence of mucosal adjuvants, minimal immune responses. Consequently, to induce relevant immune responses in the genital tract, alternative immunization routes have been explored, including systemic, intranasal, oral, or rectal immunization and their combinations. In limited studies performed in animals, systemic immunization with a subsequent mucosal (intranasal) immunization proved to be effective in the induction of humoral immune responses in genital tract secretions. The approaches have been explored to a limited extent in humans.
Although secretory IgA is the most abundantly produced Ig isotype, the mechanisms underlying the differential distribution of IgA subclasses in various body fluids remain unclear. To explore these mechanisms, we examined the distribution of IgA subclasses, the influence of the nature and sites of encounters with antigens, and the correlation between IgA subclass distribution and homing potentials of circulating IgA plasmablasts. IgA1 predominated in serum, tears, nasal wash fluid, and saliva; the levels of IgA1 and IgA2 were comparable in vaginal wash fluid; and IgA2 predominated in intestinal lavage fluids. Seventy-one percent of circulating IgA plasmablasts secreted IgA1. The intestinal homing receptor (HR), alpha4beta7, was expressed more frequently on IgA2 than on IgA1 plasmablasts, with no differences in the expression of other HRs. IgA subclass distribution among circulating antigen-specific antibody-secreting cells (ASC) was dependent on the nature of the antigen: following vaccination with Salmonella enterica serovar Typhi, unconjugated pneumococcal polysaccharide, or Haemophilus influenzae polysaccharide-diphtheria toxoid conjugate, the proportions of specific IgA1 ASC were 74%, 47%, 56%, and 80%, respectively. HR expression depended on the route of administration: expression of HRs was different after oral than after parenteral vaccination, while no difference was seen between HR expression of antigen-specific IgA1 and IgA2 ASC induced via the same route. The key factors determining IgA subclass distribution in a given secretion are the nature of the antigens encountered at a particular site and the site-specific homing instructions given to lymphocytes at that site. These two factors are reflected as differences in the homing profiles of the total populations of circulating IgA1 and IgA2 plasmablasts.
The mucosal immune system appears to be a major target of the HIV infection. Therefore, a strong pre-existing anti-HIV immune response in mucosal compartments might be able to prevent HIV infection. Conflicting views regarding the mechanisms of protection at mucosal sites, inferred by the contradictory results of mucosal vaccines in human clinical trials, attests to our lack of knowledge in understanding the human mucosal immune system. In this article, we briefly review the function of innate and adaptive immune responses and discuss current strategies and potential adjuvants in designing and delivering HIV vaccines through mucosal routes.
Worldwide, an increasing number of women use oral or injectable hormonal contraceptives. However, inadequate information is available to aid women and health care professionals in weighing the potential risks of hormonal contraceptive use in individuals living with HIV-1 or at high risk of infection. Numerous epidemiological studies and challenge studies in a rhesus macaque model suggest that progesterone-based contraceptives increase the risk of HIV-1 infection in humans and simian immunodeficiency virus (SIV) infection in macaques, accelerate disease progression, and increase viral shedding in the genital tract. However, because several other studies in humans have not observed any effect of exogenously administered progesterone on HIV-1 acquisition and disease progression, the issue continues to be a topic of intense research and ongoing discussion. In contrast to progesterone, systemic or intravaginal treatment with estrogen efficiently protects female rhesus macaques against the transmission of SIV, likely by enhancing the natural protective properties of the lower genital tract mucosal tissue. Although the molecular and cellular mechanisms underlying the effect of sex steroid hormones on HIV-1 and SIV acquisition and disease progression are not well understood, progesterone and estrogen are known to regulate a number of immune mechanisms that may exert an effect on retroviral infection. This review summarizes current knowledge of the effects of various types of sex steroid hormones on immune processes involved in the biology of HIV-1 infection.
An explanation of the principles and mechanisms involved in peaceful co-existence between animals and the huge, diverse, and ever-changing microbiota that resides on their mucosal surfaces represents a challenging puzzle that is fundamental in everyday survival. In addition to mechanical barriers and a variety of innate defense factors, mucosal immunoglobulins (Igs) provide protection by two complementary mechanisms: specific antibody activity and innate, Ig glycan-mediated binding, both of which serve to contain the mucosal microbiota in its physiological niche. Thus, the interaction of bacterial ligands with IgA glycans constitutes a discrete mechanism that is independent of antibody specificity and operates primarily in the intestinal tract. This mucosal site is by far the most heavily colonized with an enormously diverse bacterial population, as well as the most abundant production site for antibodies, predominantly of the IgA isotype, in the entire immune system. In embodying both adaptive and innate immune mechanisms within a single molecule, S-IgA maintains comprehensive protection of mucosal surfaces with economy of structure and function.
The measurement of antibodies specific for the majority of infectious agents in various external secretions is important in the evaluation of potentially protective immune responses at various sites of pathogen entry. Importantly, due to differences in the isotypes of antibodies in various body fluids, levels of total and antigen-specific antibodies in sera and secretions often display independent patterns. The measurement of mucosal antibodies to HIV presents several unique problems. Although controversial, recent results from several laboratories indicate that HIV-specific antibodies are mainly of the IgG and not IgA isotype, despite the pronounced dominance of total IgA in almost all external secretions. Due to the low levels of total IgG in such secretions, highly sensitive methods must be used, including chemiluminescence-enhanced Western blot analyses and ELISA. However, the results generated by ELISA must be interpreted with caution because of a relatively high frequency of false-positive results. Finally, due to the enormous variability of Ig levels not only in various secretions, but also in the same secretion collected at different times, determinations of total Ig levels must be performed to generate meaningful results.
The male and female genital tracts are protected by a local immune system that displays features distinguishing them from other mucosal sites. In contrast to the intestinal tract, where locally produced IgA is the dominant Ig, secretions of the male and female genital tract contain predominantly IgG of both local and systemic origin. Genital tract tissues also lack mucosal lymphoepithelial inductive sites analogous to intestinal Peyers patches; consequently, local immunization or infections with sexually transmitted pathogens induce low immune responses. Human immunodeficiency virus 1 (HIV-1) infection must be primarily considered as a mucosal disease with extensive involvement of the systemic immune compartment. Although the majority of infections is acquired through the genital mucosa, a high rate of virus replication and profound CD4(+) T cell depletion occurs in the intestinal mucosa and other mucosal tissues shortly after infection. Evaluation of HIV-specific antibodies in sera and external secretions, including vaginal washes and semen, unexpectedly revealed a selective lack of IgA responses. Moreover, specific antibody-secreting cells in peripheral blood were of the IgG isotype, even in mucosally infected individuals. Whether humoral responses to previously or newly encountered antigens are compromised in HIV-1-infected persons is under current investigation.
IgA nephropathy (IgAN) is characterized by circulating immune complexes composed of galactose-deficient IgA1 and a glycan-specific IgG antibody. These immune complexes deposit in the glomerular mesangium and induce the mesangioproliferative glomerulonephritis characteristic of IgAN. To define the precise specificities and molecular properties of the IgG antibodies, we generated EBV-immortalized IgG-secreting lymphocytes from patients with IgAN and found that the secreted IgG formed complexes with galactose-deficient IgA1 in a glycan-dependent manner. We cloned and sequenced the heavy- and light-chain antigen-binding domains of IgG specific for galactose-deficient IgA1 and identified an A to S substitution in the complementarity-determining region 3 of the variable region of the gene encoding the IgG heavy chain in IgAN patients. Furthermore, site-directed mutagenesis that reverted the residue to alanine reduced the binding of recombinant IgG to galactose-deficient IgA1. Finally, we developed a dot-blot assay for the glycan-specific IgG antibody that differentiated patients with IgAN from healthy and disease controls with 88% specificity and 95% sensitivity and found that elevated levels of this antibody in the sera of patients with IgAN correlated with proteinuria. Collectively, these findings indicate that glycan-specific antibodies are associated with the development of IgAN and may represent a disease-specific marker and potential therapeutic target.
Although human immunodeficiency virus type 1 (HIV-1)-specific antibodies are detectable in external secretions by ELISA and western blot (WB), the presence of HIV-1 neutralizing antibodies is difficult to evaluate due to the low levels of immunoglobulins (Ig) and the presence of humoral factors of innate immunity. The objective of this study was to determine virus neutralization activity and the relative contribution of HIV-1-specific antibodies of various isotypes to virus neutralization in serum/plasma samples, cervicovaginal lavages (CVL), and rectal lavages (RL).
Studies of molecular and cellular interactions involved in the pathogenesis of IgA nephropathy have revealed the autoimmune nature of this most common primary glomerulonephritis. In patients with this disease, altered glycan structures in the unique hinge region of the heavy chains of IgA1 molecules lead to the exposure of antigenic determinants, which are recognized by naturally occurring antiglycan antibodies of the IgG and/or IgA1 isotype. As a result, nephritogenic immune complexes form in the circulation and deposit in the glomerular mesangium. Deposited immune complexes induce proliferation of resident mesangial cells, increased production of extracellular matrix proteins and cytokines, and ultimately loss of glomerular function. Structural elucidation of the nature of these immune complexes and their biological activity should provide a rational basis for an effective, immunologically mediated inhibition of the formation of nephritogenic immune complexes that could be used as a disease-specific therapeutic approach.
IgA nephropathy, described in 1968 as IgA-IgG immune-complex disease, is an autoimmune disease. Galactose-deficient IgA1 is recognized by unique autoantibodies, resulting in the formation of pathogenic immune complexes that ultimately induce glomerular injury. Thus, formation of the galactose-deficient IgA1-containing immune complexes is a critical factor in the pathogenesis of IgA nephropathy. Studies of molecular defects of IgA1 can define new biomarkers specific for IgA nephropathy that can be developed into clinical assays to aid in the diagnosis, assessment of prognosis, and monitoring of disease progression.
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