Origin of galactose-deficient immunoglobulin g in gingival crevicular fluid in periodontitis

BACKGROUND

Periodontitis is a chronic inflammatory disease initiated by a synergistic and dysbiotic microbial community that elicits a gingival inflammatory response leading to tissue breakdown. Periodontitis shares many characteristics with other chronic inflammatory diseases, including abnormal glycosylation of immunoglobulin (Ig)G. The current authors have previously demonstrated that IgG from gingival crevicular fluid (GCF) of patients with chronic periodontitis contains galactose (Gal)-deficient IgG.

METHODS

The origin of the aberrantly glycosylated IgG was determined by measuring levels of Gal-deficient IgG in GCF and serum from patients with periodontitis and non-periodontitis controls using lectin enzyme-linked immunosorbent assay. The Ig-producing cells and the proportion of cells producing Gal-deficient IgG were immunohistochemically determined in gingival tissues from patients with periodontitis by fluorescence microscopy. The results were statistically evaluated and correlated with clinical data.

RESULTS

The results indicate that GCF of patients with periodontitis had higher levels of Gal-deficient IgG compared with 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 (AL).

CONCLUSION

These 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 periodontitis, such as AL.

Differential glycosylation of envelope gp120 is associated with differential recognition of HIV-1 by virus-specific antibodies and cell infection

BACKGROUND

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.

METHODS

Recombinant multimerizing gp120 antigens were expressed in different cells, HEK 293T, T-cell, rhabdomyosarcoma, hepatocellular carcinoma, and Chinese hamster ovary cell lines. Binding of broadly neutralizing monoclonal antibodies and polyclonal antibodies from sera of subtype A/C HIV-1-infected subjects with individual gp120 glycoforms was assessed by ELISA. In addition, immunodetection was performed using Western and dot blot assays. Recombinant gp120 glycoforms were tested for inhibition of infection of reporter cells by SF162 and YU.2 Env-pseudotyped R5 viruses.

RESULTS

We demonstrated, using ELISA, that gp120 glycans sterically adjacent to the V3 loop only moderately contribute to differential recognition of a short apex motif GPGRA and GPGR by monoclonal antibodies F425 B4e8 and 447-52D, respectively. The binding of antibodies recognizing longer peptide motifs overlapping with GPGR epitope (268 D4, 257 D4, 19b) was significantly altered. Recognition of gp120 glycoforms by monoclonal antibodies specific for other than V3-loop epitopes was significantly affected by cell types used for gp120 expression. These epitopes included CD4-binding site (VRC03, VRC01, b12), discontinuous epitope involving V1/V2 loop with the associated glycans (PG9, PG16), and an epitope including V3-base-, N332 oligomannose-, and surrounding glycans-containing epitope (PGT 121). Moreover, the different gp120 glycoforms variably inhibited HIV-1 infection of reporter cells.

CONCLUSION

Our data support the hypothesis that the glycosylation machinery of different cells shapes gp120 glycosylation and, consequently, impacts envelope recognition by specific antibodies as well as the interaction of HIV-1 gp120 with cellular receptors. These findings underscore the importance of selection of appropriately glycosylated HIV-1 envelope as a vaccine antigen.

Humoral immune responses to HIV in the mucosal secretions and sera of HIV-infected women

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.

CCR10 expression is required for immunogenicity of a HIV-1env DNA vaccine encoding CCL28 to enhance HIV-1env-specific IgG and IgA at relevant mucosal sites (VAC7P.986)

Development of a vaccine that drives anti-viral mucosal B cell responses is critical for protection against HIV-1 infection. It is currently unknown whether triggering CCR10/CCL28 pathways in a DNA-based vaccine results in induction of HIV-1env specific B cell immunity at mucosal sites of infection. We hypothesized that co-immunization with HIV-1env/CCL28 molecular adjuvant would augment B cell responses at gastrointestinal and vaginal sites and require CCR10. CCL28 co-immunized WT mice displayed a significant enhancement of HIV-1env specific antibody titers in serum, feces and vaginal washes, and enhanced HIV-1 specific IgA responses were abrogated in CCR10KO mice. CCL28 co-immunization did not increase the breadth of linear B cell epitopes in WT mice, but augmented the dominant epitopes elicited by antigen immunization alone. The frequency of splenic and intestinal IgA+CD19+B220+CD138+CCR10+ plasmablasts was augmented in the CCL28 co-immunized WT mice over antigen-only immunized WT controls. The physiological relevance of these findings was confirmed in a NHP model of intravaginal SIVsmE660 challenge in which CCL28 co-immunization resulted in significant increases in serum/vaginal IgG/IgA, decrease in peak viral loads, significant suppression of viral titers over 120 days, and recovery of CD4 T cells. These data support a role for CCL28 in targeting protective anti-viral B cells to mucosal sites when delivered as molecular adjuvants for HIV-1env DNA-based vaccines.

The Neonatal Fc receptor (FcRn) enhances human immunodeficiency virus type 1 (HIV-1) transcytosis across epithelial cells

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.

HIV-1 causes a sexually transmitted disease. However, the mechanisms employed by the virus to cross genital tract tissue and establish infection are uncertain. Since cervicovaginal fluid is acidic and HIV-1 in cervicovaginal fluid is likely coated with antibodies, we explored the effect of low pH and HIV-1-specific antibodies on transcytosis, the movement of HIV-1 across tight-junctioned epithelial cells. We found that the combination of HIV-1-specific antibodies and low pH enhanced transcytosis as much as 20-fold. Virus that underwent transcytosis under these conditions was infectious, and infectivity was highly influenced by whether or not the antibody neutralized the virus. We observed enhanced transcytosis using antibody from cervicovaginal and seminal fluids and using transmitted/founder strains of HIV-1. We also found that the enhanced transcytosis was due to the Fc neonatal receptor (FcRn), which binds immune complexes at acidic pH and releases them at neutral pH. Finally, staining of human tissue revealed abundant FcRn expression on columnar epithelial cells of penile urethra and endocervix. Our findings reveal a novel mechanism wherein HIV-1 may facilitate its own transmission by usurping the antibody response directed against itself. These results have important implications for HIV vaccine development and for understanding the earliest events in HIV transmission.

Comparative Evaluation of HIV-1 Neutralization in External Secretions and Sera of HIV-1-Infected Women

Objectives:

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).

Design:

Serum/plasma, CVL, and RL samples were examined by ELISA, WB and HIV-1 neutralization assays. Selected samples were Ig depleted and analyzed for virus neutralization.

Results:

IgG specific for three HIV-1 ENV antigens was detected in all serum/plasma samples, while IgA to at least one ENV glycoprotein was found at the low levels in 95% samples. Serum/plasma samples had the ability to neutralize at least one of three clade B and two clade C viruses. The neutralizing titers were reduced significantly or became undetectable after IgG removal. In corresponding CVL and RL, HIV-1 ENV-specific IgG antibodies were readily detected compared to IgA. Furthermore, IgG in CVL had greater ability than IgA to reduce virus infectivity. The difference in HIV-1 neutralization before and after Ig depletion was not observed in RL, implying that innate humoral factors were involved in anti-HIV-1 activity.

Conclusions:

Results demonstrate that HIV-1-specific neutralizing antibodies are almost exclusively of the IgG isotype in serum/plasma and CVL samples. HIV-1-specific binding antibodies detected in RL are not responsible for neutralization activity, suggesting that the antibody-mediated virus neutralization in external secretions should be verified by means of a selective depletion of Ig.

IgA nephropathy: molecular mechanisms of the disease

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.

Glycosylation of IgA1 and pathogenesis of IgA nephropathy

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.

In vitro-generated immune complexes containing galactose-deficient IgA1 stimulate proliferation of mesangial cells

IgA nephropathy (IgAN) patients have elevated serum levels of immune complexes consisting of IgA1 with galactose-deficient hinge-region O-glycans (Gd-IgA1) and anti-glycan IgG. These immune complexes deposit in the kidney and activate mesangial cells. To confirm that the activity of these immune complexes depends on the interaction of Gd-IgA1 with anti-glycan IgG, we generated in vitro analogous immune complexes using Gd-IgA1 myeloma protein and anti-glycan IgG from cord blood of healthy women. The Gd-IgA1 and anti-glycan IgG from cord-blood serum formed IgA1-IgG immune complexes that resembled those in sera of patients with IgAN. Furthermore, the ability to activate cellular proliferation was dependent on a heat-sensitive serum factor. In summary, we developed a new protocol for in-vitro formation of IgA1-IgG immune complexes, thus providing a new tool for studies of the pathogenesis of IgAN.

Naturally occurring structural isomers in serum IgA1 o-glycosylation

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.

Menstrual blood as a potential source of endometrial derived CD3+ T cells

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, αEβ7 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.

The pathophysiology of IgA nephropathy

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.

Aberrant glycosylation of IgA1 and anti-glycan antibodies in IgA nephropathy: role of mucosal immune system

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.