Scarcity or absence of humoral immune responses in the plasma and cervicovaginal lavage fluids of heavily HIV-1-exposed but persistently seronegative women

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.

Identification and characterization of CMP-NeuAc:GalNAc-IgA1 alpha2,6-sialyltransferase in IgA1-producing cells

Glycosylation defects occur in several human diseases. In IgA nephropathy, IgA1 contains O-glycans that are galactose-deficient and consist mostly of core 1 alpha2,6 sialylated N-acetylgalactosamine, a configuration suspected to prevent beta1,3 galactosylation. We confirmed the same aberrancy in IgA1 secreted by the human DAKIKI B cell line. Biochemical assays indicated CMP-NeuAc:GalNAc-IgA1 alpha2,6-sialyltransferase activity in this cell line. However, a candidate enzyme, ST6-GalNAcI, was not transcribed in DAKIKI cells, B cells isolated from blood, or Epstein-Barr virus (EBV)-immortalized IgA1-producing cells from the blood of IgAN patients and healthy controls. Instead, ST6-GalNAcII transcription was detected at a high level. Expression of the ST6-GalNAcII gene and activity of the CMP-NeuAc:GalNAc-IgA1 alpha2,6-sialyltransferase were higher in IgA1-producing cell lines from IgAN patients than in such cells from healthy controls. These data are the first evidence that human cells that lack ST6-GalNAcI can sialylate core 1 GalNAc-Ser/Thr.

Reactivities of N-acetylgalactosamine-specific lectins with human IgA1 proteins

Lectins are proteins with specificity of binding to certain monosaccharides or oligosaccharides. They can detect abnormal glycosylation patterns on immunoglobulins in patients with various chronic inflammatory diseases, including rheumatoid arthritis and IgA nephropathy (IgAN). However, lectins exhibit binding heterogeneity, depending on their source and methods of isolation. To characterize potential differences in recognition of terminal N-acetylgalactosamine (GalNAc) on IgA1, we evaluated the binding characteristics of several commercial preparations of GalNAc-specific lectins using a panel of IgA1 and, as controls, IgA2 and IgG myeloma proteins. These lectins originated from snails Helix aspersa (HAA) and Helix pomatia (HPA), and the plant Vicia villosa (VV). Only HAA and HPA bound exclusively to IgA1, with its O-linked glycans composed of GalNAc, galactose, and sialic acid. In contrast, VV reacted with sugars of both IgA subclasses and IgG, indicating that it also recognized N-linked glycans without GalNAc. Furthermore, HAA and HPA from several manufacturers differed in their ability to bind various IgA1 myeloma proteins and other GalNAc-containing glycoproteins in ELISA and Western blot. For serum samples from IgAN patients, HAA was the optimal lectin to study IgA1 glycosylation in ELISA and Western blot assays, including identification of the sites of attachment of the aberrant glycans. The galactose-deficient glycans were site-specific, localized mostly at Thr228 and/or Ser230. Because of the heterogeneity of GalNAc-specific lectins, they should be carefully characterized with appropriate substrates before undertaking any study.

IgA-containing immune complexes in the urine of IgA nephropathy patients

BACKGROUND

Sera of IgA nephropathy (IgAN) patients contain high levels of circulating immune complexes composed of IgA1 molecules with aberrantly glycosylated hinge-region O-linked oligosaccharides and IgG or IgA1 antibodies with anti-glycan or anti-hinge-region peptide specificities. Due to damaged sieving properties of the glomerular capillary wall in IgAN, these immune complexes may appear in the urine.

METHODS

We collected urine samples from 29 patients with biopsy-proven IgAN (Group I), 27 proteinuric patients with non-IgA nephropathies (Group II) and 28 healthy volunteers (Group III). The levels of urinary IgA and IgG and IgA-IgG-containing immune complexes were measured by ELISA and standardized for urinary creatinine concentrations.

RESULTS

The urinary IgA and IgG levels were significantly higher in Groups I and II than in Group III. Although the excretion of IgA as a fraction of total urinary protein was not significantly greater in IgAN patients than in patients with other renal diseases, the excretion of aberrantly glycosylated IgA1 was observed by western blot in 68% of the IgAN patients but in none of the healthy controls. The urinary levels of IgA-IgG immune complexes were significantly higher in Group I than in Groups II (P < 0.01) and III (P < 0.05). There was no significant difference in the levels between Groups II and III. These immune complexes had a molecular mass between 650-850 kDa, as shown by size-exclusion chromatography.

CONCLUSION

The amounts of urinary IgA-IgG-containing immune complexes were significantly higher in patients with IgAN than in patients with non-IgA nephropathies or healthy controls.

Human Male Genital Tract Secretions: Both Mucosal and Systemic Immune Compartments Contribute to the Humoral Immunity

In contrast to numerous studies of female genital tract secretions, the molecular properties of Abs and the magnitude of humoral responses in human male genital tract secretions to naturally occurring Ags and to mucosal and systemic immunizations have not been extensively investigated. Therefore, seminal plasma (SP) collected from healthy individuals was analyzed with respect to Ig levels, their isotypes, molecular forms of IgA, and for the presence of Abs to naturally occurring Ags, or induced by systemic or mucosal immunizations with viral and bacterial vaccines. The results indicated that in SP, IgG and not IgA, is the dominant Ig isotype, and that IgM is present at low levels. IgA is represented by secretory IgA, polymeric IgA, and monomeric IgA. In contrast to the female genital tract secretions in which IgA2 occurs in slight excess, the distribution of IgA subclasses in SP resembles that in plasma with a pronounced preponderance of IgA1. The IgG subclass profiles in SP are also similar to those in serum. Thus, SP is an external secretion that shares common features with both typical external secretions and plasma. Specifically, SP contains naturally occurring secretory IgA Abs to environmental Ags of microbial origin and to an orally administered bacterial vaccine, and plasma-derived IgG Abs to systemically injected vaccines. Therefore, both mucosal and systemic immunization with various types of Ags can induce humoral responses in SP. These findings should be considered in immunization strategies to induce humoral responses against sexually transmitted infections, including HIV-1.

Increased levels of galactose-deficient IgG in sera of HIV-1-infected individuals

BACKGROUND

The IgG from sera of patients with chronic inflammatory diseases of autoimmune character or some chronic microbial infections is frequently deficient in galactose on N-linked glycans. However, this phenomenon has not been investigated at length in human viral infections.

OBJECTIVES

To evaluate the glycosylation of serum IgG in HIV-1-positive patients.

METHODS

Psathyrella velutina lectin was used in enzyme-linked immunosorbent and Western blot assays to determine glycosylation. In addition, gas-liquid chromatography and mass spectrometry were utilized to confirm the galactose deficiency observed in the lectin-binding assays.

RESULTS

HIV-1-infected individuals had significantly higher levels of galactose-deficient IgG than healthy controls. In fact, the galactose deficiency of the N-linked glycans observed in other diseases was even more profound in HIV-1 infection. This deficiency was primarily restricted to IgG when total serum glycoproteins were evaluated and IgG1 was the subclass most affected in all patients. Also, a significant increase in lectin binding was observed on IgG2 and IgG4 from HIV-1-positive females compared with HIV-1-negative females.

CONCLUSIONS

Identification of deficient galactosylation of serum IgG from HIV-1-infected patients extended the spectrum of diseases in which this phenomenon has been observed. In addition, the results suggest yet another aspect of immune dysfunction as a result of HIV-1 infection.

Determination of aberrant O-glycosylation in the IgA1 hinge region by electron capture dissociation fourier transform-ion cyclotron resonance mass spectrometry

In a number of human diseases of chronic inflammatory or autoimmune character, immunoglobulin molecules display aberrant glycosylation patterns of N- or O-linked glycans. In IgA nephropathy, IgA1 molecules with incompletely galactosylated O-linked glycans in the hinge region (HR) are present in mesangial immunodeposits and in circulating immune complexes. It is not known whether the Gal deficiency in IgA1 proteins occurs randomly or preferentially at specific sites. To develop experimental approaches to address this question, the synthetic IgA1 hinge region and hinge region from a naturally Gal-deficient IgA1 myeloma protein have been analyzed by 9.4 tesla Fourier transform-ion cyclotron resonance mass spectrometry. Fourier transform-ion cyclotron resonance mass spectrometry offers two complementary fragmentation techniques for analysis of protein glycosylation by tandem mass spectrometry. Infrared multiphoton dissociation of isolated myeloma IgA1 hinge region peptides confirms the amino acid sequence of the de-glycosylated peptide and positively identifies a series of fragments differing in O-glycosylation. To localize sites of O-glycan attachment, synthetic IgA1 HR glycopeptides and HR from a naturally Gal-deficient polymeric IgA1 myeloma protein were analyzed by electron capture dissociation and activated ion-electron capture dissociation. Multiple sites of O-glycan attachment (including sites of Gal deficiency) in myeloma IgA1 HR glycoforms were identified (in all but one case uniquely). These results represent the first direct identification of multiple sites of O-glycan attachment in IgA1 hinge region by mass spectrometry, thereby enabling future characterization at the molecular level of aberrant glycosylation of IgA1 in diseases such as IgA nephropathy.

Paucity of antigen-specific IgA responses in sera and external secretions of HIV-type 1-infected individuals

This study was undertaken to resolve existing controversies with respect to the detection of IgA HIV-1-specific mucosal antibodies in infected individuals. External secretions, including tears, nasal, rectal, and vaginal washes, saliva, semen, urine, and sera were obtained from 50 HIV-1-infected individuals and 20 controls using collection procedures that minimize the irritation of mucosal surfaces. Levels of total and antigen (gp120 and gp160)-specific antibodies of the IgG and IgA isotypes were measured by assays that proved reliable in a large multicenter study: quantitative ELISA and chemiluminescence-enhanced Western blot analyses. Although the levels of total IgG and IgA were increased or remained unchanged in body fluids of HIV-1-infected individuals as compared to the controls, HIV-1-specific IgA antibodies were either absent or present at low levels even in secretions with characteristically high relative contents of total IgA vs. IgG (saliva, tears, and rectal and nasal washes). In these secretions, HIV-1-specific IgG antibodies dominated. In assessing levels and frequency of detection of IgG antibodies, both female and male genital tract secretions, urine, and nasal wash were preferable to parotid saliva and especially to rectal wash. External secretions contained IgG antibodies to gp160> gp120> gp41 and p24; when present, IgA antibodies were predominantly directed at gp160. Analyses of peripheral blood antibody-secreting cells (ASC) isolated from the same individuals paralleled these serological findings: gp160-specific IgG-secreting ASC were dominant. Therefore, in striking contrast to other mucosally encountered microbial infections, HIV-1 does not induce vigorous specific IgA responses in any body fluid examined or in ASC in peripheral blood.

Heterogeneity of O-glycosylation in the hinge region of human IgA1

Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry was applied to studies of the molecular heterogeneity of desialylated human IgA1 hinge region glycopeptides released with two IgA1 proteases. Typically, the hinge region of an alpha1 chain contains three to five O-linked glycan chains. Variants of the hinge region peptides released from IgA1(Kni) myeloma protein carrying 0, 1, 2, or 3 GalNAc residues were observed in the mass spectra as well as the nonglycosylated peptide. Variable numbers of Gal residues indicated additional heterogeneity in O-glycosylation of IgA1. In the hinge region preparation from normal human serum IgA1, glycopeptides carrying 2, 3, 4, or 5 GalNAc residues with variable numbers of Gal residues were detected. In conclusion, our new approach using the site-specific cleavage with two IgA1 proteases allowed precise and sensitive MALDI-TOF mass spectrometric analysis of O-glycosylation heterogeneity in IgA1 hinge region.

False positivity of enzyme-linked immunosorbent assay for measurement of secretory IgA antibodies directed at HIV type 1 antigens

We have determined that polymeric IgA in saliva of HIV-1-uninfected individuals binds in varying degrees to components of culture supernatants containing HIV-1 recombinant proteins when ELISA is used for the determination. This finding did not extend to salivary IgG antibodies. Further, such problems were not encountered in Western blot. Binding did not appear to be mediated by salivary proteins known to bind to IgA, including secretory component, amylase, lactoferrin, lysozyme, galactosyl transferase, or secretory leukocyte protease inhibitor, and was not influenced by blocking reagents or by changes in secondary anti-IgA antibodies. Although these findings will not likely impact on the use of saliva as a diagnostic fluid for HIV-1 infection (the HIV-1 response in saliva is mostly of the IgG isotype), they indicate that assessments of this secretion as an indicator of IgA mucosal immune responses to HIV-1 vaccines should be undertaken with caution.

Carbohydrate heterogeneity of human myeloma proteins of the IgA1 and IgA2 subclasses

Comparative studies of the N-linked carbohydrate chains of human myeloma proteins of the IgA1 and IgA2 subclasses were performed. The N-linked carbohydrate chains were released by hydrazinolysis from the polypeptide backbone, converted to radioactive oligosaccharides by sodium borotritide reduction after N-acetylation and separated into one neutral and two acidic fractions by paper electrophoresis. The acidic oligosaccharides were completely converted to neutral oligosaccharides by sialidase treatment, indicating that they were sialyl derivatives. The neutral and sialidase-treated acidic oligosaccharides were further fractionated by Bio-Gel P-4 column chromatography. Structural studies of each oligosaccharide by sequential exoglycosidase digestion and methylation analysis revealed that human myeloma IgA proteins contained significant amounts of biantennary complex-type carbohydrate chains in addition to a small amount of the high mannose-type. The results indicated that the oligosaccharide structures of human IgA1 and IgA2 display a high degree of heterogeneity not only in the number of carbohydrate chains, but also in their composition.

Interactions of cell-surface galactosyltransferase with immunoglobulins

Detection of the activity of beta-1,4-galactosyltransferase (beta-1,4-GT) in suspensions of viable mouse hepatocytes, the human hepatoma cell line Hep G2, the human colonic adenocarcinoma cell line HT-29, the monocyte-like cell line U937, and human splenic B and T lymphocytes suggested the presence of beta-1,4-GT, in an enzymatically active form, on plasma membranes. The presence of beta-1,4-GT on cell surfaces was also indicated from the effect of trypsinization of live cells, which significantly reduced cell surface beta-1,4-GT activity, but did not affect the activity associated with cytoplasmic membranes. Furthermore, the presence of beta-1,4-GT on the cell surface was demonstrated by indirect immunofluorescence staining of cells with anti-beta-1,4-GT antibody. The detection of radioactivity in immunoglobulins (Ig) and their component chains after incubation with suspensions of intact cells in the presence of Mn2+ and UDP-[3H]-galactose, indicated that Ig molecules were galactosylated. In the absence of UDP-[3H]-galactose, beta-1,4-GT on cell surfaces, or immobilized on Sepharose-4B, formed stable complexes with galactose acceptors, including Ig. The efficiency of binding decreased in the order: J chain > alpha chain > mu chain > polymeric IgA2 > monomeric/polymeric IgA1 > IgM > IgG. Thus, beta-1,4-GT could act as a cell-surface receptor for Ig through a cation-dependent, lectin-like association of the beta-1,4-GT with the carbohydrate moieties of the Ig. This was confirmed by indirect surface immunofluorescence and radiolabeled ligand binding assays. The binding was inhibitable by EDTA, alpha-lactalbumin (in the presence of glucose), GlcNAc, or uridine 3',5'dialdehyde. At 37 degrees C, the apparent affinity constants and association rate constants of interaction between cell surface beta-1,4-GT on glutaraldehyde-fixed HT-29 and U937 cells and alpha 2 chain or monomeric IgA1 were in the range from 7.1 x 10(7) to 4.6 x 10(8) M-1 and from 1 x 10(5) to 3 x 10(6) M-1 s-1, respectively. The dissociation rate constants and half time of dissociation calculated from these data were in the range from 2.1 x 10(-2) to 5.0 x 10(-4) s-1 and from 33 to 1380 s, respectively. The number of alpha 2 or IgA1 molecules bound per HT-29 and U937 cell were in the range from 1.9 x 10(5) to 1.3 x 10(6). The binding of IgA by the cell surface beta-1,4-GT was not associated with internalization or the catabolic degradation of the ligand.

Interactions of galactosyltransferase with serum and secretory immunoglobulins and their component chains

Assay of the activity of beta-1,4-galactosyltransferase (beta-1,4-GT) revealed that in addition to serum, milk, colostrum, amniotic and cerebrospinal fluids and malignant effusions, this enzyme is present also in tears and saliva. Molecular-sieve chromatography of human colostral whey and serum and subsequent assay of beta-1,4-GT activity have shown that beta-1,4-GT was present as a free enzyme (55 kDa) and associated with components of larger molar mass. The elution pattern did not change when the chromatography was carried out in a buffer devoid of, or enriched with, Mn2+, a cofactor of beta-1,4-GT activity. However, the activity associated with the large molar mass components was absent when the chromatography was carried out in the presence of a chelating agent (EDTA). Analyses of the eluted material by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS-PAGE), and by immunodiffusion indicated that the major colostral component in beta-1,4-GT activity-containing fractions was secretory IgA (S-IgA); in addition, the beta-1,4-GT activity was detected in fractions that contained lactoferrin and alpha-lactalbumin. Interactions of beta-1,4-GT with S-IgA and lactoferrin in colostrum were also demonstrated by the detection of radioactivity in precipitin lines obtained by immunoelectrophoresis and autoradiography of the colostral whey after it had been incubated with UDP-[3H]-galactose. Furthermore, radioactively labeled S-IgA and alpha-chain were detected when colostral whey incubated with UDP-[3H]-galactose was analyzed by SDS-PAGE under non-reducing and reducing conditions, respectively. In serum, the beta-1,4-GT-binding components identified in fractions after molecular-sieve chromatography were IgG, IgA, IgM and transferrin. The binding of beta-1,4-GT to immunoglobulins (Ig) was also demonstrated by assaying the beta-1,4-GT activity associated with Sepharose-4B-immobilized Ig of various isotypes and molecular forms, which were incubated with colostral beta-1,4-GT in the presence of Mn2+. Beta-1,4-GT measured by enzyme activity was bound to these Ig in order: polymeric IgA2 > monomeric IgA1 = polymeric IgA1 = secretory IgA = pentameric IgM > IgG. Immobilized component chains, namely alpha, mu and J chains, bound beta-1,4-GT more effectively than native Ig. Incubation of the IgA1 myeloma protein with crude human colostral galactosyltransferase in the presence of UDP[3H]-galactose and Mn2+ resulted in galactosylation of both N- and O-linked carbohydrate side chains.(ABSTRACT TRUNCATED AT 400 WORDS)

Cytokine-induced immunoglobulin production in primary IgA nephropathy

Increased IgA synthesis probably plays a role in the pathogenesis of IgA nephropathy (IgAN). We investigated whether an increased sensitivity to the effect of various growth factor combinations leads to increased immunoglobulin synthesis by peripheral blood mononuclear cells (PBMC) from IgAN patients, in comparison to healthy controls. Although none of the growth factors studied (pokeweed mitogen [PWM], interleukin [IL]-2, IL-6, transforming growth factor-beta [TGF-beta], and combinations) led to greater IgA synthesis in IgAN patients than in controls, the IgA subclass ratio was shifted in favor of IgA1. In controls, but not in IgAN patients, IL-2 enhanced the production of IgA and IgA1 compared with media alone. This possibly reflects previous in vivo activation by IL-2 in IgAN patients. The suppressive effect of TGF-beta on immunoglobulin synthesis was modestly greater in IgAN patients than in controls. Increased production of IL-2 and perhaps other cytokines by T cells in vivo may be responsible for the elevated IgA immune response in these patients.

Transforming growth factor-beta inhibits the production of IgG, IgM, and IgA in human lymphocyte cultures

Transforming growth factor beta (TGF beta) has potent immunoregulatory effects acting on both T and B cells. It strongly inhibits secretion of IgG and IgM in human and murine B cell cultures, but has been shown to have an enhancing effect on IgA production in the mouse. We have studied the effect of TGF beta on the production of IgA in human lymphocyte cultures. The addition of TGF beta to pokeweed-stimulated peripheral blood lymphocytes resulted in a suppression of IgA production of both subclasses, similar in magnitude to the suppression of IgG and IgM production. Membrane IgA expression was not increased by culturing tonsillar lymphocytes with TGF beta. In conclusion, we find no evidence for a selective enhancing effect of TGF beta on IgA synthesis in humans, in contrast to the findings reported in mice.

The role of the liver in catabolism of mouse and human IgA

The fate of intravascular IgA which is produced in large quantities in humans and many animal species was investigated in vivo and in vitro with emphasis on the monomeric form of IgA. The site(s) of the catabolism of intravenously injected mouse monomeric IgA labeled with a residualizing tracer (dilactitol - 125I tyramine) was studied in mice. The greatest in vivo uptake of monomeric IgA was observed in the liver. In contrast to identically labeled IgG, liver accounted for more internal catabolism of monomeric IgA than all other tissues (spleen, muscle, skin, and kidney) combined. Although both parenchymal and nonparenchymal liver cells internalized monomeric IgA, hepatocytes were far more active. The uptake of monomeric IgA was primarily mediated by the asialoglycoprotein receptor. In humans, the particulate fraction of liver homogenates and a human hepatoma cell line (Hep G2) bound human IgA proteins of various molecular forms. Inhibition of the binding by desialylated glycoproteins, requirement for the presence of calcium, and the molecular properties of the IgA-binding protein from the plasma membrane of Hep G2 cells indicated that the binding was primarily mediated by the asialoglycoprotein receptor. IgA proteins bound by Hep/G2 cells were internalized and catabolized to low molecular weight fragments.

Receptor-mediated binding and uptake of immunoglobulin A by human liver

We have studied the molecular mechanisms of the binding and uptake of secretory and serum immunoglobulin A (IgA) of both subclasses (1 and 2) and molecular forms (monomer and polymer) by the particulate fraction of human liver homogenate and by a human hepatoma cell line (HepG2). Inhibition by asialoorosomucoid and the requirement for the presence of calcium indicated that the binding of secretory IgA and polymeric IgA1 was mediated by the asialoglycoprotein receptor. Secretory component, which functions as a receptor for polymeric IgA in several animal species, was detected in the epithelial cells of bile ducts, but not in hepatocytes. Secretory IgA and all molecular forms and subclasses of serum IgA were bound by HepG2 cells, which do not express secretory component. The requirement for the presence of calcium, the presence of a terminal galactose residue in IgA, and the molecular weight of the major plasma membrane protein responsible for binding (41,700 daltons) indicated the involvement of asialoglycoprotein receptor. Immunoglobulin A proteins bound by HepG2 cells were endocytosed and catabolized.

The stoichiometry of J chain in human secretory dimeric IgA

Dimeric human secretory IgA was completely reduced with mercaptoethanol and alkylated with [14C]iodoacetamide. The component polypeptide chains were separated by high performance gel filtration in 5 M guanidine HCl into two fractions: one containing secretory component (SC) + heavy (H) chains; and the second containing light (L) + J chains. L and J chains were subsequently separated by polyacrylamide gel electrophoresis in sodium dodecyl sulfate (SDS) or in alkaline urea. Calculations of the J chain stoichiometry in the dimeric secretory IgA (S-IgA) molecule were based on: the measurement of the ratio of radioactivities of SC + H chain and L + J chain-fractions or L chain- and J chain-fractions; the known stoichiometry of SC, H and L chains; and the known number of half-cystine residues in the component polypeptide chains of S-IgA molecule. The data demonstrated that one molecule of dimeric S-IgA contains approx. one J chain.

Urinary immunoglobulins in healthy individuals and children with acute pyelonephritis

Urine samples obtained from children with acute pyelonephritis and from healthy children and adults were analysed with regard to the molecular form and specific antibody activity of urinary immunoglobulins. The urinary IgA and IgG levels were quantified in unconcentrated urine by radioimmunoassay. The children with urinary tract infection had significantly higher levels of IgG and IgA than age-matched controls but not higher than healthy adults. After tenfold concentration, the urine was fractionated on an Ultrogel AcA 22 column, and the IgA, secretory IgA, and IgG in the fractions were determined by radioimmunoassay. IgA in urine from healthy adults was predominantly represented by polymeric IgA linked to secretory component; small quantities of monomeric IgA were also present. IgG eluted in the position of the serum standard. Increased proportions of IgG and monomeric IgA were found in the infected patients. Specific antibody activity of the IgG and IgA classes to antigens of the infecting Escherichia coli strain was detected in whole and in fractionated urine from children with acute pyelonephritis. The specific antibody activity in healthy adults and children was low.

IgA-mediated elimination of antigens by the hepatobiliary route

Polymeric IgA antibody mediates the transport of corresponding antigens, in the form of IgA immune complexes (IC), from the circulation into the bile, whereas monomeric IgA, IgG, and IgM are ineffective. Transport has been shown with dinitrophenyl albumin and bacterial polysaccharides such as pneumococcal SIII and C-substance. The process does not result in breakdown of the antigen, which can be detected in the bile in intact free and IgA-bound forms. Although IgG promotes clearance of antigen from the circulation mainly to the liver, only low levels of breakdown fragments are detectable in bile. In mice, the mechanism of IgA IC transport does not appear to involve Kupffer cells, the complement system, or the glycoprotein receptors on liver cells because attempts to block these systems failed to affect transport. The mechanism appears to be analogous to that for free IgA. Transport could be inhibited by antigen-nonspecific IgA, but not IgG or IgM. IgA IC were found in the bile but not in the saliva, milk, urine, or bronchial or intestinal washings. A similar pattern of appearance was seen when IgA alone was injected. Thus hepatobiliary transport appears to be the major pathway for the clearance of both IgA IC and free IgA from the circulation.

Biosynthesis of J-chain in human lymphoid cells producing immunoglobulins of various isotypes

The relationship between synthesis, secretion, and subcellular localization of J-chain, IgM, IgA, and IgG was investigated in cultures of PWM-stimulated human PBL and in lymphoblastoid cell lines. Cells were examined for surface, cytoplasmic, and secreted immunoglobulins (Igs) and J-chain by immunofluorescence and radioimmunoassay (RIA). By these techniques, J-chain was detected in cells that produce polymeric or monomeric Igs. In PWM-stimulated PBL the synthesis of J-chain paralleled the production of Igs. In both PWM-stimulated (for 2 days) and unstimulated PBL, equal proportions of free and disulfide-linked J-chain were found. Increased amounts of intracellular J-chain were produced at later stages in PWM-stimulated PBL and J-chain occurred mostly in a free form. In tissue culture fluids, J-chain was not secreted in a free form but was always disulfide-linked to polymeric Igs. In lymphoblastoid cell lines, J-chain was present in a disulfide-linked form in IgM and IGA producers, but in IgG cells and in an IgM cell line (DAUDI) that did not secrete IgM but expressed it on the cell membrane, intracellular J-chain was present in free form. Although various proportions of polymeric and monomeric IgA were seen in culture fluids from IgA-secreting cell lines, intracellular IgA occurred mostly in a monomeric form. Further studies revealed that the ability to produce polymers was not equally distributed among all cells and might vary according to their content of J-chain and stage of maturation. Subcellular fractionation and subsequent analyses for J-chain and Ig in PWM-stimulated PBL and in IgM or IgG-producing cell lines revealed that these proteins were associated with fractions that contained ribosomes, cell sap, and low molecular weight RNA. In lysates of IgG and J-chain producing cells grown in the presence of 3H-labeled amino acids, intracellular J-chain was not disulfide-linked to IgG.

Inhibition of the pokeweed mitogen-induced response of normal peripheral blood lymphocytes by humoral components of colostrum

Colostral whey at dilutions up to 1 : 100 inhibited both the uptake of tritium-labelled thymidine and the differentiation of pokeweed mitogen-stimulated peripheral blood lymphocytes from normal adults into immunoglobulin-containing plasma cells. Upon gel filtration (Sephadex G-200), inhibitory activity was associated with high molecular weight fractions. Secretory component, but not monomeric, polymeric or colostral IgA, IgM, IgG, lactoferrin, casein or alpha-lactalbumin, inhibited the response to mitogen. Supernatants from cultures of colostral cells did not induce the differentiation of adult peripheral or cord blood lymphocytes into IgA-containing cells and did not stimulate the uptake of tritium-labelled thymidine.

Shared idiotypes among anti-albumin antibodies of different species

A system designed to detect plasma cells that produce antibodies directed at autologous idiotypic determinants of anti-human serum albumin (HSA) antibodies in rabbits was used to determine whether anti-HSA antibodies of horse, goat, swine and chicken origin were cross-reactive with rabbit antibodies of the same specificity. Fluorochrome-tagged anti-HSA preparations of these diverse species were used to stain splenic plasma cells of HSA-immunized rabbits and a similarly immunized chicken. The degree of idiotypic cross-reactivity, as detected by binding of anti-HSA antibodies to anti-idiotype within plasma cells of HSA-immunized animals, was sometimes equal to autologous staining. However chicken anti-HSA, the most phylogenetically distant idiotype examined, was demonstrably less cross-reactive than that obtained from the other species. Likewise, chicken plasma cells usually did not bind mammalian anti-HSA antibodies to an appreciable degree, as compared with autologous staining. These findings provide evidence for serologic and possibly structural similarities of antibodies of the same specificity from different species.

IgA1 proteases from Haemophilus influenzae, Streptococcus pneumoniae, Neisseria meningitidis, and Streptococcus sanguis: comparative immunochemical studies

IgA1 proteases from H. influenzae, N. meningitidis, S. pneumoniae, and S. sanguis were compared with respect to site of cleavage in the IgA1 molecule and EDTA sensitivity. Proteases from S. sanguis and S. pneumoniae cleaved the Pro (227)-Thr (228) bond within the hinge region of the alpha 1 chain and were inhibited by EDTA. H. influenzae IgA1 protease cleaved the Pro (231)-Ser (232) peptide bond. The activity of IgA1 proteases from H. influenzae and N. meningitidis was unaffected by EDTA. Purified and denatured alpha 1 chain was cleaved only in the hinge region. Other component chains of secretory IgA (secretory component, light and J chains) were not susceptible. In addition to IgA1 protease, S. pneumoniae released exo- and endoglycosidases that removed a considerable portion of carbohydrate side chains of IgA1; this activity was absent from crude IgA1 protease preparations of the other three bacterial species. Association in vitro of polymeric IgA1 with SC did not inhibit the degradation of IgA1 proteases. The considerable resistance of secretory IgA to cleavage by IgA1 proteases may be explained in part by the presence of IgA1 protease-neutralizing antibodies in secretory IgA.

IgA1 proteases from Haemophilus influenzae, Streptococcus pneumoniae, Neisseria meningitidis, and Streptococcus sanguis: comparative immunochemical studies

IgA1 proteases from H. influenzae, N. meningitidis, S. pneumoniae, and S. sanguis were compared with respect to site of cleavage in the IgA1 molecule and EDTA sensitivity. Proteases from S. sanguis and S. pneumoniae cleaved the Pro (227)-Thr (228) bond within the hinge region of the alpha 1 chain and were inhibited by EDTA. H. influenzae IgA1 protease cleaved the Pro (231)-Ser (232) peptide bond. The activity of IgA1 proteases from H. influenzae and N. meningitidis was unaffected by EDTA. Purified and denatured alpha 1 chain was cleaved only in the hinge region. Other component chains of secretory IgA (secretory component, light and J chains) were not susceptible. In addition to IgA1 protease, S. pneumoniae released exo- and endoglycosidases that removed a considerable portion of carbohydrate side chains of IgA1; this activity was absent from crude IgA1 protease preparations of the other three bacterial species. Association in vitro of polymeric IgA1 with SC did not inhibit the degradation of IgA1 proteases. The considerable resistance of secretory IgA to cleavage by IgA1 proteases may be explained in part by the presence of IgA1 protease-neutralizing antibodies in secretory IgA.

Secretory component of epithelial cells is a surface receptor for polymeric immunoglobulins

Epithelial cells of human fetal intestines and of a colonic carcinoma cell line (HT-29) exhibited intracellular and surface binding of polymeric immunoglobulins of IgA and IgM classes; monomeric IgA and IgG did not bind to these cells. Secretory component was identified as the receptor involved in the immunoglobulin binding. This conclusion was confirmed by the following experiments: trypsin abrogated the surface binding of polymeric immunoglobulin, reappearance of surface secretory component (SC) restored immunoglobulin binding; the appearance of SC in developing fetal tissues coincided with their potential to bind polymeric immunoglobulin; anti-SC reagents inhibited the binding of immunoglobulins to epithelial cells; and SC-containing secretory IgA did not bind to the surface of HT-29 cells.

Molecular-cellular interactions in the secretory IgA system

1) SC receptors were not detected on the surface of human PBL before or after PWM stimulation or on the surface of established lymphoblastoid cell lines. 2) SC binding was detected in the cytoplasm of differentiated lymphoid cells. The majority of the SC-binding cells contained intracellular IgA. 3) The binding of polymeric IgA to the surface of human epithelial cells (colonic carcinoma HT-29) was dependent on the presence of SC. 4) These findings indicate that SC is a receptor and possible transport protein for polymeric immunoglobulins, but that it is not directly involved in the homing of the IgA precursor cells to secretory tissues.

Identification and properties of J chain isolated from catfish macroglobulin

After the cleavage of disulfide bonds of macroglobulin isolated from channel catfish (Ictalurus punctatus), an electrophoretically fast-moving polypeptide, which resembled human J chain, was released. On a Sephadex G-200 column equilibrated in 5 M guanidine, the elution position of the J chain overlapped with the descending part of the L chain peak. Further purification was achieved by DEAE ion-exchange chromatography. The isolated polypeptide, which had a molecular weight of 14,800 +/- 500, as determined ultracentrifugally by sedimentation equilibrium in 5 M guanidine, contained 7% carbohydrate with one residue of fucose, two of mannose, one of galactose, two of glucosamine, and one of sialic acid per chain. A comparison of catfish and human J chain amino acid analyses showed the former to have a higher content of serine, glycine, and phenylalanine and a lower content of aspartic acid, isoleucine, and arginine. Tryptic peptide maps of catfish and human J chains revealed very few common peptides. Rabbit and guinea pig antisera to human J chain did not cross-react with catfish J chain. Untreated, resuced and alkylated, S-sulfonated, or cyanogen bromide cleaved macroglobulin from the gar (Lepisosteus osseus) contained no polypeptide analogous to either catfish or human J chain by the criteria employed in this study.

Identification and Properties of J Chain Isolated from Catfish Macroglobulin

After the cleavage of disulfide bonds of macroglobulin isolated from channel catfish (Ictalurus punctatus), an electrophoretically fast-moving polypeptide, which resembled human J chain, was released. On a Sephadex G-200 column equilibrated in 5 M guanidine, the elution position of the J chain overlapped with the descending part of the L chain peak. Further purification was achieved by DEAE ion-exchange chromatography. The isolated polypeptide, which had a molecular weight of 14,800 ± 500, as determined ultracentrifugally by sedimentation equilibrium in 5 M guanidine, contained 7% carbohydrate with one residue of fucose, two of mannose, one of galactose, two of glucosamine, and one of sialic acid per chain. A comparison of catfish and human J chain amino acid analyses showed the former to have a higher content of serine, glycine, and phenylalanine and a lower content of aspartic acid, isoleucine, and arginine. Tryptic peptide maps of catfish and human J chains revealed very few common peptides. Rabbit and guinea pig antisera to human J chain did not cross-react with catfish J chain. Untreated, resuced and alkylated, S-sulfonated, or cyanogen bromide cleaved macroglobulin from the gar (Lepisosteus osseus) contained no polypeptide analogous to either catfish or human J chain by the criteria employed in this study.

Studies on Human Secretory Immunoglobulin A

Fragments produced by cyanogen bromide cleavage of human secretory IgA were fractionated before and after the splitting of disulfide bonds on Sephadex G-200 columns in 5 M guanidine · HCl. By electrophoretic, antigenic, amino acid, and carbohydrate analyses of individual fractions it was revealed that J chain was released as a result of cyanogen bromide cleavage. Secretory component remained associated with a large fragment(s) of α chain (approximately 80% the size of the original α chain) to which L chains were also linked. Data indicate that J chain and secretory component are linked to different cyanogen bromide fragments of the α chain(s) and are not mutually connected by disulfude bonds. Although J chain might mediate the binding of secretory component through a disulfide-bond interchange reaction, the J chain is not involved in direct bridging between secretory component and polymeric IgA molecules.

Site of J chain attachment to human polymeric IgA

A fragment containing J chain was released from human polymeric myeloma IgA protein by cyanogen bromide cleavage. The identity of the fragment was determined by its electrophoretic mobility and antigenic determinants. After purification by gel filtrations and DEAE-Sephadex chromatography, this fraction appeared similar (with respect to its amino acid and carbohydrate compositions and its peptide maps) to the J chain isolated from this IgA protein; the molecular weight was 17,000 +/- 100. Upon reduction and alkylation, with subsequent separation of peptides by gel filtration, three components were obtained: the largest component (molecular weight 13,400) corresponded to the N-terminal segment of J chain and contained a homoserine residue, the second corresponded to the C-terminal part of J chain with 13-18 amino acid residues, and the third corresponded to the C-terminal octapeptide of the alpha chain. The data indicate that J chain is attached to alpha chain(s) through the penultimate cysteine residue of the C-terminal octapeptide.

Studies on Human Secretory Immunoglobulin A

Secretory IgA (S-IgA), in dissociating media, released small portions of secretory component (SC) and light chains but no J chain. After oxidative sulfitolysis, or reduction and alkylation followed by gel filtration in 5 M guanidine-HCl, SC was eluted in the heavy chain fraction, and J chain in the light chain fraction. A considerable portion of SC and J chain was released by oxidative sulfitolysis in the absence of dissociating agents and separated by gel filtration in neutral buffer. Data indicate one SC and one J chain per molecule of 11S S-IgA. The proposed molecular formula is (α2L2)2J1SC1.

Method of Serum IgA Isolation

Although immunoglobulin A (IgA) is the second most abundant immunoglobulin in human serum, the isolation of large quantities of it in immunochemically pure form has been difficult. Fractionation procedures for purifying serum IgA have recently been reviewed by Vaerman (1). Because of the similarity between IgA and IgG, techniques based on net-charge and molecular-weight differences between the two give a low yield. Other methods, based on specific antigenic determinants of IgA, require a monospecific antiserum and its attachment to form an immunoadsorbent.

The method reported here used the F(ab′)2 fragment of antibody to IgA; the immune precipitate was dissociated in low pH buffer and the components were subsequently separated by gel filtration.

An antiserum specific for IgA was produced in the goat. Immunochemically pure secretory IgA (S-IgA) from human colostrum was mixed with complete Freund's adjuvant (2) and injected both subcutaneously and intramuscularly. Three immunizations, of 20 mg S-IgA each, were given 3 weeks apart.