Evaluation of thirty-one mouse monoclonal antibodies to human IgG epitopes

Reinforced antimyeloma therapy via dual-lymphoid activation mediated by a panel of antibodies armed with bridging-BiTE

Immunotherapy using bispecific antibodies including bispecific T-cell engager (BiTE) has the potential to enhance the efficacy of treatment for relapsed/refractory multiple myeloma. However, myeloma may still recur after treatment because of downregulation of a target antigen and/or myeloma cell heterogeneity. To strengthen immunotherapy for myeloma while overcoming its characteristics, we have newly developed a BiTE-based modality, referred to as bridging-BiTE (B-BiTE). B-BiTE was able to bind to both a human immunoglobulin G-Fc domain and the CD3 molecule. Clinically available monoclonal antibodies (mAbs) were bound with B-BiTE before administration, and the mAb/B-BiTE complex induced antitumor T-cell responses successfully while preserving and supporting natural killer cell reactivity, resulting in enhanced antimyeloma effects via dual-lymphoid activation. In contrast, any unwanted off-target immune-cell reactivity mediated by mAb/B-BiTE complexes or B-BiTE itself appeared not to be observed in vitro and in vivo. Importantly, sequential immunotherapy using 2 different mAb/B-BiTE complexes appeared to circumvent myeloma cell antigen escape, and further augmented immune responses to myeloma relative to those induced by mAb/B-BiTE monotherapy or sequential therapy with 2 mAbs in the absence of B-BiTE. Therefore, this modality facilitates easy and prompt generation of a broad panel of bispecific antibodies that can induce deep and durable antitumor responses in the presence of clinically available mAbs, supporting further advancement of reinforced immunotherapy for multiple myeloma and other refractory hematologic malignancies.

Antibody-Invertase Fusion Protein Enables Quantitative Detection of SARS-CoV-2 Antibodies Using Widely Available Glucometers

Rapid diagnostics that can accurately inform patients of disease risk and protection are critical to mitigating the spread of the current COVID-19 pandemic and future infectious disease outbreaks. To be effective, such diagnostics must rely on simple, cost-effective, and widely available equipment and should be compatible with existing telehealth infrastructure to facilitate data access and remote care. Commercial glucometers are an established detection technology that can overcome the cost, time, and trained personnel requirements of current benchtop-based antibody serology assays when paired with reporter molecules that catalyze glucose conversion. To this end, we developed an enzymatic reporter that, when bound to disease-specific patient antibodies, produces glucose in proportion to the level of antibodies present in the patient sample. Although a straightforward concept, the coupling of enzymatic reporters to secondary antibodies or antigens often results in low yields, indeterminant stoichiometry, reduced target binding, and poor catalytic efficiency. Our enzymatic reporter is a novel fusion protein that comprises an antihuman immunoglobulin G (IgG) antibody genetically fused to two invertase molecules. The resulting fusion protein retains the binding affinity and catalytic activity of the constituent proteins and serves as an accurate reporter for immunoassays. Using this fusion, we demonstrate quantitative glucometer-based measurement of anti-SARS-CoV-2 spike protein antibodies in blinded clinical sample training sets. Our results demonstrate the ability to detect SARS-CoV-2-specific IgGs in patient serum with precise agreement to benchmark commercial immunoassays. Because our fusion protein binds all human IgG isotypes, it represents a versatile tool for detection of disease-specific antibodies in a broad range of biomedical applications.

Validation and cross-reactivity pattern assessment of monoclonal antibodies used for the screening of donor-specific IgG antibody subclasses in transplant recipients

The screening for IgG subclass donor-specific antibodies (DSAs) in allograft recipients uses IgG1-4 subclass-specific monoclonal antibodies (mAbs) that should be mono-specific. The cross-reactivity discrepancies reported for IgG subclass-specific mAbs warranted a critical cross-reactivity pattern analysis of the IgG subclass-specific mAbs most commonly used to detect DSAs. We tested the reactivity of 2 anti-IgG1-, 3 anti-IgG2-, 1 anti-IgG3-, and 2 anti-IgG4-specific PE-conjugated mAbs against microbeads coated with IgG1-4 proteins separately. Each IgG subclass protein was coated at three densities on the beads (0.5, 1, and 2 μg of protein per 10⁶ beads), and the PE-conjugated mAbs were titrated from 0.04 μg/mL to 5 μg/mL. The IgG subclass reactivity of the sample was acquired on the Luminex multiplex platform. Among the IgG subclass-specific mAbs, only the anti-IgG3 (clone: HP6050) mAb was mono-specific. All other mAbs tested were binding to IgG subclass proteins other than their respective immunogen, thereby being cross-reactive. IgG subclass cross-reactivity patterns were dependent on the concentration of both IgG subclass-specific mAbs and IgG1-4 protein targets coated onto the beads. With the current IgG subclass mAbs available, 3 of the 15 possible combinations of IgG1-4 subclass protein could be identified. While the remaining 12 unique combinations cannot be distinguished clearly, 6 groups that corresponded to two different unique combinations of IgG1-4 subclass protein could be identified. The dilution of serum samples and IgG subclass-specific mAbs, other than the anti-IgG3 (clone: HP6050), must be further optimized before their implementation in IgG subclass DSA screening in allograft recipients.

Facile development of medium optimization for antibody production: implementation in spinner flask and hollow fiber reactor

Most bio-industrial mammalian cells are cultured in serum-free media to achieve advantages, such as batch consistency, suspended growth, and simplified purification. The successful development of a serum-free medium could contribute to a reduction in the experimental variation, enhance cell productivity, and facilitate biopharmaceuticals production using the cell culture process. Commercial serum-free media are also becoming more and more popular. However, the cell line secrets its own recombinant product and has special nutritional requirements. How can the composition of the proprietary medium be adjusted to support the specific cell's metabolism and recombinant protein? This article uses statistical strategies to modify the commercial medium. A design of experiments is adopted to optimize the medium composition for the hybridoma cell in a serum-free condition. The supplements of peptone, ferric citrate, and trace elements were chosen to study their impact on hybridoma growth and antibody production using the response surface methodology. The stimulatory effect of the developed formulation on hybridoma growth was confirmed by the steepest ascent path. The optimal medium stimulated the hybridoma growth and antibody production in three diverse systems: a static plate, an agitated spinner flask, and a hollow fiber reactor. The cells in the developed serum-free medium had a better antibody production as compared to that in the commercial medium in the hollow fiber reactor. Our results demonstrated that the facile optimization for medium and antibody production was successfully accomplished in the hybridoma cells.

Association of Household Food- and Drink-Sharing Practices With Human Herpesvirus 8 Seroconversion in a Cohort of Zambian Children

Background

Human herpesvirus 8 (HHV-8) infection occurs in early childhood and is associated with human immunodeficiency virus type 1 (HIV-1) infection and risk for Kaposi sarcoma, but behaviors associated with HHV-8 transmission are not well described.

Methods

We enrolled and followed a prospective cohort of 270 children and their household members to investigate risk factors for HHV-8 transmission in Lusaka, Zambia.

Results

We report an incidence of 30.07 seroconversions per 100 child-years. Independent risk factors for HHV-8 incident infection included having a child who shared utensils with a primary caregiver (hazards ratio [HR], 2.33; 95% confidence interval [CI], 1.49-7.14), having an increasing number of HHV-8-infected household members (HR, 1.27; 95% CI, 1.09-2.79), and having ≥5 siblings/children in the household (HR, 2.24; 95% CI, 1.03-4.88). Playing with >5 children a day was protective against infection (HR, 0.54; 95% CI, .33-0.89), as was increasing child age (HR, 0.96; 95% CI, .93-.99).

Conclusions

This is the first study to find a temporal association between limited child feeding behaviors and risk for HHV-8 infection. Child food- and drink-sharing behaviors should be included in efforts to minimize HHV-8 transmission, and households with a large number of siblings should receive additional counseling as childhood infections occur in the home context.

Seroepidemiologic survey of epidemic cholera in Haiti to assess spectrum of illness and risk factors for severe disease

To assess the spectrum of illness from toxigenic Vibrio cholerae O1 and risk factors for severe cholera in Haiti, we conducted a cross-sectional survey in a rural commune with more than 21,000 residents. During March 22–April 6, 2011, we interviewed 2,622 residents ≥ 2 years of age and tested serum specimens from 2,527 (96%) participants for vibriocidal and antibodies against cholera toxin; 18% of participants reported a cholera diagnosis, 39% had vibriocidal titers ≥ 320, and 64% had vibriocidal titers ≥ 80, suggesting widespread infection. Among seropositive participants (vibriocidal titers ≥ 320), 74.5% reported no diarrhea and 9.0% had severe cholera (reported receiving intravenous fluids and overnight hospitalization). This high burden of severe cholera is likely explained by the lack of pre-existing immunity in this population, although the virulence of the atypical El Tor strain causing the epidemic and other factors might also play a role.

A milk-free diet downregulates folate receptor autoimmunity in cerebral folate deficiency syndrome

In cerebral folate deficiency syndrome, the presence of autoantibodies against the folate receptor (FR) explains decreased folate transport to the central nervous system and the clinical response to folinic acid. Autoantibody crossreactivity with milk FR from different species prompted us to test the effect of a milk-free diet. Intervention with a milkfree diet in 12 children (nine males, three females; mean age 6y [SD 4y 11mo], range 1-19y), decreased autoantibody titer significantly from 2.08pmol of FR blocked per ml of serum (SD 2.1; range 0.24-8.35) to 0.35pmol (SD 0.49; range 0-1.32; p=0.012) over 3 to 13 months, whereas FR autoantibody titer increased significantly to 6.53 (SD 6.08; range 0.54-14.07; p=0.013) in nine children who were reexposed to milk for 6 to 14 weeks. In 12 children on a normal diet (eight males, four females; mean age 5y 5mo [SD 4y 1mo], range 1y 6mo-16y 4mo), the antibody titer increased significantly from 0.84pmol of FR blocked per ml (SD 0.39; range 0.24-1.44) to 3.04pmol (SD 1.42; range 0.84-6.01; p=0.001) over 10 to 24 months. Decreasing the autoantibody titer with a milk-free diet in conjunction with folinic acid therapy may be advocated for these patients.

The IgG subclass-specificities of anti-IFNβ antibodies change with time and differ between the IFNβ products in relapsing remitting multiple sclerosis patients

Anti-Interferon beta (IFNbeta) antibodies are frequently produced during treatment with IFNbeta in Multiple Sclerosis (MS) patients. In recent years, it has become clear that these antibodies cause a decrease in IFNbeta-induced biomarkers and in IFNbeta clinical efficacy. Anti-IFNbeta antibodies are mainly of the IgG isotype, which consists of 4 subclasses. In this study, we tested whether changes occurred in IgG subclasses over time. A series of sera from 21 IFNbeta-treated patients (11 IFNbeta-1a, 10 IFNbeta-1b) were analysed longitudinally using a capture ELISA. IFNbeta-1a treated patients had a restricted subclass distribution, whilst IFNbeta-1b-treated patients demonstrated a wider distribution. When compared to IFNbeta-1b-treated patients, IFNbeta-1a-treated patients had lower levels of total and subclass-specific IgGs against IFNbeta. In particular, antibody levels were markedly lower in the neutralizing antibody (NAb) negative (-) category of IFNbeta-1a-treated patients in comparison to the NAb-IFNbeta-1b-treated patients. The most striking observation of this study were the very low levels or complete absence of IgG3 subclass-specific antibodies to IFNbeta in IFNbeta-1a-treated patients. This difference in the levels of IgG3 may help to clarify the differences in the overall pattern of development of anti-IFNbeta antibodies in IFNbeta-1a-and IFNbeta-1b-treated patients.

Interference in microsphere flow cytometric multiplexed immunoassays for human cytokine estimation

The present study describes positive and negative interference of human cytokine measurement in multiplexed bead-based immunoassays. Significant differences in measured IL-6 and TNF-alpha values in 30 normal human plasma samples were apparent depending on whether measurements were with a 2-plex assay or embedded in a multiplex of 8-or more cytokine antibody pairs, as well as among the kits of 3-different vendors. Sample diluents containing proprietary blocking ingredients were shown to greatly affect the outcome of measured cytokine values. Additionally, recovery of IL-6 and TNF-alpha from spiked samples suggests significant negative interference from either endogenous antibodies, soluble receptors or anti-cytokine antibodies in 10% and 26% of samples, respectively. While it is evident that multiplexed immunoassays hold great promise for cytokine profiling, there are still important issues needing further study. Especially needed are universally optimized sample diluents, uniformly calibrated standards with mass values, and internal assay controls, which should greatly facilitate intralaboratory accuracy and precision and interlaboratory comparisons of cytokine measurements. Possible causes of interference and remedies are discussed.

Analysis of anti-protective antigen IgG subclass distribution in recipients of anthrax vaccine adsorbed (AVA) and patients with cutaneous and inhalation anthrax

The anti-PA IgG1, IgG2, IgG3, and IgG4 subclass responses to clinical anthrax and to different numbers of anthrax vaccine adsorbed (AVA, BioThrax) injections were determined in a cross-sectional study of sera from 63 vaccinees and 13 clinical anthrax patients. The data show that both vaccination with three AVA injections and clinical anthrax elicit anti-PA IgG1, IgG2, and IgG3 subclass responses. An anti-PA IgG4 response was detected in AVA recipients after the fourth injection. The anthrax lethal toxin (LTx) neutralization efficacy of sera from recipients who received 4 to > or =10 AVA injections did not vary significantly in relation to changes in distribution of anti-PA IgG1 and IgG4 subclasses.

Monoclonal antibodies to SARS-associated coronavirus (SARS-CoV): identification of neutralizing and antibodies reactive to S, N, M and E viral proteins

Monoclonal antibodies (Mabs) against the Urbani strain of the SARS-associated coronavirus (SARS-CoV) were developed and characterized for reactivity to SARS-CoV and SARS-CoV S, N, M, and E proteins using enzyme-linked immunoabsorbent (ELISA), radioimmunoprecipitation, immunofluorescence, Western Blot and microneutralization assays. Twenty-six mAbs were reactive to SARS-CoV by ELISA, and nine were chosen for detailed characterization. Five mAbs reacted against the S protein, two against the M protein, and one each against the N and E proteins. Two of five S protein mAbs neutralized SARS-CoV infection of Vero E6 cells and reacted to an epitope within amino acids 490–510 in the S protein. While two of the three non-neutralizing antibodies recognized at second epitope within amino acids 270–350. The mAbs characterized should prove useful for developing SARS-CoV diagnostic assays and for studying the biology of infection and pathogenesis of disease.

Mass value assignment of total and subclass immunoglobulin G in a human standard anthrax reference serum

An anti-Anthrax Vaccine Adsorbed (anti-AVA) standard human reference serum pool, AVR414, has been prepared, and the total and protective antigen (PA)-specific immunoglobulin G (IgG) were quantified. AVR414 was prepared by plasmapheresis of healthy adults who had received a minimum of four subcutaneous injections of AVA. Mass values (in milligrams per milliliter) for total IgG and IgG subclasses 1 to 4 were determined by radial immunodiffusion. Anti-PA-specific IgG assignment (in micrograms per milliliter) was done by consensus of two complementary approaches: homologous enzyme-linked immunosorbent assay (ELISA) with affinity-purified anti-PA IgG as a calibrator and summation of mean PA-specific IgG subclass concentrations determined by IgG subclass-specific ELISA using the United States National Reference Preparation for Human Serum Proteins as a standard. The total IgG concentration assigned to AVR414 reference serum was 8.33 mg/ml. IgG subclass concentrations were the following: for IgG1, 4.48 mg/ml; for IgG2, 3.35 mg/ml; for IgG3, 0.37 mg/ml; and for IgG4, 0.30 mg/ml. The assigned mass value for total anti-PA-specific IgG was 141.2 microg/ml. Anti-PA-specific IgG subclass concentrations were the following: for IgG1, 79.6 microg/ml; for IgG2, 35.3 microg/ml; for IgG3, 3.2 microg/ml; and for IgG4, 25.3 microg/ml. Human reference serum pool AVR414 will have direct application in the standardization of anthrax serological assays, in reagent qualification, and as a standard for quantification of PA-specific IgG in humans who have been vaccinated with or otherwise exposed to Bacillus anthracis PA.

Type 1 diabetes alters anti-hsp90 autoantibody isotype

The 90-kDa chaperon family includes heat shock protein (hsp) 90 and glucose-regulated protein (grp) 94. These proteins play an important role in normal cellular architecture, in the etiology of some autoimmune and infectious diseases and in antigen presentation to T cells. Owing to its role in autoimmunity, we explored anti-hsp90 autoantibody (hsp90AA) response in the sera of persons with type 1 diabetes, first-degree relatives (FDR) and in normal subjects. Significant high level of hsp90AA was found in FDR, but there was no significant difference between the normal and diabetic persons. The IgG1 and IgG3 isotypes of hsp90AA were higher in persons with type 1 diabetes and FDR than in normal subjects. We found a good correlation between hsp90AA measured by ELISA and RIA. A positive correlation between serum hsp90AA and glutamic acid decarboxylase (GAD65) autoantibody (GAA) was also observed. Hsp90AA positive sera from diabetic persons immunoblotted recombinant hsp90, GAD65 and corresponding proteins in islet lysates. Our study suggests that hsp90AA are present in normal, FDR and diabetic persons. However, there is a higher level of IgG1 and IgG3 isotypes of hsp90AA in FDR and type 1 diabetic subjects. Thus, autoimmunity leading to type 1 diabetes significantly alters the autoantibody isotype to autoantigens, such as hsp90.

Generation and characterization of a mouse monoclonal antibody with specificity similar to staphylococcal protein A (SPA)

Human IgG is comprised of four subclasses (IgG(1), IgG(2), IgG(3), and IgG(4)). Each subclass possesses different biological properties. One of the differential specificities of human IgG subclasses is binding of Fc fragment of IgG(1), 2, and 4 but, not IgG(3) to staphylococcal protein A (SPA). This study was conducted to produce, select and characterize a monoclonal antibody (MAb) recognizing human IgG subclasses with specificity similar to SPA. Splenocytes from Balb/c mice immunized with Fc fraction of a human IgG(1) myeloma protein were fused with Sp2/0 myeloma cells. Fused cells were grown in hypoxanthine, aminopterine, and thymidine (HAT) selective medium and cloned by limiting dilution assay. Antibody-secreting cells were screened by enzyme-linked immunosorbent assay (ELISA) and the specificity of secreted MAb was further analyzed, using a panel of purified myeloma proteins by ELISA and immunoblotting. A murine hybridoma designated 6F11E1 was obtained that secretes an MAb specific for the Fc fragment of the immunizing protein. This MAb reacts with isotypic epitope common to IgG(1), 2 and 4 subclasses. An allelic epitope linked to IgG(3) molecules is also recognized by 6F11E1. This pattern of reactivity was found to be highly similar to that of SPA. Our findings imply that similar or overlapping epitopes are recognized by 6F11E1 and SPA.

Progression to type 1 diabetes is associated with a change in the immunoglobulin isotype profile of autoantibodies to glutamic acid decarboxylase (GAD65). Childhood Diabetes in Finland Study Group

To investigate whether type 1 diabetes in man is associated with a preferential Th1/Th2 response, and whether autoantibodies to one of the main autoantigens would reflect such a response, we characterized the immunoglobulin isotype profile to the 65-kDa isoform of glutamic acid decarboxylase (GAD65) in siblings to IDDM patients. Samples obtained from affected subjects before and at clinical onset of IDDM, from unaffected individuals at high risk and at low risk and from healthy controls were studied. The immunoglobulin isotype profile in the siblings at low risk reflected a more immature, i.e., IgM and Th2 like, i.e., IgE response compared to the progressors and siblings at high risk, with significantly higher median levels of IgM and IgE. The rank order of anti-GAD65 immunoglobulin isotypes was similar in the siblings before and at clinical onset of IDDM, IgG1 > IgG4 > IgM > IgE > IgA > IgG3 > IgG2, but markedly different in the individuals at low risk, IgG1 > IgM > IgE > IgG4 > IgG3 > IgA > IgG2. Based on these observations, we suggest that progression to clinical onset of IDDM is associated with a maturation and a decrease in the Th2 immune response against GAD65; findings which could have implications for future intervention and prediction strategies.

Age-dependent Neisseria meningitidis serogroup C class-specific antibody concentrations and bactericidal titers in sera from young children from Montana immunized with a licensed polysaccharide vaccine

Neisseria meningitidis serogroup C bactericidal titers and class-specific enzyme-linked immunosorbent assay (ELISA) antibody concentrations were measured in sera from 173 children (1 to 5 years old) before and 6 weeks and 7 months following vaccination with a quadrivalent (A/C/Y/W-135) polysaccharide vaccine. The immune responses of the children were compared with those of 40 adults 6 weeks postvaccination. Both bactericidal titers and ELISA antibody concentrations were significantly higher in the adults than in the children (P < 0.05). In addition, the ratio of immunoglobulin G (IgG) to IgM was higher in the children than in the adults. With an ELISA total antibody concentration of >/=2 microg/ml used as a measure of seroconversion, >/=84% of the individuals from each age group responded to the serogroup C polysaccharide. However, with a >/=4-fold-increase in bactericidal titer used, only 18% of 1-year-olds, 32% of 2-year-olds, and 50 to 60% of 3-, 4-, and 5-year-olds seroconverted. The ELISA results suggest that >50% of all children retained >/=2 microg of total antibody per ml at 7 months postimmunization. However, the bactericidal titers suggest that <10% of children <4 years old retained a >/=4-fold increase at 7 months following vaccination. Of particular note, 59 of 79 sera (75%) from the 1- and 2-year-olds had high ELISA antibody concentrations (2 to 20 microg/ml) with no associated bactericidal titer (<1:8). Discordant results between bactericidal titers and ELISA antibody concentrations were not explained by the presence of IgA blocking antibody or relative levels of IgG and IgM. The bactericidal results show age-dependent differences in the production and retention of antibody in young children immunized with serogroup C polysaccharide; these differences are not evident with the ELISA data.

Production of monoclonal antibodies to six isotypes of horse immunoglobulin

Stable clones of 18 mouse hybridomas that produce monoclonal antibodies (MAbs) to six isotypes of horse immunoglobulin were produced. The number of hybridomas of different specificities are: four to IgGa, four to IgGb, one to IgGc, four to IgG(T), two to IgM, and three to IgA. The immunoglobulin isotypes purified from affinity columns bound with each MAb showed variable mobility in agarose-gel electrophoresis. Migration proceeded from the anode as: IgG(T), IgA, IgM, IgGc, IgGb and IgGa. The purified isotypes also demonstrated a single precipitin line when in immunoelectrophoresis against isotype-specific or polyclonal antisera, raised against the purified isotype or whole equine serum, respectively.

Noncomplement fixing, IgG4 autoantibodies predominate in patients with anti-epiligrin cicatricial pemphigoid

This study characterized the specific reactivity, IgG subclass, and complement fixing ability of anti-laminin-5 IgG from 12 patients with anti-epiligrin cicatricial pemphigoid. Circulating IgG from all patients bound the dermal side of 1 M NaCl split skin, immunoprecipitated laminin-5 produced by biosynthetically radiolabeled human keratinocytes, and (in 10 of 12 cases) immunoblotted the laminin-alpha3 subunit. Analysis of the distribution of IgG subclasses in these patients' circulating anti-laminin-5 autoantibodies by semiquantitative indirect immunofluorescence microscopy using the HP series of subclass-specific monoclonal antibodies revealed: (i) IgG4 predominant autoantibodies in seven of 11 sera; (ii) IgG1 and IgG2 at substantially lower levels in a smaller number of sera; and (iii) no specific IgG3 anti-laminin-5 autoantibodies in any patients. The same IgG4-dominant profile of anti-laminin-5 autoantibodies was found in enzyme-linked immunosorbent assay studies of purified human laminin 5. Direct immunofluorescence microscopy of six skin biopsies from three patients found that IgG4 was also the predominant subclass of IgG in epidermal basement membranes in situ. Consistent with these findings, sera from 11 of 11 patients with anti-laminin-5 IgG autoantibodies did not fix C3 to epidermal basement membranes in vitro. These immunochemical studies suggest that complement activation does not play a major role in the pathophysiology of this disease and that subepidermal blisters in these patients may develop via a direct effect of anti-laminin-5 IgG itself.

Use of recombinant Onchocerca volvulus antigens for diagnosis and surveillance of human onchocerciasis

The diagnostic value of ELISAs based on recombinant Onchocerca volvulus antigens OC 3.6 and OC 9.3 was evaluated with sera from endemic areas in West Africa, Guatemala and Ecuador. IgG assays were slightly more sensitive than those that detected IgG4, and the antigen combination was significantly more sensitive than either antigen alone (OC 3.6, 93%; OC 9.3, 84%, combined 98%). These assays were also evaluated with sera from 2 villages in the Onchocerciasis Control Programme area of West Africa including one village (Pendie) with recent recrudescence of infection and one (Niarba) where transmission had been interrupted for 15 years by vector control. The OC 3.6 IgG antibody assay was sensitive for new infections and exposure in Pendie; 24/24 (100%) of people with positive skin snips and 15/74 (20%) of sera from MF negative people had IgG antibodies to this antigen. In addition, antibodies to OC 3.6 often preceded the onset of skin snip positivity in Pendie. In contrast, IgG antibodies to OC 3.6 and OC 9.3 were rarely seen in children born during the 15 years since transmission was interrupted by vector control in Niarba. These encouraging results suggest that antibody assays based on OC 3.6 and OC 9.3 may be valuable tools for surveillance of onchocerciasis and also for monitoring the efficacy of control programmes.

Assignment of Neisseria meningitidis serogroup A and C class-specific anticapsular antibody concentrations to the new standard reference serum CDC1992

A new standard meningococcal reference serum designated CDC1992 was prepared to replace meningococcal reference sera ECG and PB-2, which are not available in sufficient quantities for continued use as primary reference sera. CDC1992 was prepared from 14 healthy adult volunteers who underwent plasmapheresis 4 to 12 weeks postvaccination with a single dose of a Neisseria meningitidis quadrivalent polysaccharide vaccine. Total and/or class-specific meningococcal serogroup A and C anticapsular antibody concentrations (in micrograms per milliliter) were assigned to CDC1992 by using homologous and heterologous enzyme-linked immunosorbent assay (ELISA) formats. The reference serum ECG was used as a reference standard to assign total anticapsular antibody concentrations to CDC1992 by a homologous ELISA format. A heterologous ELISA format, with the Haemophilus influenzae type b standard reference serum FDA 1983, was used to assign total and class-specific antibody concentrations to CDC1992. Alkaline phosphatase-labeled mouse anti-human monoclonal antibody conjugates were used as secondary antibodies in both ELISA formats. The total, immunoglobulin G (IgG), IgA, and IgM antibody concentrations, assigned to CDC1992 for serogroup A were 135.8, 91.8, 20.1, and 23.9 micrograms/ml, respectively, and those for serogroup C were 32.0, 24.1, 5.9, and 2.0 micrograms/ml, respectively. Meningococcal serogroup A and C antibody concentrations were in good agreement when homologous and heterologous ELISA format results were compared. Total and class-specific serogroup A and C antibody concentrations were determined in six adult quality control serum samples from the Centers for Disease Control and Prevention by using the homologous ELISA and our assigned antibody concentrations for CDC1992. Antibody concentrations in reference sera ECG and PB-2 were measured in order to provide a historical link to previous studies. The general acceptance of CDC1992 as the standard reference serum and the assigned antibody concentrations will allow investigators to compare antibody levels in serum to those in a single reference preparation.

Immunoglobulin G1 (IgG1) and IgG3 antibodies are markers of progressive disease in leprosy

Mycobacterium leprae-specific and polyclonal immunoglobulin G (IgG) subclass and IgE antibodies in leprosy patients across the histopathological spectrum were determined by using a quantitative enzyme-linked immunosorbent assay. Antibody responses to M. leprae sonicates were detected only in IgG1, -2, and -3 subclasses. Even at 100-times-lower dilutions, very little IgG4 and IgE antibody activity against M. leprae was detected in any group of leprosy patients. Quantitatively, antibody responses were highest at the lepromatous pole and decreased towards the tuberculoid pole. The greatest quantitative difference in antibodies between the lepromatous and tuberculoid poles was observed with IgG1 (140-fold), this was followed by the difference with IgG3 antibodies (32-fold). Polyclonal antibodies, on the other hand, were elevated for all four IgG subclasses as well as IgE in both lepromatous and tuberculoid leprosy patients compared with healthy controls from a leprosy-endemic area. Selective elevation of M. leprae-specific antibody responses in IgG1 and IgG3 subclasses, therefore, could not be attributed to selective polyclonal activation in these particular subclasses. Furthermore, polyclonal activation for IgE was observed in both lepromatous and tuberculoid leprosy patients, with higher levels in the tuberculoid group, which does not support selective TH2 activation in lepromatous leprosy patients. IgG1 and IgG3 antibodies also showed the highest Spearman rank correlation with the bacterial index in these patients (rho = 0.748 and P < 0.001 for IgG1; rho = 0.721 and and P < 0.001 for IgG3). Thus, disease progression in leprosy showed a significant correlation with selective increases in IgG1 and IgG3 responses.

IgE+ cells in the peripheral blood of atopic, nonatopic, and bee venom-hypersensitive individuals exhibit the phenotype of highly differentiated B cells

We have analyzed IgE+ cells in peripheral blood of atopic donors, donors hypersensitive to bee venom, and nonatopic control donors with two- and three-color flow cytometry. Although the percentage of IgE+ cells varied among these groups, the overall phenotypic patterns were similar. Most IgE+ cells do not display typical B-cell markers, such as CD19, CD20, and CD21. A significant proportion of these cells stain for CD38, indicating that they are more differentiated. IgE+ cells express Fc gamma RII and CD45RO, an isoform associated with an advanced level of differentiation. The majority of IgE+ cells do not coexpress other surface immunoglobulin isotypes. In the case of bee venom-hypersensitive donors, we have been able to identify a small population of IgE+ cells with a specificity for phospholipase A2, a major immunogenic component of bee venom. The phospholipase A2+ cells display a phenotype similar to that of the IgE+ cells.

Molecular cloning of Brugia malayi antigens for diagnosis of lymphatic filariasis

Immunological crossreactivity among nematodes has hampered development of specific serodiagnostic assays for lymphatic filariasis. In the present study, we report the molecular cloning and characterization of two filaria-specific recombinant clones (BmM5 and BmM14) with immunodiagnostic potential. BmM5 is a 505-bp cDNA which codes for a protein of 130 residues that ends with an endoplasmic reticulum targeting sequence. BmM14 is closely related to a recently reported clone (SXP-1), and it has 62% homology (deduced amino acid sequence) with a previously described Onchocerca volvulus clone, lambda RAL-2. Glutathione S-transferase fusion proteins of BmM5 and BmM14 were tested in various ELISA formats. The best results were obtained by measuring IgG4 antibodies to the fusion proteins. ELISA studies showed that approximately 90% of 111 sera from Indian and Egyptian patients with brugian and bancroftian filariasis were reactive with both antigens. Nonendemic sera as well as sera from patients with schistosomiasis or intestinal helminths were uniformly nonreactive. Assays based on BmM5 and BmM14 may be useful for large scale screening as an alternative to microfilaria or filarial antigen detection as a means of obtaining a rough index of filariasis endemicity in previously unstudied areas.

Heterogeneity of bovine IgG2. VI. Comparative specificity of monoclonal and polyclonal capture antibodies for IgG2a (A1) and IgG2a (A2)

The relative specificity of 26 randomly selected polyclonal and monoclonal anti-bovine IgG2 reagents for the A1 and A2 allotypic variants of IgG2a was evaluated in a direct RIA using the reagents as solid-phase capture antibodies (CAbs). More than 70% of these reagents were significantly allotype-biased and > 80% of those were positively biased to IgG2a (A1). Compared as the ratio of the ng of IgG2a (A1) bound versus ng IgG2a (A2) bound per 50 ng added (Krel), bias for IgG2a (A1) of six of these reagents was greater than two-fold. Compared in terms of their solid-phase equilibrium constants (Keq), differences as great as two-logs among these reagents were observed. Steward-Petty plots suggested that differences in Krel of a select panel of reagents was usually due to differences in Keq, but for two reagents with large differences in Krel, the existence of one population of CAbs recognizing an allotope and another recognizing common IgG2a determinants, was indicated. Eight of ten guinea pigs immunized with IgG2a (A1) responded with highly significant specificity bias for A1 whereas only two of 11 rabbits and two of ten guinea pigs immunized with IgG2a (A2) responded weakly with preference for IgG2a (A2). These results concur with the concept of the immunodominant nature of the A1 allotope, but also suggest that immunization with IgG2a (A2) might be a practical means of avoiding allotype bias in IgG2a reagents. The data indicate that the majority of randomly selected anti-bovine IgG2 reagents are allotype biased to the extent that when used as serological reagents to measure total IgG2 or bovine IgG2 antibody responses, the allotype of the animal tested rather than its total IgG2a concentration or IgG2 antibody titer, can determine the outcome of the serological test.

Cross-reactivity of 75 monoclonal antibodies to human immunoglobulin with sera of non-human primates

We systematically analyzed a panel of 75 murine monoclonal antibodies (mAbs) reactive with human immunoglobulins IgG, IgA, IgM, IgD, and kappa and lambda light chains for reactivity with serum immunoglobulins of higher primates. In the great apes, and to a lesser extent in other primates, epitopes related to human light chains, IgM, IgA, IgD, and all 4 IgG subclasses were identified with many of the mAbs. Those mAbs identified as reactive with a given species may be useful for immunologic studies of these species. Cladistic analysis of antigenic relatedness generated a phylogenetic tree consistent with current anatomic or molecular taxonomies.

Preliminary evaluation of recombinant Onchocerca volvulus antigens for serodiagnosis of onchocerciasis

Serodiagnostic assays for onchocerciasis based on native antigens are hampered by the scarcity of antigen, and they suffer from poor specificity. The present study was designed to evaluate the diagnostic utility of recently described recombinant Onchocerca volvulus antigens OC 3.6 and OC 9.3 in enzyme immunoassays. The recombinant proteins were expressed as glutathione S-transferase fusions and were tested in several enzyme immunoassay formats to measure immunoglobulin G (IgG) and IgG4 antibodies with sera from patients with onchocerciasis in Nigeria and with various types of control sera. The best results were obtained by measuring IgG4 antibodies to the fusion proteins. Forty of 42 (95%) serum specimens from patients with onchocerciasis were reactive with OC 3.6; the reactivity with OC 9.3 was 81%. Results obtained with sera from experimentally infected chimpanzees suggest that OC 3.6 might be especially useful for detecting prepatent infections in humans, while OC 9.3 mainly detects mature, patent infections. Sera from individuals in Nigeria and the United States residing in areas nonendemic for onchocerciasis were uniformly nonreactive with these antigens in IgG and IgG4 assays, as were sera from patients with bancroftian filariasis, brugian filariasis, loiasis, ascariasis, schistomiasis, and dracunculiasis. These results suggest that enzyme immunoassays based on the recombinant antigens OC 3.6 and OC 9.3 are useful for the diagnosis of onchocerciasis.

Epitope mapping of human immunoglobulin-specific murine monoclonal antibodies with domain-switched, deleted and point-mutated chimeric antibodies

27 engineered chimeric antibodies possessing human gamma, epsilon, mu or alpha constant regions and V region specificity for nitrophenyl or dansyl were used to study the isotype specificity of 29 murine monoclonal antibodies (MAbs) specific for human immunoglobulins (IgG1-4, IgE, IgM, IgA or secretory piece). The isotype-restricted immunoreactivity observed with wild-type chimeric antibodies paralleled the pattern of each MAb's reactivity with purified human myeloma proteins. 16 mutant IgG anti-dansyl chimeric antibodies with genetically engineered domain switches, deletions or point-mutations were used as antigens to further characterize the epitopes recognized by the human IgG subclass-specific MAbs. The binding of three human IgG1-specific MAbs (HP6069, HP6070 and HP6091) was mapped to similar epitopes on the CH2 domain of human IgG1. Of the two anti-human IgG2 MAbs tested, HP6002 reacted with the CH2 of IgG2 while HP6014 bound to the CH1 domain. Both anti-human IgG3 MAbs (HP6047, HP6050) reacted with different regions of the IgG3 hinge. The anti-human IgG4 MAbs (HP6023, HP6025) bound to a similar epitope on the carboxyl terminus of CH2 or the CH3 of human IgG4. The three exclusion antibodies (HP6019, HP6030 and HP6058) bound to different epitopes in the CH2 domain of three of four IgG subclasses. The domain mapping was confirmed by competitive inhibition experiments. These results were used to select a group of IgG-reactive MAbs for construction of a poly-monoclonal anti-IgG capture and detection reagent that uniformly bound all four subclasses of human IgG. This study provides support for the use of engineered chimeric human chimeric antibodies as replacements for increasingly rare, purified human paraproteins in the specificity analysis of immunochemical reagents used in clinical and research laboratories for the detection and quantitation of human antibodies. Moreover, these studies demonstrate how the MAbs can serve as effective probes for examining conformational differences among the four human IgG subclasses.

An immunoblotting procedure following agarose gel electrophoresis for subclass typing of IgG paraproteins in human sera

A method for subclass typing of IgG paraproteins in human sera following agarose gel electrophoresis is presented. After electrophoretic separation, serum proteins were blotted by capillary diffusion onto nitrocellulose. Mouse anti-human IgG1-IgG4 monoclonal antibodies were exposed to bound IgG. Goat anti-mouse IgG alkaline phosphatase conjugate was employed as second antibody. Thirty six sera were examined, in which the presence of an IgG paraprotein had previously been proved by agarose gel electrophoresis and subsequent immunofixation with anti-IgG antiserum. The subclass frequency distribution was 27 IgG1, 6 IgG2, 2 IgG3 and 1 IgG4. By means of IgG subclass typing in 8 out of these 36 sera, a total of 12 additional monoclonal bands (1 to 2 bands per serum) were detected which were not seen after immunofixation electrophoresis with anti-IgG antiserum. Eleven of 12 additional bands belonged to an IgG subclass different from that of the bands already detected by immunofixation electrophoresis. Light chain typing was performed in 9 of 12 bands found additionally. Two of these 9 bands belonged to a light chain class different from that of the bands already detected by immunofixation electrophoresis. The method described can be employed to further elucidate the possible diagnostic and prognostic significance of the subclass type of an IgG paraprotein.

Immunoglobulin class and IgG subclass distribution of anticardiolipin antibodies in patients with systemic lupus erythematosus and associated disorders

The class and subclass distribution of an antibody response may give insight into the stimulating mechanism and likely effector functions. IgA, IgG and IgM anticardiolipin antibodies (aCL) were quantified in a consecutive series of 200 samples sent to an autoimmune serology laboratory to determine the relationships between aCL responses of each of these antibody classes and, in particular, whether there was any utility in the measurement of IgA aCL. Positive results for one of the three aCL isotypes were found in 105 samples (53%), and in 41 samples IgA aCL was detected (21%). However, amongst these unselected samples, little additional information was obtained by measurement of IgA aCL, which was found in conjunction with IgM or IgG aCL in all but five samples, and in these the isolated elevation of IgA aCL was only slight, and showed no disease specificity. The levels of each of the four IgG subclasses of aCL were measured in a subgroup of serum samples from 28 patients with autoimmune disease and from 29 patients with syphilis. Amongst the SLE patients IgG1 and IgG3 aCL were the predominant IgG subclasses, consistent with an antigen-driven, T cell-dependent antibody response. However, a subgroup of eight of the autoimmune subjects had predominant elevation of IgG2 aCL, possibly implying a role for T cell-independent antibody production to cardiolipin. Amongst the syphilis patients IgG1 and IgG3 aCL were also the predominant subclasses of aCL but IgG4 aCL were also detected in the majority of subjects, consistent with prolonged antigenic stimulation.

Pregnant women with endemic pemphigus foliaceus (Fogo Selvagem) give birth to disease-free babies

Endemic pemphigus foliaceus (PF), also known as Fogo Selvagem (FS), is an organ-specific autoimmune disease mediated by autoantibodies. These autoantibodies are disease specific, predominantly restricted to the IgG4 subclass, and pathogenic, as demonstrated by passive transfer studies. In contrast to pemphigus vulgaris, neonatal skin disease does not appear to occur in babies born to mothers with non-endemic PF or FS. In the present study we have examined 19 mother/neonate pairs where the mother had documented FS. Mothers and neonates were examined soon after delivery and tested by immunofluorescent (IF) techniques for FS autoantibodies either in circulation (mothers' sera or babies' cord blood) or bound to the neonatal epidermis. All neonates included in this study were born with normal skin. Twelve biopsies from 17 neonates showed negative direct IF using both FITC-antihuman IgG or monoclonal anti-IgG subclass antibodies. In five biopsies the epidermal ICS of the babies showed weak staining. In 10 of the 19 cord sera tested, FS IgG autoantibodies were undetectable; in nine, these autoantibodies were present in low titers (less than 1:40). The sera of the mothers showed higher titers of FS autoantibodies, and IgG4 was the predominant IgG subclass autoantibodies. It appears that human placenta may modulate the expression of disease in the newborn by operating as a "biologic immunoadsorbent" of pathogenic autoantibodies.

Immunoglobulin class and subclass-specific monoclonal antibody sandwich ELISA for the detection of antibodies against coxsackieviruses B, types 1-5

Immunoglobulin subclass-specific ELISAs were developed for human IgG1, IgG2, IgG3, IgG4, IgAtotal, and IgM directed against Coxsackie B (CB) virus types 1, 2, 3, 4, and 5. In all the assays the solid phase was coated with immunoglobulin class/subclass-specific monoclonal antibodies, followed by an incubation with the serum specimens. Incubation with one of the CB viruses, as well as an incubation with biotinylated serotype-specific monoclonal antibodies to the same virus type provided the virus specificity. Finally, there were incubations with peroxidase labeled Extravidin and the substrate-chromogen system. This ELISA method eliminated the competition between the immunoglobulin classes and subclasses. IgG3 and/or IgG1 were seen most frequently of the IgG subclasses, but IgG2 and IgG4 were also present infrequently. The viral specificity of the antibody subclass assays seems to be predominantly at the enterovirus group level, but this remains to be evaluated in a larger study. IgA and IgM were seen almost exclusively in specimens from patients with acute enteroviral infections, except in the assays with the crude CB5 antigen. This indicates the possible suitability of the IgA and IgM assays as diagnostic tests for enteroviral infections. A larger study is necessary to confirm this finding.

Evaluation of monoclonal antibodies having specificity for human IgG subclasses: results of the 2nd IUIS/WHO collaborative study

Following the 1st IUIS/WHO Collaborative Study of monoclonal anti-IgG subclass antibodies, a panel of WHO Specificity Reference Reagents (SRR) was established [Jefferis, R., et al. (1985) Immunol. Lett., 10, 223]. At the time, the hope was expressed that further reagents particularly for IgG2, and other allotypic specificities would become available which could be applied in a wide range of assay protocols. The 2nd study reports the evaluation of nineteen anti-subclass and seven anti-allotype monoclonal antibodies. The anti-IgG1 antibody HP6187 was equivalent in performance to the SRR. Others, that were not of the mouse IgG1 isotype, may be useful for particular applications. The anti-IgG2 antibody HP6200 could be a valuable addition to the WHO SRR; it is specific for an epitope in the Fab region but does not have the light chain bias of HP6014. Antibodies of putative allotype specificity exhibited the claimed specificity when used within protocols similar to those employed by the originating laboratory. It appears to be inherent in the nature of the epitopes (allotopes) recognized that it will take several years before reagents applicable to a wide range of techniques will become available.

Methodological pitfalls in serum IgG2 level measurements by immunoenzymatic assays with monoclonal antibodies

Four anti-IgG2 monoclonal antibodies (Mabs) were evaluated for their reactivity with purified myeloma IgG2 of different light chain types and Gm allotypes in three distinct immunoenzymatic assays (ELISA). The reactivity of three Mabs with solid-phase antigens was similar whereas an anti-Fab antibody (clone HP 6114) predominantly bound IgG2 kappa. In competitive and immunometric (sandwich type) assays, the binding of the two anti-IgG2 Mabs (HP 6014 and HP 6114) reacting with epitopes located on the Fab fragment was strongly influenced by the light chain type of IgG2 and by other factors (probably including differences in the variable regions); the Mab HP 6114 reacted virtually only with IgG2 kappa whereas the Mab HP 6014 displayed a much stronger affinity for IgG2 lambda than for IgG2 kappa; for both anti-Fab Mabs, important differences were found in their binding to individual IgG2 proteins. In addition, the Mab HP 6014 seemed to show a slightly better affinity for IgG2 bearing the Gm(23) allotype. These results urge much caution in IgG2 level measurement, especially with commercial kits, most of which use the Mab 6014 as the single anti-IgG2 reagent.

The distribution of IgG subclass autoantibodies in bullous pemphigoid analysed by immunofluorescence and immunoblotting

The distribution of IgG subclasses in bullous pemphigoid (BP) autoantibodies in 14 BP sera and four biopsies was analysed by immunofluorescence (IF) and immunoblotting (IB). Three clones of monoclonal antibodies (MoAbs) to each IgG subclass were used. All 14 sera showed linear fluorescence in the basement membrane zone with IF, and 240 kDa and/or 180 kDa protein bands in human epidermal extract were detected by IB using a polyclonal antibody to total IgG. BP antibody in IgG4 subclass was found to be predominant, as it was detected most frequently and intensively in all positive sera and lesions studied by both techniques. In the IgG1 to IgG3 subclasses, a range of proportions of positive sera was obtained among MoAbs to the same IgG subclass in both techniques. However, one MoAb could detect IgG1 subclass BP antibody with a high frequency in both techniques. No difference in IgG subclass distribution of BP antibodies was observed during the course of the disease. In each serum, any IgG subclass of BP antibody recognized the identical BP antigen(s). These results suggest the predominance of IgG4 subclass and the possible presence of IgG1 subclass in BP antibodies.

IgG subclass responses to human immunodeficiency virus-1 antigens: lack of IgG2 response to gp41 correlates with clinical manifestation of disease

To analyze differential antibody responsiveness of potential pathogenetic significance, sera from 66 patients with human immunodeficiency virus-1 (HIV-1) infections at various Walter Reed (WR) stages of the disease were analyzed to determine the subclass distribution of HIV antibodies. Although all IgG subclasses were involved in the HIV antibody response, the frequency was highest for IgG1 and the lowest for IgG4. When IgG subclass responses to different HIV antigens were compared qualitatively, IgG1 was the major subclass reactive with env, pol, and gag antigens; IgG2 and IgG3 were almost equally represented in response to gag gene products; and IgG4 showed minimal reactivity to p24 antigen in all HIV-infected patients regardless of their clinical presentation. In contrast, significantly lower levels of IgG2 anti-gp41 were observed in patients at WR 5 and 6 (5%) when compared to those at stage WR 1 and 2 (88%). The IgG2 response to a recombinant gp 120/41 antigen, however, remained unchanged, suggesting that the lack of IgG2 response may be associated with lack of responsiveness to the carbohydrate epitope on gp41. Indeed, parallel measurements of IgG antibody responses to group A carbohydrate were also lower in patients at WR 5 and 6 stages, without affecting antibody responses to polyribosyl ribitol phosphate and phosphocholine. As antibody responses to group A carbohydrate with its N-acetyl D-glucosamine (GlcNAc) determinant were lower at the WR 5 and 6 stage of HIV disease, GlcNAc may be one of the antigenic determinants on gp41 that plays a critical role in some of the pathologic events of HIV infection.

Multiple levels of analysis of an IGHG4 gene deletion

Human immunoglobulin heavy chain constant region (IGHC) genes constitute a typical multigene family, usually comprising eleven genes on the telomere of chromosome 14 (14q32). In this region, deleted and duplicated haplotypes have been reported to exist with considerable frequency. Their origin is the result of either unequal crossing-over or looping out excision. In this paper, we report the characterization of a new type of deletion, involving the IGHG4 gene, in a subject who also carries a larger deletion of a previously described type on the second chromosome. Employment of several methods (polymerase chain reaction, standard Southern blot, pulsed field gel electrophoresis, serological techniques) to analyze these deleted haplotypes has resulted in a level of accuracy in their characterization that has not been achieved in previous cases. The site of recombination responsible for the IGHG4 deletion was restricted to a 2.5-kb region 3' of the G4 gene; this rules out any possible involvement of the S regions in the recombination process. The usefulness of the various techniques in the characterization of the deletions is also discussed, together with possible future applications in the field.

Identification of a nucleocapsid protein as a specific serological marker of human herpesvirus 6 infection

Enveloped whole virions and nucleocapsids of human herpesvirus 6 (HHV-6) strain Z29 were purified from supernatant fluids of infected human cord blood lymphocytes by filtration through polyvinylpyrrolidone-treated filters, banding on a Nycondenz step gradient, and centrifugation through two successive continuous sucrose gradients. More than 20 proteins ranging in molecular weight from less than 30,000 to more than 200,000 were identified in preparations of purified whole virions labeled with [35S]methionine and [35S]cysteine. Immunogenic virion proteins of HHV-6 were identified in immunoblot assays with human immune sera, immune sera generated from mice immunized with purified whole virions or purified nucleocapsids, and a monoclonal antibody generated from a mouse immunized with purified nucleocapsids. The sera and the monoclonal antibody reacted strongly with a 101-kilodalton protein in the immunoblots, suggesting that the protein is a component of the nucleocapsid. Human sera lacking HHV-6-specific antibodies and seropositive for one or more of the other human herpesviruses failed to react with this protein, indicating that it is a specific serologic marker for HHV-6 infection.

IgG heavy-chain subclass restriction of thyrotropin-binding inhibitory immunoglobulins in Graves' disease

The IgG subclass composition of antibodies is an important determinant of their function. Thyrotropin receptor antibodies cause the hyperthyroidism of Graves' disease but their subclass distribution has been incompletely investigated. We have therefore purified IgG subclasses from Graves' sera by passage over affinity columns designed to deplete all but a single subclass, and then assayed those pure subclass fractions for their ability to displace radiolabelled thyrotropin from its solubilized receptor as a measure of thyrotropin receptor antibody activity. Sufficient activity was recovered for analysis in nine of 10 Graves' patients, in five of whom activity was almost completely (97-100%) restricted to the IgG1 subclass; in the remaining four patients the response was predominantly IgG1 and IgG4 with marked under-representation of the IgG2 subclass. This contrasts with the unrestricted subclass response, in the same fractions, for autoantibodies against thyroglobulin and microsomes. These results suggest that there may be a primary defect at the B-cell level in Graves' disease.

Evaluation of immunotherapy-induced changes in specific IgE, IgG and IgG subclasses in birch pollen allergic patients by means of immunoblotting. Correlation with clinical response

Sera from 27 birch pollen-allergic patients who had undergone hyposensitization treatment for 22-41 months were studied by immunoblotting before and after therapy, whereby the levels of IgE, IgG and IgG1-4 antibodies directed against the major allergen Bet v I and minor allergens of birch pollen were monitored. The clinical benefit of immunotherapy (IT) was evaluated using a symptom specific questionnaire. In patients with good clinical response (responders, n = 18), as defined by improvement of symptoms, anti-Bet v I IgE antibodies were found to decrease in 10/18 patients (55.5%), whereas in 6/18 (33.3%) no change and in two cases (11.2%) an increase of specific IgE was observed. In the group of patients with unsatisfactory clinical outcome (non-responders, n = 9), 3/9 patients (33.3%) showed a decrease, 3/9 (33.3%) no change and 3/9 (33.3%) an increase in levels of IgE antibodies directed against Bet v I. In the case of minor allergens, 5/18 responders (27.7%) and 8/9 non-responders (88.8%) showed specific IgE before IT. In the responder group, no increase of specific IgE could be observed after IT. In non-responders, however, an increase of IgE directed against minor allergens was seen in 3/9 patients (33.3%). In all patients, regardless of therapeutical success, IT-induced elevated levels of specific IgG, IgG1 and in particular IgG4 directed against Bet v I were found. Regarding minor allergens, a heterogeneous pattern of IgG responses without significant correlation to clinical benefit was observed. Our results indicate that changes in IgG reactivity patterns against Bet v I and minor allergens, as shown by the immunoblot technique, did not correlate with good or bad clinical outcome.

Subclass distribution of IgG antibodies to the rat oesophagus stratum corneum (so-called anti-keratin antibodies) in rheumatoid arthritis

Serum IgG, labelling the stratum corneum of the rat oesophagus epithelium, so-called anti-keratin antibodies (AKA) constitute the most specific marker for the diagnosis of rheumatoid arthritis. In this study, we investigated 31 IgG AKA-positive rheumatoid sera and 21 control sera from patients with non-rheumatoid inflammatory rheumatic diseases. The serum level of IgG1,2,3 and 4 was determined by radial immunodiffusion and the subclass distribution of IgG AKA by a three-step semi-quantitative immunofluorescence assay using standard monoclonal antibodies specific for each of the four human IgG subclasses. In the rheumatoid sera, the serum level of IgG1 was found to be significantly increased and the level of IgG2 significantly decreased with regard to the control sera, while the levels of IgG3 and 4 as well as total IgG were in the normal range. IgG1,2,3, and 4 AKA were detected in 27 (87%), 6 (19%), 4 (13%) and 11 (35%) of the 31 rheumatoid sera, respectively, and were found to be independent of the clinical and biological indices of the disease. In spite of inter-individual heterogeneity, two predominant profiles were distinguished: IgG1 (alone) and IgG(1 + 4), which together represented 18 sera (58%). The large predominance of IgG1 AKA and the quasi-absence of IgG2 AKA suggest that the recognized antigen may be partly comprised of protein. Moreover, the high frequency of occurrence of IgG4 AKA might result from chronic exposure to the eliciting antigen, which could be a genuine autoantigen since we demonstrated that it is also present in the stratum corneum of human epidermis.

Immunoblot analysis of IgG subclasses of circulating antibodies in bullous pemphigoid

Sera from 20 patients with bullous pemphigoid (BP) were analyzed for the subclass distribution of IgG autoantibodies by Western immunoblotting of normal human heat-separated epidermal extracts. Strips were sequentially probed with patient sera, monoclonal antibodies (Mab) anti-human IgG1-4, and a labeled anti-mouse Ig. The relative dilutions of each subclass-specific Mab were determined in dot immunobinding experiments in order to give uniform reactivity to the corresponding human IgG subclass. Circulating BP autoantibodies reacting with the major BP antigen of 220 kDa and/or a 165-kDa band showed a stricking predominance of IgG4. Overall, IgG4 was the major subclass reactive with the 220-kDa band, whereas, in addition to IgG4, IgG1 and IgG2 were frequently represented in the response to the 165-kDa band. Complement fixation of circulating BP antibodies was studied by complement indirect immunofluorescence using human serum as source of complement and FITC goat anti-human C3, C1q, and C4, on normal human skin substrate. When circulating BP antibodies contained IgG1 or IgG2 in addition to IgG4, they fixed C3 and, in some cases, C1q and C4, suggesting complement activation by either the classical or the alternate pathway.

Toxoplasma antigens recognized by immunoglobulin G subclasses during acute and chronic infection

The immunoglobulin G (IgG) subclass response to Toxoplasma gondii antigens during the acute and chronic stages of T. gondii infection were studied by using immunoblots with reduced antigen (RA) and nonreduced antigen (NRA) preparations. Serum samples were from individuals with acute or chronic T. gondii infection, and sequential samples were from women who seroconverted during gestation and were treated with spiramycin. IgG1 antibodies were predominant in sera from each of the groups and recognized a large number of RA and NRA. In the latter group of patients, IgG1 and IgG3 were the first antibodies to appear in response to the infection. In all groups, an antigen with a molecular weight (MW) of 30,000 was the most intensely stained and frequently recognized by IgG1 antibodies in NRA preparations. In RA preparations, antigens of MW 35,000 and 30,000 were the most intensely stained and frequently recognized by IgG1 antibodies. An antigen with an MW of 22,000 was intensely stained in the IgG1 immunoblots of the NRA preparation and to a lesser extent in the RA preparation. In contrast to immunoblots with IgG1 antibodies, very few antigens in the RA and NRA preparations were detected by IgG2 and IgG3 antibodies; IgG4 antibodies rarely detected any antigens. Of interest was that IgG2 antibodies detected antigens distributed over the entire MW range, whereas those detected by IgG3 antibodies were located mostly below the 35,000 MW marker. Enzyme-linked immunosorbent assay results paralleled those of the immunoblots in that IgG1 antibodies were predominant.

Affinity purification of IgG subclasses and the distribution of thyroid auto-antibody reactivity in Hashimoto's thyroiditis

To delineate accurately the IgG subclass distribution of thyroid auto-antibodies, sera from nine patients with Hashimoto's thyroiditis were fractionated into IgG subclasses by complete depletion of the other IgG subclasses on affinity columns. All IgG subclass fractions contained thyroglobulin and microsomal (or thyroid peroxidase) antibody activity, although when compared to the total serum concentrations of IgG subclasses, IgG4 antibodies were overrepresented. However, in contrast to recent studies, this particular subclass never predominated--IgG4 antibody levels being exceeded by those of the IgG1 and IgG2 subclasses; it seems likely that these differences relate to varying sensitivity for different subclasses in previously used assay methods. This pattern of subclass activity differed from that of tetanus toxoid antibodies, which were found in six subjects. There was no light chain restriction within any subclass, showing that the overproduction of IgG4 thyroid antibodies is not of monoclonal origin. The functional affinity of subclasses for both thyroid antigens varied between patients, but IgG2 subclass fractions showed the highest functional affinity in the majority of samples. We also found that IgG2 subclass thyroid antibodies were ineffective in eliciting antibody-dependent cell-mediated cytotoxicity, as distinct from the other three subclasses. Our results show that thyroid antibodies are less restricted in their IgG subclass distribution and patients are less heterogeneous than previously described. Moreover, IgG2 thyroid antibodies are quantitatively important and differ in relative functional affinity and effector function from IgG1 and IgG4 thyroid antibodies.

Evaluation of production and characterization of monoclonal antibodies to human IgG of four subclasses

Human IgG of four subclasses, semi-purified from pooled human serum by a series of DEAE ion exchange and protein A affinity chromatographies, were used as immunogens and initial screening antigens to produce subclass-specific and -restricted monoclonal antibodies (McAbs). These McAbs were bound to CNBr-activated Sepharose 4B and utilized in immunoaffinity chromatography to prepare four polyclonal human IgG subclasses of satisfactory purities, which were then used as final screening antigens. Subclass-specific McAbs thus chosen were further evaluated for subclass- and especially allotype-specificity using a panel of monoclonal IgG myeloma proteins with representative Gm markers for each subclass in micro enzyme-linked immunosorbent assay (ELISA). A total of 10 clones of subclass-specific McAbs (one for anti-IgG1, three anti-IgG2, two anti-IgG3, four anti-IgG4) were established. Among them, IgG2-specific clones of HG2-30F and HG2-56F, IgG3-specific HG3-7C and HG3-32C, and IgG4-specific HG4-53G McAbs were superior to the corresponding specificity standard McAbs chosen by the Human Immunoglobulins Subcommittee of the WHO/International Union of Immunological Societies (IUIS) in 1985. As allotype-specific McAbs, HG1-1E for G1m(az) and HG3-3B for G3m(b) were obtained. In micro ELISA of this study as well as all protocols of the previous WHO/IUIS collaborative study, antigens (myeloma IgG subclasses) were immobilized or fixed to a solid phase, resulting in possible variations in their epitope expressions. We developed a new assay system, micro radioimmunoassay (RIA), in which reactivities of McAbs against free IgG subclasses in solution can be evaluated. HG2-30F, having extremely high reactivities to coated IgG2 in micro ELISA, remarkably reduced its reactivities to free IgG2 in solution in micro RIA. Two other clones also showed some different reactivities in micro RIA and micro ELISA. We believe that this micro RIA is valuable for evaluation of McAbs reactivities against native human IgG subclasses in solution.

Immunogenicity of Haemophilus influenzae type b polysaccharide-outer membrane protein conjugate vaccine in patients who acquired Haemophilus disease despite previous vaccination with type b polysaccharide vaccine

To investigate the basis of the immune defect in children who acquire invasive Haemophilus disease despite previous vaccination with Haemophilus influenzae type b (Hib) polysaccharide vaccine, we determined the ability of vaccine failure patients with low levels of serum anticapsular antibody (less than 1 microgram/ml) to respond to reimmunization. Thirty-four patients, ranging in age from 27 to 61 months, were vaccinated with either Hib polysaccharide (n = 20) or Hib polysaccharide-outer membrane protein conjugate vaccine (n = 14). All but three of the children had normal serum concentrations of immunoglobulins, including IgG2. The geometric mean serum anticapsular antibody concentration of the group given polysaccharide vaccine increased from 0.27 microgram/ml before vaccination to 0.65 microgram/ml 1 month later (p less than 0.05), but the magnitude of the response was nearly 10-fold less than that of 31 age-matched control children given polysaccharide vaccine (6.3 micrograms/ml, p less than 0.001). In contrast, all 14 patients with vaccine failure who were given conjugate vaccine showed increases of fivefold or more in serum anticapsular antibody (geometric means 0.35 and 12.8 micrograms/ml, respectively; p less than 0.001). All patients with vaccine failure who did not respond to polysaccharide vaccine were subsequently given conjugate vaccine, and all had high antibody responses. Most patients tested showed increases in complement-mediated serum bactericidal activity. These data suggest that immunization with conjugate vaccine confers protection against Hib disease to children who, because of genetic or other reasons, cannot respond to the unconjugated form of the polysaccharide vaccine.

Glomerular and serum immunoglobulin G subclasses in IgA nephropathy

The distribution of human IgG subclasses among mesangial glomerular deposits of 11 patients with IgA nephropathy (IgA-N) was examined by indirect immunofluorescence with subclass-specific mouse monoclonal antibodies (mAb). A subclass restriction was observed with mesangial deposits containing almost exclusively IgG1 (81% of the studied biopsies) and IgG3 (64%). IgG2 was present in only 1 out of the 11 cases studied and IgG4 was never found to be present, although seven different anti-IgG4 mAb were used. In addition, serum levels of total IgA and IgG, as well as serum IgG subclass levels, were measured in 27 patients with IgA nephropathy by an indirect competitive immunoenzymatic assay using mAb. It was noted in IgA-N patients, but not in normal individuals, that there was significant positive correlation between total IgA and IgG serum levels which was entirely due to a positive correlation between total serum IgA and IgG2 levels. This study provides no explanation for the subclass restrictions observed but suggests that (i) the presence of IgA-IgG1-IgG3 in mesangial deposits may be secondary to an antigenic stimulation, possibly viral, and (ii) the positive correlation between IgA and IgG2 serum levels may result from an increased T helper function.