Determination of the functional affinity of IgG1 and IgG4 antibodies to tetanus toxoid by isotype-specific solid-phase assays

Characterization of genetic predisposition and autoantibody profile in atypical haemolytic-uraemic syndrome

We previously reported that Indian paediatric patients with atypical haemolytic-uraemic syndrome (aHUS) showed high frequencies of anti-complement factor H (FH) autoantibodies that are correlated with homozygous deletion of the genes for FH-related proteins 1 and 3 (FHR1 and FHR3) (FHR1/3-/- ). We now report that Indian paediatric aHUS patients without anti-FH autoantibodies also showed modestly higher frequencies of the FHR1/3-/- genotype. Further, when we characterized epitope specificities and binding avidities of anti-FH autoantibodies in aHUS patients, most anti-FH autoantibodies were directed towards the FH cell-surface anchoring polyanionic binding site-containing C-terminal short conservative regions (SCRs) 17-20 with higher binding avidities than for native FH. FH SCR17-20-binding anti-FH autoantibodies also bound the other cell-surface anchoring polyanionic binding site-containing region FH SCR5-8, at lower binding avidities. Anti-FH autoantibody avidities correlated with antibody titres. These anti-FH autoantibody characteristics did not differ between aHUS patients with or without the FHR1/3-/- genotype. Our data suggest a complex matrix of interactions between FHR1-FHR3 deletion, immunomodulation and anti-FH autoantibodies in the aetiopathogenesis of aHUS.

Detection of ovomucoid-specific low-affinity IgE in infants and its relationship to eczema

BACKGROUND

Allergen-specific low-affinity IgE was previously detected in cord blood by a highly sensitive densely carboxylated protein (DCP) chip, but not by ImmunoCAP. Here, we investigated the presence of low-affinity IgE during the early life of infants and observed its relationship with eczema.

METHODS

We conducted a birth cohort study, collecting sera at birth and 6 and 14 months of age (n = 110). We monitored the ovomucoid (OM)- and egg white (EW)-specific IgE (sIgE) by ImmunoCAP or DCP chip and analyzed the antigen affinity of sIgE by binding inhibition assays in the presence or absence of a mild chaotropic agent, diethyl amine (DEA). The low- and high-affinity OM-sIgEs and sensitization risk factors were analyzed by a multivariate logistic analysis.

RESULTS

The OM-sIgE measured by DCP chip significantly correlated with that measured by ImmunoCAP, but some samples assessed as OM-sIgE positive by DCP chip were considered OM-sIgE negative by ImmunoCAP. Binding inhibition analysis after DEA treatment was performed for participants judged as OM-sIgE positive by DCP chip at 14 M. The group assessed as negative for OM- and EW-sIgE by ImmunoCAP at 6 and 14 months showed a larger binding inhibition curve shift after DEA treatment than did the group assessed as positive at these times, indicating the presence of low-affinity sIgE antibodies at 14 months. The logistic regression analysis found that persistent eczema from 6 to 14 months is a significant risk factor for developing high-affinity, but not low-affinity, sIgE.

CONCLUSIONS

Human infant peripheral blood contains allergen-specific low-affinity sIgE. Persistent eczema is related to the development of high-affinity, but not low-affinity, IgE.

A simple nonradioactive method for the determination of the binding affinities of antibodies induced by hapten bioconjugates for drugs of abuse

The accurate analytical measurement of binding affinities of polyclonal antibody in sera to heroin, 6-acetylmorphine (6-AM), and morphine has been a challenging task. A simple nonradioactive method that uses deuterium-labeled drug tracers and equilibrium dialysis (ED) combined with ultra performance liquid chromatography/tandem mass spectrometry (UPLC/MS/MS) to measure the apparent dissociation constant (K d) of antibodies to 6-AM and morphine is described. The method can readily detect antibodies with K d in the low nanomolar range. Since heroin is rapidly degraded in sera, esterase inhibitors were included in the assay, greatly reducing heroin hydrolysis. MS/MS detection directly measured the heroin in the assay after overnight ED, thereby allowing the quantitation of % bound heroin in lieu of K d as an alternative measurement to assess heroin binding to polyclonal antibody sera. This is the first report that utilizes a solution-based assay to quantify heroin-antibody binding without being confounded by the presence of 6-AM and morphine and to measure K d of polyclonal antibody to 6-AM. Hapten surrogates 6-AcMorHap, 6-PrOxyHap, MorHap, DiAmHap, and DiPrOxyHap coupled to tetanus toxoid (TT) were used to generate high affinity antibodies to heroin, 6-AM, and morphine. In comparison to competition ED-UPLC/MS/MS which gave K d values in the nanomolar range, the commonly used competition enzyme-linked immunosorbent assay (ELISA) measured the 50% inhibition concentration (IC50) values in the micromolar range. Despite the differences in K d and IC50 values, similar trends in affinities of hapten antibodies to heroin, 6-AM, and morphine were observed by both methods. Competition ED-UPLC/MS/MS revealed that among the five TT-hapten bioconjugates, TT-6-AcMorHap and TT-6-PrOxyHap induced antibodies that bound heroin, 6-AM, and morphine. In contrast, TT-MorHap induced antibodies that poorly bound heroin, while TT-DiAmHap and TT-DiPrOxyHap induced antibodies either did not bind or poorly bound to heroin, 6-AM, and morphine. This simple and nonradioactive method can be extended to other platforms, such as oxycodone, cocaine, nicotine, and methamphetamine for the selection of the lead hapten design during substance abuse vaccine development.

Assessment of IgG avidity against pertussis toxin and filamentous hemagglutinin via an adapted enzyme-linked immunosorbent assay (ELISA) using ammonium thiocyanate

Antibody avidity, defined as the strength of binding between antibody and antigen, represents a functional measure of affinity maturation of antibodies. Determination of the antibody avidity is usually performed separating high and low avidity antibodies by dissociating agents, but measurement of the antibody avidity in humans is rather complicated, due to the heterogeneity of the antibodies produced in response to complex antigens, e.g. after vaccinations. The purpose of the present study was to evaluate the experimental determinants of the assessment of avidities of IgG antibodies directed against pertussis toxin (IgG-anti-PT) and filamentous hemagglutinin (IgG-anti-FHA) produced after pertussis vaccination using an adapted ELISA and ammonium thiocyanate (NH(4)SCN) as dissociating agent. Our experiments revealed that the results of avidity testing depend very much on experimental conditions and may over- or underestimate the relative avidity of IgG-anti-PT and IgG-anti-FHA antibodies. Whereas in our findings avidity seems to be independent from the initial antibody concentration in a wide range of measures, RAI depends on NH(4)SCN concentration, time of incubation and temperature of the reaction. The presented method allows an accurate measurement of the IgG antibody avidity against both Bordetella pertussis antigens PT and FHA, using NH(4)SCN as chaotropic agent in concentrations lower than 3.0M for 20 min time of incubation at 37 °C. Different experimental conditions in testing pertussis-specific IgG antibody avidity should be considered in interpretation and comparability of data of different studies.

Origin and anti-tumor effects of anti-dsDNA autoantibodies in cancer patients and tumor-bearing mice

In the present investigation, we detected anti-dsDNA autoantibodies in cancer patients and modeled the production of anti-dsDNA autoantibodies by inoculating tumors in BALB/c mice. Moreover, induction of anti-dsDNA autoantibodies by immunization with inactivated tumor cells and their DNA indicated that DNA of tumor cells was probably the primary antigen, which was supported by the significantly increasing levels of sera free DNA in cancer patients and tumor-bearing mice. cELISA and indirect immunofluorescence assay showed that the anti-dsDNA autoantibodies could bind to the surface components of tumor cells. In vitro assay showed that immunosera at week 6 from immunized mice displayed significant cytotoxicity to tumor cells compared to that of negative control, but no cytotoxicity mediated by immunosera at week 22 was observed. In addition, by flow cytometry and electrophoresis of fragmented DNA, the cytotoxicity might probably be mediated by apoptosis. Our data also showed that the ability of the anti-dsDNA autoantibodies to induce apoptosis of SP2/0 and Wehi 164 cells was significantly correlated (r = 0.990, p < 0.01 and r = 0.901, p < 0.05) with their functional affinity. In vivo, the growth of solid tumors was significantly inhibited in the immunized mice inoculated directly with SP2/0 and Wehi 164 cells, or in the naïve mice which were inoculated with SP2/0 cells preincubated with immunosera containing anti-dsDNA autoantibodies. In conclusion, we demonstrated the origin of anti-dsDNA autoantibodies in cancer patients and tumor-bearing mice. And our data also showed that these autoantibodies revealed anti-tumor effect by inducing apoptosis.

Absence of avidity maturation of autoantibodies to the protein tyrosine phosphatase-like IA-2 molecule and glutamic acid decarboxylase (GAD65) during progression to type 1 diabetes

Immunoglobulin G avidity assays are used to distinguish between the acute and chronic phase of several infectious diseases, and there is evidence of autoantibody affinity maturation also in autoimmune diseases. To assess whether the analysis of the avidity of autoantibodies against the protein tyrosine phosphatase-like IA-2 molecule and glutamic acid decarboxylase (GAD65) could improve the accuracy of risk assessment of progression to clinical type 1 diabetes, we established methods for the determination of the autoantibody avidity based on our previously developed time-resolved fluorometric IA-2 and GAD65 autoantibody (IA-2A and GADA) assays. The avidity indices of sequential plasma samples from six IA-2A-positive and seven GADA-positive prediabetic children were analysed applying elution with urea and diethylamine (DEA). For comparison, corresponding avidity indices of control children, who have remained non-diabetic for at least 3 years after seroconversion to IA-2A and GADA positivity, were analysed. For most of the children, only a slight fluctuation in the avidity index values was observed over time, although the titres for IA-2A and GADA varied substantially in some cases. The avidity indices of the prediabetic children remained within the same range as those of the control group throughout the follow-up. Our results indicate that the analysis of the avidity index levels of IA-2A and GADA does not improve the accuracy of the prediction of type 1 diabetes based on autoantibody detection.

A new method for determination of varicella-zoster virus immunoglobulin G avidity in serum and cerebrospinal fluid

Background

Avidity determination of antigen-specific immunoglobulin G (IgG) antibodies is an established serological method to differentiate acute from past infections. In order to compare the avidity of varicella-zoster virus (VZV) IgG in pairs of serum and cerebrospinal fluid (CSF) samples, we developed a new technique of avidity testing, the results of which are not influenced by the concentration of specific IgG.

Methods

The modifications introduced for the new VZV IgG avidity method included the use of urea hydrogen peroxide as denaturing reagent, the adaptation of the assay parameters in order to increase the sensitivity for the detection of low-level VZV IgG in CSF, and the use of a new calculation method for avidity results. The calculation method is based on the observation that the relationship between the absorbance values of the enzyme immunoassays with and without denaturing washing step is linear. From this relationship, a virtual absorbance ratio can be calculated. To evaluate the new method, a panel of serum samples from patients with acute and past VZV infection was tested as well as pairs of serum and CSF.

Results

For the serum panel, avidity determination with the modified assay gave results comparable to standard avidity methods. Based on the coefficient of variation, the new calculation method was superior to established methods of avidity calculation.

Conclusions

The new avidity method permits a meaningful comparison of VZV IgG avidity in serum and CSF and should be of general applicability for easy determination of avidity results, which are not affected by the concentration of specific IgG.

The protective efficacy of MSP4/5 against lethal Plasmodium chabaudi adami challenge is dependent on the type of DNA vaccine vector and vaccination protocol

The enhancement of immunogenicity of malarial DNA vaccines is important if they are to have practical application in protecting against blood-stage malaria. Here we describe three different DNA vaccine vector types used in conjunction with the blood-stage merozoite surface protein 4/5 (MSP4/5), the murine homologue of Plasmodium falciparum MSP4 and MSP5, in an attempt to enhance survival against lethal Plasmodium chabaudi adami DS blood-stage challenge. MSP4/5 was inserted into VR1020 (secretory), monocyte-chemotactic protein-3 (MCP-3) (chemoattractant), and cytotoxic T-lymphocyte antigen 4 (CTLA4) (lymph node targeting) vectors. Mice were immunized intradermally via gene-gun, IM injection, or boosting with recombinant MSP4/5 protein. Antibody responses after boosting were predominantly of the IgG1 and IgE isotypes, with low avidity antibodies produced in DNA primed groups. Despite antibody responses comparable to recombinant protein immunization, boosting mice primed with antigens encoded by MCP-3 and CTLA4 vectors did not enhance survival compared to vector control groups. Gene-gun vaccination using VR1020/MSP4/5 followed by recombinant MSP4/5 boosting, or gene-gun DNA vaccination alone using MCP-3/MSP4/5, resulted in enhanced survival compared to empty vector control mice. The results suggest that the enhancement of survival against lethal blood-stage malaria challenge after utilizing MSP4/5 DNA vaccination is therefore highly dependent on the route and type of vaccine vector employed.

Naked DNA when co-administered intranasally with heat-labile enterotoxin of Escherichia coli primes effectively for systemic B- and T-cell responses to the encoded antigen

In this study a novel prime-boost immunisation strategy was evaluated. Priming of BALB/c mice by the intranasal route with plasmid DNA encoding beta-galactosidase (LacZ) with or without heat-labile enterotoxin (LT) of Escherichia coli as a mucosal adjuvant, resulted in the induction of weak serum antibody and proliferative T-cell responses. However, following an intraperitoneal booster injection with the beta-galactosidase protein (beta-gal), strong antibody and proliferative T-cell responses were induced in all the mice. These responses were highest in mice primed intranasally with a mixture of LacZ+LT as compared to those mice primed with DNA (LacZ) or protein (beta-gal) alone. Moreover, LacZ+LT primed mice produced high avidity antibodies and the subclasses of serum antibodies were IgG1 and IgG2a, suggesting a mixed Th1/Th2-type response. Priming of mice with either protein (beta-gal) or DNA (LacZ) alone, produced predominantly IgG1 antibodies, suggesting a Th2-type response. These findings suggest that the use of a heterologous DNA-prime, protein-boost immunisation scheme combining different routes of administration, might be an advantageous strategy for the induction of accelerated immune responses.

Early effect of ultrarush venom immunotherapy on the IgG antibody response

BACKGROUND

We have previously shown in several allergy models that allergic and tolerance status with respect to allergens is associated with a somewhat different dominant specificity of IgG antibodies. The objective was to test this hypothesis in the compelling model of ultrarush venom immunotherapy (VIT), which induces clinical tolerance after only a few hours of treatment.

METHODS

Antibody titers and specificity were evaluated through solid-phase ELISA using streptavidin-biotin technology in 12 patients allergic to wasp venom before and during the ultrarush procedure (at 12 h, 24 h, and 15 days). The results were compared with those from another group of 20 patients treated with venom injections for at least 2 years.

RESULTS

No significant change was observed in IgG titers during the early phase of VIT. The capacity of individual sera to prevent the antigen binding of pooled IgG from allergic patients changed rapidly, with mean percentage inhibitions falling from 80+/-15%, before starting VIT, to 26+/-14%, 35+/-15%, and 34+/-5% after 12 h, 24 h, and 15 days of treatment, respectively (P<0.001 by one-way ANOVA). The capacity of individual sera to prevent the antigen binding of pooled IgG from patients receiving prolonged VIT changed, with mean percent inhibitions increasing from 47+/-8%, before starting VIT, to 76+/-7%, 83+/-6%, and 87+/-6% after 12 h, 24 h, and 15 days of treatment, respectively (P<0.001 by one-way ANOVA).

CONCLUSIONS

During the initial phase of ultrarush VIT, a change in IgG specificity, i.e., a change in the set of epitopes dominantly recognized by IgG on wasp-venom antigens, occurred concomitantly with early clinical tolerance and was already detectable a few hours after the onset of treatment. Although it may be an epiphenomenon, this change represents the earliest humoral modification described so far during this procedure. The mechanism is unknown, but it appears to be a selective depletion of the highest avidity antibody fraction by the venom injected in large doses at this stage of therapy. Finally, our data now show the previously documented association between a particular IgG specificity and the clinical status (allergy vs tolerance) to be true also with ultrarush VIT, a model in which the clinical ability to display allergic symptoms is rapidly reversed.

Screening of protective antigens of Japanese encephalitis virus by DNA immunization: a comparative study with conventional viral vaccines

In this study, we evaluated the relative role of the structural and nonstructural proteins of the Japanese encephalitis virus (JEV) in inducing protective immunities and compared the results with those induced by the inactivated JEV vaccine. Several inbred and outbred mouse strains immunized with a plasmid (pE) encoding the JEV envelope protein elicited a high level of protection against a lethal JEV challenge similar to that achieved by the inactivated vaccine, whereas all the other genes tested, including those encoding the capsid protein and the nonstructural proteins NS1-2A, NS3, and NS5, were ineffective. Moreover, plasmid pE delivered by intramuscular or gene gun injections produced much stronger and longer-lasting JEV envelope-specific antibody responses than immunization of mice with the inactivated JEV vaccine did. Interestingly, intramuscular immunization of plasmid pE generated high-avidity antienvelope antibodies predominated by the immunoglobulin G2a (IgG2a) isotype similar to a sublethal live virus immunization, while gene gun DNA immunization and inactivated JEV vaccination produced antienvelope antibodies of significantly lower avidity accompanied by a higher IgG1-to-IgG2a ratio. Taken together, these results demonstrate that the JEV envelope protein represents the most critical antigen in providing protective immunity.

Urinary loss of immunoglobulin G anti-F(ab)2 and anti-DNA antibody in systemic lupus erythematosus nephritis

The objective of this study was to determine whether the low levels of serum immunoglobulin G (IgG) anti-F(ab)2 seen in some patients with active systemic lupus erythematosus (SLE) were directly related to the deposition of antibody with this specificity in the kidney or alternatively to the urinary loss of IgG anti-F(ab)2. Serum Levels of IgG anti-F(ab)2, anti-tetanus toxoid, and anti-ds DNA antibody were measured in parallel with urinary excretion of these same 3 antibodies in 28 patients with SLE nephritis and in 28 control patients with other forms of chronic kidney disease. Low levels of both serum IgG anti-F(ab)2 or anti-tetanus antibody appeared to correlate with increased levels of urinary loss of these same antibodies in some patients with SLE and in control subjects with kidney disease. However, urinary loss could not account for low serum levels of either IgG antibody in many subjects. Quantitative 24-hour urinary losses of IgG anti-F(ab)2 and anti-DNA were much higher in patients with SLE than in control subjects with kidney disease (P < .05), whereas amounts of IgG urinary loss of anti-tetanus were similar in patients with SLE and in control subjects. In nearly 1 third of SLE nephritis patients, 13% to 53% of total excreted urinary IgG showed anti-DNA enzyme-linked-immunosorbent assay reactivity. Urinary IgG in many patients with SLE showed both anti-DNA and anti-F(ab)2 reactivity, but dual anti-DNA/F(ab)2 specificity was more pronounced in affinity-isolated serum IgG anti-DNA or anti-F(ab)2 than in excreted urinary IgG molecules. The affinity of urinary IgG for either DNA or F(ab)2 was much lower than the same antibody activities measured either in serum or in kidney biopsy eluates. When the relative affinity of anti-DNA antibody in serum, urine, and kidney biopsy eluate was measured in parallel, the highest affinity antibody was found in kidney biopsy eluates, followed by serum antibody with urine antibody affinity showing the lowest values. These findings suggest a relative concentration of the highest affinity, doubly reactive IgG anti-DNA/F(ab)2 in SLE kidney tissues during SLE nephritis and implicate this process as an important factor in ongoing tissue damage.

Heterogeneity in the occurrence of a subset of autoantibodies to glutamic acid decarboxylase in autoimmune polyendocrine patients with islet cell antibodies

Glutamic acid decarboxylase-65 (GAD-65) is a major target for autoantibodies and autoreactive T cells in patients with insulin-dependent diabetes mellitus (IDDM). Autoantibodies to GAD are also found in patients with stiff man syndrome (SMS) or polyendocrine autoimmunity (PE). The epitope specificities of autoantibodies to GAD in IDDM and SMS have been well documented, but the locations of autoantibody epitopes of GAD in PE patients have not been mapped. Thus, the properties of anti-GAD antibodies in PE patients (with or without diabetes) were investigated. The ability of PE serum antibodies to inhibit the binding of the mouse monoclonal antibody, GAD-6, to native GAD in ELISA was determined. For PE patients without diabetes, levels of inhibition of GAD-6 binding ranged from 0% to almost 70% and were unrelated to the level of binding of serum antibodies to GAD (P = 0.351) or to the functional affinities of these antibodies. This suggests differences in the epitope specificities of anti-GAD antibodies in different patients. Levels of inhibition were also unrelated to clinical condition. SMS antibodies showed similar levels of inhibition of GAD-6 binding. Similar analysis was applied to PE patients with diabetes and levels of inhibition of GAD-6 binding to GAD were determined. These ranged from 0% to 80%, and levels of inhibition were similar in samples taken before or after diabetes onset. There was no significant difference between anti-GAD antibodies from PE patients with or without diabetes in the range of abilities to inhibit GAD-6 binding to GAD, although the highest levels of inhibition were given by sera from non-diabetic patients. This raises the possibility of differential expression of subsets of anti-GAD antibodies in progressive versus slow or non-progressive anti-islet autoimmune responses. Serum antibodies of PE and SMS patients did not inhibit the binding of antibodies specific for the extreme C-terminus of GAD, indicating that this is not the site of the epitopes for the patients' antibodies or for GAD-6.

Genetic, structural and functional properties of an IgG DNA-binding monoclonal antibody from a lupus patient with nephritis

Antibodies binding to double-stranded (ds) DNA are strongly associated with renal involvement in patients with systemic lupus erythematosus (SLE). We have generated two new IgG DNA-binding monoclonal antibodies (mAb), RH-14 and DIL-6, from the peripheral blood lymphocytes of two SLE patients with glomerulonephritis using the heteromyeloma cell line CB-F7. RH-14 is an IgG1 lambda antibody which also bound to single-stranded DNA, histones and nucleosomes. DIL-6 is an IgG3 lambda antibody with restricted antigen binding specificity. cDNA encoding the variable regions of the heavy (V(H)) and light (V(L)) chains of RH-14 was sequenced and the antigen binding site of this mAb was computer modelled. Sequence analysis of V(H) and V(L) regions of RH-14 showed that V(H) is derived from germ-line gene V3-7, a member of the V(H)3 family, and V(L) is derived from DPL 11, a member of the V(lambda)2 family. Somatic mutations and basic amino acid residues are identified in the complementarity-determining regions of both V(H) and V(L) regions. The nephritogenic properties of these mAb were analyzed by implanting and growing the hybridoma cells secreting the mAb in the peritoneum of SCID mice. The animals that received the RH-14 hybridoma produced higher levels of proteinuria (3 to > or = 4) (p < 0.001) compared to the groups that received DIL-6 (trace to > or = 1) or CB-F7 (trace). Electron microscopy of kidney sections from all the RH-14-implanted animals showed granular immunoglobulin deposition in the renal glomerular capillaries and mesangium. In this study we have shown for the first time using electron microscopy that a human IgG anti-dsDNA mAb, RH-14, is nephritogenic and that deposition of such an antibody alone is sufficient to induce renal damage.

DNA immunization: induction of higher avidity antibody and effect of route on T cell cytotoxicity

Immunizations of mice with plasmid DNAs encoding ovalbumin (OVA), human Ig, and hen egg lysozyme were compared with doses of soluble protein (without adjuvant) that induced similar IgG responses. The route of immunization influenced the magnitude of the antibody (Ab) response in that intradermal (i.d.) injection elicited higher IgG Ab levels than i.m. injection in both DNA- and protein-immunized mice. Although total IgG levels were similar to soluble protein controls, the avidity of the anti-OVA Abs generated by DNA immunization were 100- and 1,000-fold higher via the i.m. or i.d. route, respectively. However, despite the generation of high-avidity Ab in DNA-immunized mice, germinal centers could not be detected in either DNA- or protein-immunized mice. Examination of the IgG subclass response showed that IgG2a was induced by i.m. DNA immunization, coinciding with elevated interferon gamma production, whereas a dominant and elevated IgG1 response, coinciding with detectable interleukin 4 production, was generated after i.d. immunization with DNA or soluble OVA and hen egg lysozyme but not human Ig protein. As expected, cytotoxic T cell (CTL) responses could be detected only after DNA immunization. I.d. immunization produced the strongest CTL responses early (2 weeks) but was similar to i.m. later. Therefore, DNA immunization can differ from protein immunization by its ability to induce rapid CTL responses and higher avidity Ab, both of which are advantageous for vaccination.

Affinity columns containing anti-DNA Id+ human myeloma proteins adsorb human epibodies from intravenous gamma globulin

OBJECTIVE

To study eluates of intravenous gamma globulin (IVGG) prepared from affinity columns of human cationic IgG myeloma proteins bearing anti-DNA idiotype (Id) markers 16/6, F4, 3I, and 8.12 for possible anti-Id (combining site) blocking activity.

METHODS

Anti-DNA idiotypic antibody activity was studied in 3 preparations of IVGG containing high, medium, and low levels of IgG anti-F(ab')2, and in 4 other commercial IVGG preparations. Affinity-purified IgG anti-DNA (APAD) from systemic lupus erythematosus (SLE) patients was biotinylated, and binding to DNA coated on enzyme-linked immunosorbent assay plates was used to measure anti-DNA antibody activity. IVGG was adsorbed to Sepharose 4B affinity columns linked to a panel of cationic human IgG myeloma proteins positive for anti-DNA Id markers 16/6, F4, 3I, and 8.12. Material adsorbing to such columns was eluted at low pH (2.5) and after neutralization, tested for its ability to inhibit biotinylated APAD reacting with DNA.

RESULTS

Only 0.05-0.9% of IVGGs bound firmly to Id affinity columns. These IVGGs were then eluted, using pH 2.5 glycine-saline and eluates neutralized to pH 7.4. Column flowthrough and eluate fractions were compared for their ability to block SLE APAD reacting with DNA. Significant inhibition of SLE APAD combining sites was observed with eluates from anti-DNA Id affinity columns; however, no correlation between IVGG anti-F(ab')2 activity and true anti-Id blocking of APAD was apparent. No residual anti-Id activity remained in column flowthrough fractions. No anti-Id blocking activity was recorded for IVGG eluates from human cationic myeloma columns devoid of the 4 anti-DNA Id markers. DNase treatment of IVGG or Id column eluates did not affect anti-Id blocking activity. Thus, all detectable anti-DNA idiotypic antibody capable of blocking SLE anti-DNA combining sites bound to Id+ affinity columns. Column eluates also showed some relative concentration of IgG anti-DNA activity, which was of lower affinity for DNA than antibodies also present in eluates which blocked anti-DNA combining sites.

CONCLUSION

The presence of both anti-DNA and antiidiotypic (anti-combining site) activity in human anti-DNA Id column eluates indicates that epibodies from IVGG are relatively concentrated when this strategy is used. This approach may lead to a new strategy for treatment of SLE nephritis.

Immunoreactivity of a new generation of horse F(ab')2 preparations against European viper venoms and the tetanus toxin

The immunoreactivity of the current and the new more purified, pasteurized preparations of horse F(ab')2 against the tetanus toxin and Vipera aspis venom was investigated with a biosensor based on technology using the optical phenomenon of surface plasmon resonance. Immunoreactivity data were compared with seroneutralization titres to investigate immunoreactivity-immunoprotection efficacy relationships. The association-dissociation rate and affinity constants of the current and the new tetanus toxin-specific F(ab')2 preparations were similar, at about 10(4) M-1 sec-1, 10(-4) sec-1 and 10(8) M-1, respectively. Similar values were found using a solid immunoradiometric assay. To assess the immunoreactivity of V. aspis venom-specific horse F(ab')2, the mol. wt and percentage of the antigenic fractions of V. aspis venom were determined. Western blotting of electrophoresis gels showed four antigenic fractions of V. aspis venom (mol. wts 17,500, 28,500, 32,000 and 60,000), which represented 6, 3.4, 17.7 and 5% of total venom, respectively. Association and dissociation rate constants were in the same range as those of the tetanus toxin-F(ab')2 interactions for each of the four antigenic fractions. Seroneutralization of both tetanus toxin and V. aspis by the corresponding specific F(ab')2 showed that the LD50 mg-1 protein was 1.76-fold and 1.51-fold higher with the new than with the current preparations, respectively. These improvements in efficacy were in close agreement with the higher immunoreactive fraction ratios, which were 2-fold and 1.8-fold higher with the new preparations. These results demonstrate that the removal of non-IgGT immunoglobulins and the pasteurization treatment have no overall influence on F(ab')2 affinity but improve the specific activity of these new antitoxin horse F(ab')2.

Relative functional affinity of specific anti-core IgG in different categories of hepatitis B virus infection

While resolution of hepatitis B virus (HBV) infection occurs in most cases, a carrier state can exist in which the HBV surface antigen (HBsAg) persists. Some carriers are also positive for the HBV "e" antigen (HBeAg), indicative of high viral replication. Others are HBV "e" antibody (anti-HBe)-positive carriers in whom there appears to be a fall in the level of viral replication with the appearance of antibodies against the "e" antigen. The former group of carrier is considered to be at a higher risk of transmitting HBV infection than the latter. In order that a carrier state may occur, some degree of tolerance to the infectious agent must exist. A study of the rate of increase of specific antibody avidity following infection provides a means of assessing the maturity of the immune response to an infectious agent. Since antibodies specific for the HBV core antigen (HBcAg) are produced in almost all cases of HBV infection and the HBeAg and HBcAg share a large number of amino acids and some B- and T-cell epitopes, the increase in the avidity of antibodies against the HBV core antigen (anti-HBc) in cases of acute, resolving HBV infection and in HBV carriers has, therefore, been studied. An increase in the avidity of specific antibody, similar to that seen in other viral infections, was observed following acute, resolving infection. However, low avidity antibody persisted longer in carriers who remained positive for HBeAg, whereas in cases where there were antibodies specific for HBeAg, the anti-HBc antibody was of high avidity. Analysis of sequential sera from carriers who seroconverted from HBeAg-positive to anti-HBe-positive showed that an increase in anti-core avidity could predate seroconversion from HBeAg-positive to anti-HBe-positive status. Thus, anti-HBc avidity studies may be of diagnostic and prognostic significance.

Binding affinities of allergens from pollen, mites, and house dust for specific IgG subclass antibodies

The distribution and affinity of IgG subclasses against various aeroallergens were assessed by inhibition of specific antibody binding. Two parameters from the dose-response curves were taken as indicative of antibody affinity: the point of 50% inhibition and the value of the slopes on double-log plots. It was found that IgG4 antibody specific for aeroallergens (i.e., from pollens of several species of Gramineae, Olea europaea, and Parietaria judaica and from house dust) usually exhibits high affinity, except for Dermatophagoides pteronyssinus. High binding affinity was also displayed by IgG1 subclass antibodies against the allergens of O. europaea and P. judaica. Distinct IgG subclass affinity profiles were observed for the allergens of grass pollen (i.e., Holcus lanatus) and dust mites (i.e., D. pteronyssinus). These results demonstrate that IgG subclass distribution, as well as antibody affinity, depends on the nature of the sensitizing allergen.

Human constant regions influence the antibody binding characteristics of mouse-human chimeric IgG subclasses

Although antibody affinity is primarily determined by immunoglobulin variable region structure human IgG antibodies of the four subclasses specific for the same antigen have been shown to differ in their affinity. To explore the influence of the immunoglobulin constant region on functional antibody affinity, a set of V region identical mouse-human chimeric IgG subclasses specific for TAG72 (tumour-associated glycoprotein) were studied. Biomolecular interaction analysis (BIA) was used to determine the binding kinetics of whole IgG subclasses and F(ab')2 fragments. Despite identical V regions, binding kinetics differed for the four subclasses. The apparent dissociation rate constants of the intact immunoglobulins ranked IgG4 < IgG3 < IgG2 < IgG1. In contrast, analysis of the binding characteriztics of the F(ab')2 fragments derived from IgG1, IgG2 and IgG4 revealed identical binding kinetics. The structure of the constant regions of the humanized IgG subclass antibodies clearly influenced functional antibody affinity, as has been described for the murine IgG subclasses. The exact mechanism for this phenomenon remains obscure but such differences should be taken into account when designing or choosing antibodies for therapeutic use.

Role of beta 2-glycoprotein I in the anticardiolipin antibody affinity for phospholipid in autoimmune disease

The binding capacity to cardiolipin and the functional affinity of affinity-purified anticardiolipin (aCL) IgG of patients with autoimmune disease have been compared with those of individuals with malaria and acquired immunodeficiency syndrome (AIDS). The binding of autoimmune IgG aCL was enhanced gradually by the incorporation of increasing amounts of beta 2-glycoprotein I (beta 2GPI) into the assay, in contrast to that of patients with infectious diseases. In addition, there were significant reductions of functional affinity in autoimmune disease, but not in malaria or in AIDS. These results indicate that beta 2GPI requirement for binding to the target antigen varies inversely with functional affinity in autoimmune disease when beta 2GPI was present, and suggest that IgG aCL are more heterogeneous in this type of disorder than in patients with infectious disease.

Determination of the concentration of influenza virus antihaemagglutinin antibody molecules of the IgG class and of the equilibrium constant by use of enzyme immunoassay titres determined for graded epitope concentrations

A new technique for determining the concentration of influenza virus antihaemagglutinin antibody molecules of the IgG class (A) and of the equilibrium constant K of paratope-epitope interaction is described. The method is based on determining enzyme immunoassay (EIA) titres of antibody with graded epitope concentrations: EIA titres were defined in terms of the antibody dilution yielding a fixed amount of antibody adsorbed per ml (= 6.21 x 10(10)). Adsorption of antibody depends on the concentration of paratopes and epitopes allowed to react and on the equilibrium constant. For the use of a constant concentration of epitopes, the paratope concentration needed to yield the desired degree of antibody adsorption decreases with increasing avidity. Therefore, the EIA titres increase both with increasing avidity and increasing antibody concentration. When graded epitope concentrations are used for determining the EIA titres of a given serum, the titres are influenced in a similar manner by the antibody concentration of the serum and the increase of titres with increasing epitope concentration reflects avidity. The equilibrium constant found is subsequently used to determine the concentration of free antibody at the dilution meeting the definition of EIA titre and the product of EIA titre and the sum of free and bound antibody at this dilution gives the number of antibody molecules present in the test serum. A panel of 118 antisera was tested comparatively for A and K using the new method and by means of the guanidine titre ratio test and equilibrium filtration. The values obtained agreed well with each other. This novel technique offers the advantage that it can be easily adapted for use with other viruses.

Concentration and avidity of anti-tetanus antibodies in mother-infant pairs: relation to immunization time

The concentration and avidity of anti-tetanus antibodies in two groups of mother-infant pairs were compared. Mothers immunized during pregnancy and their newborns (group A) had significantly higher antibody concentrations than mothers immunized at least a year before their last pregnancy and their newborns (group B) as measured by an indirect enzyme immunoassay (EIA) procedure. Antibody avidity of samples was measured by an inhibition EIA technique and urea denaturation test. Although antibody avidity was higher in group B, the differences were not significant. These findings may represent a secondary antibody response to a protein antigen, when considering that all mothers in both groups had received a primary tetanus vaccination during childhood. In mothers with a history of primary tetanus immunization, a single booster dose of tetanus toxoid during pregnancy is enough to induce protective levels of antibodies with reasonably high avidity in both mother and newborn.

Development and preliminary evaluation of an enzyme immunosorbent assay for the detection of adenovirus type 8

Epidemic keratoconjunctivitis (EKC) is a highly contagious adenoviral ocular infection which can occur in outbreaks and is predominantly caused by adenovirus type 8 (Ad8). Detection and typing of this virus after isolation is generally by serum neutralisation or more complex molecular techniques. These methods can be time consuming particularly during outbreaks. Therefore, an Ad8 specific antigen capture enzyme immunosorbent assay (EIA) was developed as a rapid and cost effective diagnostic method for laboratories. An Ad8 type-specific monoclonal antibody was used in a direct antigen capture method and an anti-hapten fluorescein isothiocyanate (FITC)-anti-FITC system. Assay configuration studies indicate that the system in which a type specific capture antibody and a group specific detector antibody are used provides greater sensitivity to the assay than a system using a group specific monoclonal or polyclonal capture antibody. Also, this allows the use of the same detector antibody with varying type specific capture antibodies on the solid phase. In a preliminary evaluation of the two formats, the direct antigen capture assay and the FITC-anti-FITC system had a sensitivity of 98.75% and 100%, respectively, with a specificity of 100%. However, these results are not statistically significant due to the low numbers of Ad8 and other viral isolates obtained from eye swabs. The direct EIA format has been shown to be able to detect different Ad8 genome types including four isolated from four epidemics of EKC in Brest, France, the Ad8 prototype strain, and some DNA-variant isolates which had not been typed by restriction endonuclease analysis (REA).

Specificity of ELISA for IgG subclass antibodies against inhalant antigens in early childhood

ELISA is increasingly used to measure antibodies in new circumstances. Recently, it has been applied to the measurement of IgG subclass antibodies against common antigens in early childhood. These studies have raised concerns about the specificity of some of these assays. This paper details the results of experiments which have assessed the specificity of IgG1 binding to allergens of dust mite (Dermatophagoides pteronyssinus) and ryegrass (Lolium perenne) pollen by inhibition ELISA in the sera of 2-year-old children of atopic parents. Six sera which showed binding of IgG1 to D. pteronyssinus and six to L. perenne were used. All had IgG1 antibody against ovalbumin. In the children's sera, binding to D. pteronyssinus was substantially inhibited by preincubation with the homologous antigen, but not with ovalbumin, thereby confirming the specificity of the assay. However, suppression of IgG1 binding to L. perenne with the homologous antigen was comparatively small, and ovalbumin could cause an equivalent inhibition, indicating poor specificity. Furthermore, the level of IgG1 binding to L. perenne was closely correlated to the level of IgG1 binding to ovalbumin (r = 0.98; P < 0.001). When the assay was reversed, IgG1 binding to ovalbumin was only slightly inhibited by L. perenne, indicating that most antibody binding to ovalbumin was specific. Thus, binding IgG1 in both adult and child sera to D. pteronyssinus appeared to be specific, while child, but not adult, IgG1 binding to L. perenne showed poor specificity. This disparity may be due to differences in the affinities of the respective antibodies, and it illustrates the importance of determining assay specificity when making measurements in early childhood.

Method for determining the equilibrium constant and the concentration of influenza virus IgG antihaemagglutinin antibody molecules by use of EIA titres determined with and without guanidine hydrochloride

A novel technique for determining the concentration of influenza virus antihaemagglutinin antibody molecules (A) of the IgG class and their equilibrium constant (K) is described which is based on recording EIA (enzyme-linked immunosorbent assay) guanidine titre ratios R (EIA titre determined in the absence of guanidine divided by EIA titre determined in the presence of 0.25 M guanidine hydrochloride). K is determined by using a regression line relating values of K to values of R. The line was established by testing antisera comparatively for K by means of equilibrium filtration and for R by EIA. The assay of A is based on the finding that the concentration of antibody molecules adsorbed at serum dilutions yielding an O.D. reading of 0.9 in the EIA test is within the experimental limits constant. Since K is known, this point of reference can be used to calculate A. For a panel of 57 influenza antisera, the A and K values determined by equilibrium filtration agreed well with the respective values determined by use of the novel technique.

Class and subclass distribution of Hantavirus-specific serum antibodies at different times after the onset of nephropathia epidemica

Sera from Dutch and Belgium individuals who suffered from nephropathia epidemica (NE), a mild form of haemorrhagic fever with renal syndrome (HFRS), were tested for the distribution of classes and subclasses of Hantavirus (HV)-specific antibodies at different times after the onset of the disease, with class- and subclass-specific Ig capture enzyme-linked immunosorbent assays (ELISAs). In the acute, early convalescent, and convalescent phases, predominantly specific IgA, IgM, and IgG3 antibodies were detected. Specific IgG2 antibodies were only detected at low levels in the early convalescent and convalescent phases. In the late convalescent phase specific IgG1 and IgG3 antibodies were found, whereas in the late postconvalescent phase only specific IgG1 antibodies proved to be present. Specific IgG4 antibodies were not detected in any of the respective phases. These data show that the simultaneous determination of classes and subclasses of HV specific serum antibodies allows the estimation of the time elapsed after the onset of NE.

Serial functional affinity of autoantibodies in anti-glomerular basement membrane disease

Anti-glomerular basement membrane (GBM) disease is caused by an autoantibody directed against an epitope on the alpha 3 chain of type IV collagen. Animal models demonstrate that the higher the affinity of such antibodies, the greater the degree of glomerular injury. Affinity maturation (the process whereby somatic mutation followed by antigen selection leads to an increase in affinity of antibody) might therefore be of pathogenic significance if it occurs in human anti-GBM disease. We have examined serial samples from nine patients with anti-GBM disease and looked for evidence of changing functional affinity by measuring the inhibition of binding produced by the mild chaotrope diethylamine (DEA) in an anti-GBM antibody ELISA. Seven patients showed no change in the inhibition produced by DEA with time. Two patients showed an apparent decrease with time in the inhibition produced by DEA; this apparent increase in functional affinity proved, on further investigation, to represent simply the loss of anti-GBM antibodies. These results may imply that affinity maturation has been completed by the time that patients present with anti-GBM disease. If there had been evidence for a further increase in functional affinity after this point then this might have added extra urgency to the need for removal of these autoantibodies as part of treatment.

Trypanosoma cruzi infection in mice induces a polyisotypic hypergammaglobulinaemia and parasite-specific response involving high IgG2a concentrations and highly avid IgG1 antibodies

Trypanosoma cruzi infection in BALB/c mice induced a reversible polyisotypic hypergammaglobulinaemia, with particularly high levels of IgG2a, IgM and IgE. Hypergammaglobulinaemia started during the acute phase of infection and persisted during chronic disease until 11-13 weeks post-infection (w.p.i.), when immunoglobulin levels, with the exception of IgE, returned near normal values. Parasite-specific antibodies counted for 14 to 23% of gammaglobulinaemia, in acute and chronic infection respectively. The titres of IgM antibodies rose from two w.p.i. IgA, IgE and IgG subclass antibodies built up gradually over the time of parasite clearance (i.e., between three and six w.p.i.). All antibody isotypes, including IgM reached significant and stable titres throughout chronic infection. IgG2a, IgG1 and IgM antibodies had constantly higher titres than the other antibody isotypes. The dominance of IgG2a antibodies was due to their high plasma concentrations, around 70% of all antibodies available in the chronic infection. IgG1 had the highest functional avidity, whereas its concentration corresponded to only 10% of the whole antibody fraction. These results indicate that T. cruzi infection in mice induces a polyisotypic humoral immune response, dominated by some antibody isotypes, with major differences in concentrations and functional avidities. This could be of crucial importance in determining the outcome of infection.

Evaluation of protein-denaturing immunoassays for avidity of immunoglobulin G to rubella virus

Immunoassays have been recently developed that measure the avidity of IgG antibodies to complex microbial antigens and are suitable for serologic diagnosis of infectious diseases. In these avidity ELISAs, protein-denaturing agents are applied either as diluents of patient sera to prevent the immune complexing of IgG (diluting principle), or the preformed complexes are treated with the protein denaturants (eluting principle). We compared four protein denaturants previously used in such assays, in a diagnostic avidity ELISA for rubella IgG. Diethylamine, guanidine, thiocyanate, or urea were applied, by either principle at various concentrations, and thiocyanate, or urea were applied, by either principle at various concentrations, and thiocyanate at an optimum pH. Patient sera obtained recently after primary infection were distinguished from sera representing past rubella immunity by any protein denaturant tested by the eluting principle, which was superior to the diluting principle.

Low antibody affinity restricted to the IgA isotype in IgA nephropathy

Antibody affinity affects the handling and behaviour of immune complexes, and experimental studies have shown that animals which produce predominantly low-affinity antibody are prone to immune complex deposition resulting in glomerulonephritis. In order to investigate the potential role of antibody affinity in the pathogenesis of IgA nephropathy, affinity of both IgA and IgG antibody isotypes during secondary response to systemic immunization with tetanus toxoid was studied in 20 patients with IgA nephropathy. Patients with IgA nephropathy produced IgA antibodies of significantly lower affinity than controls (P < 0.001), whereas IgG antibody affinities were similar. Contrasting with controls, patients' IgA antibody affinity was inversely related to antibody concentration, with higher responders producing large amounts of low-affinity antibody. IgG antibody affinity increased with time, and maturation of IgG antibody affinity was similar in both controls and patients. IgA affinity in controls decreased with time, and this lack of IgA affinity maturation may explain the relative unimportance of IgA in normal systemic immunity. This temporal decrease in IgA affinity was not observed in patients with IgA nephropathy. The production of low-affinity IgA in IgA nephropathy may provide an explanation for the predominant deposition of IgA in this disease.

The role of pH in modified ELISA procedures used for the estimation of functional antibody affinity

Solid phase assays for the measurement of functional antibody affinity are increasingly being used in both clinical and research settings. The majority of such assays employ a chemical reagent to disturb antibody binding but relatively little is known about the properties of such reagents and the basis of their effect on antigen-antibody binding. We have evaluated the diethylamine (DEA) ELISA procedure for the measurement of functional antibody affinity in two independent assays, one for functional human IgG subclass affinity to an organism, Moraxella catarrhalis, and the other for measuring functional affinity of mouse monoclonals specific for the cat allergen Fel d I. DEA was shown to increase the pH of the buffering solution and it was this rise in pH that affected antibody binding. Alkaline buffer and DEA were equally efficient in the inhibition of binding of both the human IgG subclasses and the two mouse monoclonal antibodies to the solid phase. In contrast, pH was shown to have no role in the chaotropic effect of the ion, thiocyanate.

The functional affinities of antibodies of different IgG subclasses to dietary antigens in mothers and their babies

The quantity and functional affinities of IgG1 and IgG4 antibodies to the dietary antigens casein and ovalbumin were measured in unselected mothers and their 1-year-old infants. In these infants, the titre of IgG antibodies to both antigens was highest in the IgG1 subclass, while in their mothers the titre of IgG1 and IgG4 antibodies to these foods was similar. High affinity IgG4 responses to both casein and ovalbumin were frequently found in mothers, whilst IgG1 responses, particularly to ovalbumin, were of low functional affinity. By contrast, in the 1-year-old infants, the functional affinity of IgG1 antibody to ovalbumin was substantially higher than in their mothers (Student's paired t-test, P < 0.001), indicating that higher affinity IgG1 antibody was produced on first exposure to ovalbumin rather than following chronic exposure. The effect of antigenic load on affinity maturation was further investigated by comparing the affinity of IgG1 antibody to casein in bottle, mixed and breast fed infants. Bottle fed infants had significantly higher-affinity IgG1 antibodies to casein compared with breast or mixed fed infants (Student's unpaired t-test, P < 0.01 and 0.02), suggesting that antigen exposure via the gut was able to drive the affinity maturation process. In studying the immune response it is clear that account must be taken of the affinity as well as of the titre of the antibody produced.

Problems and pitfalls with measurement of antibody affinity using solid phase binding in the ELISA

Current methods of estimation of antibody affinity constants using ELISA assume homogeneous binding of antibody to the solid phase, despite many reports in the literature that this is not true. I have derived theoretical antibody binding curves for solid phase antigen assuming homogeneous antibody binding. I have compared these curves with a set of experimental binding curves of monoclonal antibodies to the serum protein fibronectin. The results conclusively show that while some monoclonal antibodies behave as predicted by theory, others show departures from homogeneous binding which can be explained by various surface effects. I have discussed how these surface effects can cause errors in estimates of either liquid phase or solid phase affinities using the ELISA, and have demonstrated the limitations of methods of affinity ranking.

Antimitochondrial autoantibodies in anti-glomerular basement membrane disease

Anti-glomerular basement membrane (GBM) disease is characterized by the production of an autoantibody with very restricted specificity, with no evidence of polyclonal B cell activation. It was therefore surprising to find that in a solid-phase ELISA a proportion of anti-GBM sera showed significant binding to pyruvate dehydrogenase (PDH), a reactivity usually associated with the antimitochondrial autoantibodies (AMA) found in primary biliary cirrhosis (PBC). The specificity of this reactivity was confirmed by inhibition and competition experiments. The AMA found in anti-GBM sera were of much lower affinity than those found in PBC sera, and recognized a more restricted set of species (mainly the 55-kD and occasionally the 74-kD component of PDH). However, it was possible to block the binding in a Western blot of an anti-GBM serum to both the 55-kD and 74-kD species with F(ab')2 fragments prepared from a PBC serum. Although AMA have been found in diseases other than PBC, such diseases have usually been characterized by polyclonal B cell activation. The stimulus to the production of AMA in anti-GBM disease, and their significance in pathogenesis (if any), are unknown.

Time course of hepatitis A antibody production after active, passive and active/passive immunisation: the results are highly dependent on the antibody test system used

Two commercially available automated test systems for hepatitis A antibody, HAVAB IMX (Abbott) and ENZYMUN Anti-HAV (Boehringer) were evaluated in a study of active, passive and active/passive immunisation against hepatitis A. The inactivated hepatitis A vaccine Epaxal Berna and the hepatitis A immunoglobulin preparation Globuman were products of the Swiss Serum and Vaccine Institute. Although both hepatitis A antibody test kits were standardised with the same international WHO standard hepatitis A immunoglobulin preparation, divergent results were obtained for the level of circulating hepatitis A antibody after vaccination. One month after the vaccination the mean geometric antibody titres were 315 mIU/ml after active, 253 mIU after active/passive and 22 mIU after passive immunisation when measured with the Enzymun assay. In the same sera 70 mIU/ml after active, 60 mIU after active/passive and 18 mIU after passive immunisation could be detected with the IMX test. Antibody avidity studies could not explain the differences obtained by the two test methods. The neutralization test is the standard method for the estimation of protection against hepatitis A. This test is not suitable for large series of serum samples, and enzyme immunoassays are indispensable for vaccination studies. To be suitable for monitoring antibody development in phase I and II clinical trials as well as in postmarketing studies, EIA tests for hepatitis A antibodies must be commercially available and of known sensitivity. The Enzymun anti-HAV test developed by Boehringer Mannheim (Germany) offers the possibility to measure antibody titres around the protective level of 20 mIU/ml which is reached by the passive immunisation with immunoglobulin preparations or within two weeks after active vaccination with an inactivated hepatitis A vaccine. The Abbott IMX test system is more useful for the detection of natural infections by the hepatitis A virus.

Calculation of the affinity constant KASS for solid phase antigen. A model system using monoclonal antibodies against the cat allergen Fel d I

In this report a procedure is described to calculate the affinity constant of an antibody for solid-phase Ag. KSP (KASS solid phase) was defined as the reciprocal of the concentration of Ag required for half saturation of the Ab-binding sites, extrapolated to an infinitely small concentration of Ab (semi-saturation plot). Using this procedure, the affinity of IgE antibodies can be measured without interference from 'invisible' IgG antibodies. As a model system, mAbs against the cat allergen Fel d I were used. Serial dilutions of Fel d I-Sepharose were incubated with serial dilutions of mAb Fd1a and Fd1b, with or without rabbit antibodies as 'invisible' antibodies. The Ab-binding capacity of Sepharose-coupled Fel d I was low: 4.15% and 2.13% of the expected value for mAb Fd1a and Fd1b, respectively, and this must be taken into account when calculating KSP. The K values of mAb Fd1a and Fd1b, calculated from the gamma axis intercept of the semi-saturation plot, were 85 (pmol/test)-1 and 65 (pmol/test)-1 respectively. Using the semi-saturation plot, KSP of mAb Fd1a was not affected by the presence of rabbit antibodies against Fel d I, confirming the applicability of the procedure for measuring the KSP of IgE in patient sera. For one cat-allergic patient the KSP of IgE and IgG4 for Fel d I were calculated and found to be 62 (pmol/test)-1 and 147 (pmol/test)-1 for IgE and IgG4 respectively.

Suppression of collagen induced arthritis by oral administration of type II collagen: changes in immune and arthritic responses mediated by active peripheral suppression

The oral administration of CII by gavage to WA/KIR rats before a conventional arthritogenic challenge with bovine CII in FIA reduced the incidence (by 23%) and delayed the onset of collagen-induced arthritis in about 50% of the animals. Selective changes in B cell and T cell responses to CII in animals treated this way are interpreted to indicate a state of tolerance or hyporesponsiveness to CII. Tolerant animals made less serum antibody, to bovine and rat CII, of the IgG2b isotype and more of the IgG1 isotype. Phenotypic and functional analysis of peripheral lymph node cells showed that those from tolerized animals expressed less MHC Class II, proliferated less and secreted less IgG2b anti-CII antibody in response to stimulation in vitro with CII when compared with cells from non-tolerant animals. However, this depression of the immune responses to CII seen in vitro was overcome when the cells were incubated with increasing amounts of CII. Tolerance could be transferred to normal animals. Spleen cells, and nylon wool-filtered splenic T cells (but not mesenteric lymph node cells) adoptively transferred hyporesponsiveness to normal recipients which were then less susceptible to collagen-induced arthritis. Transfer of serum from gavaged animals did not modify the susceptibility of normal recipients to arthritis. Spleen cells from gavaged animals suppressed proliferative and antibody responses in co-cultures in vitro with lymph node cells from animals immunized with CII in FIA. The suppressive spleen cell population contained more cells expressing MHC Class II, in both the CD8+ and CD4+ populations. These studies show that the oral administration of CII alters the subsequent immune response to the arthritogenic challenge and indicate that this oral tolerance of CII is due, not to clonal deletion or anergy, but rather to an antigen-driven active suppression mechanism that affects both T cells and B cells, most likely through the action of regulatory cytokines IL-4, IL-10 and TGF beta.

Avidity and titer of immunoglobulin G subclasses to Porphyromonas gingivalis in adult periodontitis patients

The relative avidity and titer of antibodies representing the 4 immunoglobulin G (IgG) subclasses (IgG1-4) reactive with Porphyromonas gingivalis, P. gingivalis-lipopolysaccharide (-LPS), streptokinase (SK) and tetanus toxoid (TT) in the sera of patients having adult periodontitis and of healthy controls were measured. Patient antibody titers to P. gingivalis and P. gingivalis-LPS were found to be significantly elevated for IgG, IgG1 (no P. gingivalis-LPS antibodies) and IgG2. The predominant antibody response to P. gingivalis and P. gingivalis-LPS occurred in the IgG2 subclass. When the relative avidity of the antibodies to P. gingivalis and P. gingivalis-LPS were examined, no significant differences between control and patient sera could be identified. However, anti-P. gingivalis and P. gingivalis-LPS antibodies were found to possess significantly lower relative avidity than either SK or TT antibodies. The IgG1 subclass antibodies to P. gingivalis, SK and TT all appeared to be of high relative avidity. In contrast, anti-P. gingivalis and P. gingivalis-LPS of the IgG2 subclass were of significantly lower relative avidity. Since the predominant humoral response to P. gingivalis occurs in the IgG2 subclass, the low relative avidity of these antibodies predominates in measurements of whole serum activity.