Avidity of immunoglobulin G to rubella virus in post-vaccination and post-infection immunity

Comparative evaluation of avidity of IgG to rubella virus in vaccinated persons, in patients with rubella or other exanthematous illness, and in healthy persons revealed similar patterns in post-vaccination and post-infection immunity. Virus specific low avidity IgG (index of avidity < or =30%) were detected in patients with rubella during 7 weeks after symptoms appeared as well as in vaccinated persons which were tested 6 weeks after vaccination. Low avidity antibodies in sera were detected in 96% of patients with rubella and in 75% of vaccinated persons which were not immune before immunization. Live attenuated vaccines Ervevax, Priorix, and MMR-II had similar ability to induce low avidity IgG to rubella virus. Increase of low avidity antibodies concentration was noted after immunization of children with low levels of antibodies before vaccination. After immunization of persons with high avidity antibodies in serum, index of avidity remained above threshold. Anamnestic high avidity IgG (index of avidity 51-100%) were detected in majority of immune healthy persons (96.4%) as well as in patients with exanthematous illnesses not related to rubella infection (93.6%). ELISA test-systems for detection of low avidity IgG to rubella virus allow to obtain reliable information about seroconversion rate and characteristics of immune response in vaccines. Detection of low avidity IgG in serum obtained 5-6 weeks after immunization points to primary immune response, whereas identification of high avidity antibodies reveals already immune persons.     

Differential responsiveness to immunoablative therapy in refractory rheumatoid arthritis is associated with level and avidity of anti-cyclic citrullinated protein autoantibodies: a case study

In order to identify pathogenic correlates of refractory rheumatoid arthritis (RA), antibodies against anti-cyclic citrullinated protein (ACPAs) were investigated in RA patients in whom the dysregulated immune system had been ablated by high-dose chemotherapy (HDC) and autologous haematopoietic stem cell transplantation (HSCT). Six patients with refractory RA were extensively characterized in terms of levels of total immunoglobulins, RA-specific autoantibodies (ACPAs and rheumatoid factor) and antibodies against rubella, tetanus toxoid (TT) and phosphorylcholine before and after HDC plus HSCT. Additionally, the avidity of ACPAs was measured before and after treatment and compared with the avidity of TT antibodies following repeated immunizations. Synovial biopsies were obtained by arthroscopy before HDC plus HSCT, and analyzed by immunohistochemistry. In the three patients with clinically long-lasting responses to HDC plus HSCT (median 423 days), significant reductions in ACPA-IgG levels after therapy were observed (median level dropped from 215 to 34 arbitrary units/ml; P = 0.05). In contrast, stable ACPA-IgG levels were observed in three patients who relapsed shortly after HDC plus HSCT (median of 67 days). Clinical responders had ACPA-IgG of lower avidity (r = 0.75; P = 0.08) and higher degree of inflammation histologically (r = 0.73; P = 0.09). Relapse (after 38 to 530 days) in all patients was preceded by rising levels of low avidity ACPA-IgG (after 30 to 388 days), in contrast to the stable titres of high avidity TT antibodies. In conclusion, humoral autoimmune responses were differentially modulated by immunoablative therapy in patients with synovial inflammation and low avidity ACPA-IgG autoantibodies as compared with patients with high levels of high avidity ACPA-IgG. The distinct clinical disease course after immunoablative therapy based on levels and avidity of ACPA-IgG indicates that refractory RA is not a single disease entity.     

The role of IgG avidity in diagnosis of cytomegalovirus infection in newborns and infants

To evaluate the value of IgG avidity in diagnosis of congenital cytomegalovirus (CMV) infection in newborns and infants we collected serum samples from 40 infants under 12 months of age with suspected congenital CMV infection. Sera were tested for IgM, IgG and IgG avidity. For 25 of them, virus isolation and/or polymerase chain reaction (PCR) on urine specimens were performed. Thirteen (32.5%) patients showed the presence of CMV IgM antibodies, 3 (7.5%) had equivocal IgM result, and 24 (60.0%) patients had IgG antibodies only. Using IgG avidity, CMV infection (low avidity index-AI) was documented in 61.5% IgM positive and 54.2% IgM negative patients. Eight of nine (88.8%) IgM positive patients were positive either on virus isolation or PCR. In IgM negative patients, 46.6% urine cultures were positive for CMV and 66.6% were PCR positive. According to age, IgG avidity demonstrated acute/recent primary CMV infection in 58.8% patients younger than three months compared with 91.7% and 81.8% in 3-6 and 6-12 months old babies, respectively. In conclusion, IgG avidity is useful in diagnosis of CMV infection either in IgM positive or IgM negative children older than 3 months of age. In infants less than 3 months, transplacentally derived maternal IgG antibodies of high avidity influence on the IgG avidity result. In these children, CMV infection should be confirmed by direct virologic methods such as virus isolation or PCR.     

Determination of serum antibody avidity compared to infectious O-antigenemia in paratyphoid B patients

The avidity of serum antibodies depending on infectious O-antigenemia in patients with paratyphoid B has been studied in the course of the disease. The study has revealed a faintly pronounced inverse correlation between the degree of avidity of serum antibodies and the level of infectious antigenemia. The avidity of serum antibodies in paratyphoid B has been found to increase in the course of the disease. A significant dependence of the severity of the disease on the avidity of serum antibodies has been noted.     

IgG Avidity Antibodies against Toxoplasma gondii in High Risk Females of Reproductive Age Group in India

Toxoplasma gondii is an obligate intracellular protozoan that is distributed worldwide. Recently, several tests for avidity of Toxoplasma IgG antibodies have been introduced to help discriminate between recently acquired and distant infections. The study was conducted in Jawaharlal Nehru Medical College and Hospital, India from February 2011 to September 2012. Serum specimens were subjected to Toxoplasma IgM ELISA and IgG avidity ELISA test. Out of 48 patients with abortions, 17 (35.4%) were positive for IgM ELISA, and 8 (16.6%) had low IgG avidity antibodies. Out of 48 patients with other obstetric problems, 23 (47.9%) were positive for IgM ELISA, and 17 (35.4%) had low IgG avidity antibodies. Combining both groups on avidity test, only 25 of 40 (62.5%) IgM-positive women had low-avidity IgG antibodies suggesting a recent T. gondii infection in these women. More importantly, 15 (37.5%) of the IgM-positive women had high-avidity antibodies suggesting that the infection was acquired before gestation The relation of IgM seropositivity with the following risk factors was not found to be statistically significant; contact with cats (0.13), non-vegetarian food habits (0.05), and low socio-economic status (0.49). While, for IgG avidity ELISA, only contact with cats (0.01) was significantly associated with seropositivity. All other risk factors have P-values of >0.05 (not significant). IgG avidity test when used in combination with IgM test was a valuable assay for diagnosis of ongoing or recently acquired T. gondii infection in India.     

Characterization of antibody response to Pseudomonas aeruginosa in patients with wound infections

ELISA was used to measure the amount and avidity of IgG antibodies to exotoxin A (ExA) and 7 Fisher's immunotypes of lipopolysaccharide (LPS) in the sera of 13 patients with mild or moderate Pseudomonas aeruginosa infections. Changes in the specificity of tested sera during the course of infection were demonstrated. A statistically significant increase was seen in the amount and avidity of the antibodies to ExA in a majority of the sera, and an increase was seen in amount of antibodies to LPS immunotype 4 in the sera of patients with moderate infections.     

Avidity of onconeural antibodies is of clinical relevance

Onconeural antibodies are important in the detection of paraneoplastic neurological syndromes (PNS). The avidity of Hu, Yo, and CRMP5 antibodies from 100 patients was determined by immunoprecipitation (IP), and 13 of the Yo positive sera were also tested by surface plasmon resonance (SPR). There was a significant association between the results from IP and SPR. Yo antibodies had higher avidity than Hu and CRMP5 antibodies, and both high- and low-avidity antibodies were associated with tumors and PNS. High-avidity Yo antibodies were mainly associated with ovarian cancer, whereas high-avidity Hu and CRMP5 antibodies were mainly associated with small-cell lung cancer. Low-avidity CRMP5 and Yo antibodies were less often detected by a commercial line blot than high-avidity antibodies. The failure to detect low-avidity onconeural antibodies may result in under diagnosis of PNS.     

The role of IgG avidity determination in diagnosis of Epstein-Barr virus infection in immunocompetent and immunocompromised patients

There is a high degree of variability in the serologic response to Epstein-Barr virus (EBV) infection, especially in viral capsid antigen (VCA)-IgM antibodies. Therefore, additional tests are needed to confirm primary infection. We evaluated the value of IgG avidity determination in diagnosis of EBV infection in immunocompetent and immunocompromised patients. A total of 236 serum samples from immunocompetent patients with symptoms suggestive of EBV infection were tested for the presence of VCA-IgM/IgG antibodies and IgG avidity. Using IgG avidity, acute primary infection was confirmed in 56.7% of the immunocompetent patients with positive and in 1.8% of patients with negative VCA-IgM. Recent primary infection was documented in 8.9% of the IgM positive and 3.5% of the IgM negative patients. In patients with indeterminate serology (equivocal IgM), 6.7% were classified by avidity index (AI) as acute primary infection, 10.0% as post-acute and 83.3% as past infection cases. Concerning the 32 immunocompromised patients, recent primary infection was documented in 3 of the 14 IgM positive patients. High AI was detected in 11 of these patients, indicating an IgM response due to reactivation. Determination of IgG avidity in combination with classical serologic markers seems to be a reliable method to confirm primary infection both in immunocompetent and immunocompromised patients. It may be especially useful to differentiate cases of primary infection in patients with undetectable VCA-IgM antibodies or indeterminate routine EBV serology.     

Avidity of bivalent antibodies. Problems of its experimental determination and theoretical evaluation

Some problems of experimental determination or theoretical evaluation of antibody avidity are considered. It was shown that in order to determine the fraction of nonoccupied antibodies in their mixture with the excess of the corresponding antigen which is required to estimate avidity the methods should be used which are more sensitive than ELISA. The available methods did not allow determining the avidity of bivalent antibodies because of many reasons. However, in the recent years new methods were suggested that make it possible to evaluate the avidity of bivalent antibodies and that of the receptors which consist of two binding sites connected by a flexible linker of the known length. Thus, there are all possibilities now for determining the avidity of bivalent antibodies in experiments or by theoretical methods.     

Antibody avidity indices of the saliva and serum antibodies in salmonellosis patients

The avidity characteristics of salivary and serum antibodies have been determined in 179 salmonellosis patients by means of the indirect hemagglutination inhibition test. These investigation have shown that, in contrast to serum antibodies, no changes occur in the avidity of salivary antibodies in the course of the disease. This is due to the fact that secretory antibodies belong to IgA which have no tendency to ripening. The regularities thus established reflect the role of secretory and serum antibodies in the pathogenesis of Salmonella infections.     

Performance of the immunoglobulin G avidity and enzyme immunoassay IgG/IgM screening tests for differentiation of the clinical spectrum of toxoplasmosis

Toxoplasmosis has been well known as an important human infection to consider especially in pregnant women. Although many serologic methods are available, the diagnosis of toxoplasmosis can be extremely difficult. The presence of increased levels of Toxoplasma-specific IgG antibodies indicates an infection, but it does not differentiate between a recent and past infection. The purpose of our study was to compare the performance of the ELISA T. gondii IgG/IgM test, a widely used enzyme-linked immunosorbent assay, to the ELISA IgG avidity method. One hundred and four serum samples (from 38 males and 66 females) were tested and evaluated from symptomatic patients (chorioretinitis, lymphadenopathy), and from women in their first trimester of pregnancy who were suspected of having toxoplasmosis. The high IgG avidity and ELISA IgG antibody levels were in agreement for 51 of the specimens (49.0%). Thirty-eight discrepant (borderline) results from the IgG avidity method were positive for IgM (3 specimens) and IgG (37 specimens). Interestingly, out of the eight serum samples that were positive for both IgG and IgM antibodies, two samples were low IgG avidity, and three samples were borderline. There was no statistically significant relation observed between the results of the IgG avidity method and the ELISA IgG test, and the IgG avidity method and ELISA IgM test (chi2 = 1.987; p = 0.370 and chi2 = 2.152; p = 0.341, respectively). The IgG avidity method was considered easy to perform and an acceptable approach for the differentiation of discrepant results (recent/chronic) and for the current detection of T. gondii antibodies. We concluded that the determination of IgG avidity is a helpful tool for the diagnosis of the ocular form of toxoplasmosis and it is a safe method for screening this disease in the first trimester of pregnancy.     

A role for nonprotective complement-fixing antibodies with low avidity for measles virus in atypical measles

In the 1960s, a formalin-inactivated measles vaccine (FIMV) predisposed recipients to atypical measles, an immune complex-mediated disease. To identify characteristics of the immune priming that leads to atypical measles, responses of monkeys to FIMV were compared with responses to live attenuated virus (LAV) and hemagglutinin (H-DNA) vaccines that do not prime for atypical measles. Antibodies induced by FIMV were transient and avidity did not mature. Antibodies induced by LAV and H-DNA vaccines were sustained and avidity matured over time. After challenge with measles virus, FIMV and H-DNA recipients developed high titers of complement-fixing antibodies. In FIMV recipients, the antibodies were of low avidity, whereas in H-DNA vaccine recipients, the antibodies were of high avidity. Neutralizing capacity in B958 cells correlated with avidity. Only FIMV recipients had immune complex deposition. Failure of FIMV to induce affinity maturation results in anamnestic production of nonprotective, complement-fixing antibodies, immune complex deposition and atypical measles.     

Detection of antibodies to DNA: a technical assessment.

Antibodies to DNA can be found in the circulation of the majority of patients with Systemic Lupus Erythematosus (SLE). They are quite specific for this disease, which makes their detection an important diagnostic aid to the clinician. Fluctuations in the level of anti-dsDNA in an individual patient generally parallel the clinical state of that patient. Furthermore, the presence of anti-dsDNA may precede the diagnosis of SLE by more than a year. Four methods relevant for the measurement of anti-dsDNA antibodies are discussed in this paper: the ELISA, the indirect immunofluorescence test on Crithidia luciliae, the PEG assay, and the Farr assay. Each of these methods detects a part of the spectrum of anti-dsDNA antibodies present in the circulation of an individual patient. The ELISA is the most sensitive method, whereas the Farr assay is the most specific for SLE. However, with the latter method only antibodies of a relative high avidity for DNA are detected. Mild forms of SLE, where patients only have anti-dsDNA of a low avidity in their circulation, may easily be missed by this technique. Clinically, high avidity anti-dsDNA is related with the more frequent occurrence of nephritis, whereas low avidity anti-dsDNA antibodies are more often found in patients with central nervous system involvement.     

Complement-mediated solubilization of immune precipitates prepared with antibodies of different avidity.

Complement-mediated solubilization of immune precipitates prepared with HSA and rat IgG anti-HSA has been quantitatively analyzed. Early and late IgG anti-HSA antibodies were obtained 27 and 49 days after immunization, respectively. Immune precipitates prepared with early IgG anti-HSA were solubilized by rat serum to a larger extent than complexes prepared with late IgG anti-HSA. The affinities for HSA of the early and late antibodies were not significantly different. The quantitative differences in solubilization were neither due to differences in the Ab/Ag ratios of the immune precipitates, nor appeared to be brought about by changes in the distribution of the antibodies over the IgG sub-classes. The avidity of the late IgG anti-HSA antibodies was higher than the avidity of the early IgG antibodies. Presumably, the avidity of the antibodies greatly affected the complement-mediated solubilization of the immune precipitates. In addition, the solubilization was found to be dependent on the conditions employed to prepare the immune precipitates.     

Neutralization of bacterial viruses by antibodies of young animals

The development of the avidity of 19S and 7S neutralizing antibodies was studied after the immunization of young rabbits with ΦX 174 bacteriophage. Both 19S and 7S antibodies formed during the entire course of the immunization process were able to neutralize bacteriophage ΦX 174 without the participation of thermolabile serum components: neither heat inactivation at 56°C nor addition of piglet complement into the neutralizing system influenced the titer in the neutralization test. In both immunoglobulin classes (IgM and IgG) the first antibodies formed possessed a low avidity that increased in the course of the immunization process so that in the secondary response antibodies of both 19S and 7S type were formed possessing a high binding activity towards the specific antigen. Following the immunization with a high dose of the phage antigen (10¹⁰ PFU of ΦX 174 phage) 19S antibodies were formed at a relatively fast rate, the avidity of which did not further increase during immunization. When a low antigen dose was used for immunization the avidity of antibodies significantly increased in the course of immunization.     

Determination of specific immunoglobin G avidity in serodiagnosis of toxoplasmosis

A total of 37 serum samples from pregnant women were examined for the avidity of toxoplasma IgG antibodies using commercially available enzyme immunoassay (Vidas Toxo IgG Avidity, bio Merieux). Low values of the avidity index were found for 4 samples and borderline ones were found in further 3 cases. Out of 19 serum samples showing the presence of IgG and IgM toxoplasma antibodies, 13 had high avidity index, including 9 samples from women in the first trimester of pregnancy. The results of examinations in these 9 cases allowed to exclude the possibility that toxoplasma infection was acquired during gestation. It is to be concluded that determinations of antitoxoplasma IgG avidity should become routine in every pregnant woman positive in the test for specific IgM antibody.     

Humoral recall responses in HIV infection. Levels, specificity, and affinity of antigen-specific IgG

To evaluate the integrity of humoral immunologic memory among persons with HIV infection, we measured the levels, specificity, and functional affinity of circulating antibodies to vaccine-related recall Ag, tetanus (TT) and diphtheria toxoids (DT), and to naturally acquired measles virus, in sera from 17 HIV-seronegative control subjects, 17 asymptomatic HIV-seropositive patients, and 10 patients with AIDS. Preimmunization levels of TT- and measles-specific IgG were similar in all groups, although DT-specific IgG was lower in AIDS patients. Four wk after immunization with TT3 and DT, all groups showed significantly increased specific antibody levels (p less than 0.02). The asymptomatic HIV+ patients and control subjects achieved similar peak serum levels of TT-specific IgG (102 +/- 32 and 169 +/- 36 micrograms/ml, respectively). In contrast, the AIDS patients had lower peak values of both TT- and DT- specific IgG (p less than 0.05). Peak levels correlated directly with the number of CD4+ T cells (p less than 0.05). However, 80 to 100% of all participants tested, independent of HIV status, showed higher levels of TT- and DT-specific IgG 6 mo after immunization compared with preimmunization levels. The antitoxoid antibodies were specific as they did not cross-react with other Ag in competitive inhibition experiments. In addition, all groups exhibited antibodies to TT and DT both pre- and postimmunization of equivalent functional affinity (avidity) (Kd = 10(-10)-10(-11) mol/liter). We conclude that, in contrast to the profoundly depressed humoral responses to new Ag, persons with asymptomatic HIV infection retain humoral immunity to certain recall Ag. These levels of specific IgG to three recall Ag are not proportional to elevated levels of total serum IgG in HIV-infected patients. In addition, many patients with HIV respond to challenge with recall Ag by producing significant amounts of high affinity IgG that may persist over time.     

Follow-up of antibody avidity in BALB/c mice infected with Toxocara canis

In human Toxocara canis infection, an association has been shown between high IgG avidity in the chronic phase and low IgG avidity in recently acquired toxocarosis. The evolution of the antibody response in terms of avidity has been carried out through a T. canis infection in BALB/c mice. Infection with T. canis embryonated eggs (EE) was carried out with single doses (SD) of 6, 12, 50, 100, 200 or 1000 EE/mouse and with multiple doses (MD) of 200 and 1000 EE. Specific antibodies against T. canis (IgM+G, IgG, IgG1 and IgM) were detected by ELISA and Western Blot (WB) techniques in the presence and absence of urea. With the ELISA method, an increase in the avidity index (AI) of around 50% was detected from days 40-80 p.i. to the end of the study, with all the doses studied. The WB method showed the presence of high avidity antibodies bound to 100 kDa and 75 kDa T. canis proteins in all the cases when the IgM+G and the IgG1 antibodies were investigated. Antibodies of variable avidity were observed in those sera that recognized the group of low molecular weight proteins, between 37 kDa and 25 kDa.     

Diagnosis of toxoplasmosis in pregnancy: importance of immunoglobulin G avidity test

The immunoglobulin G (IgG) avidity test has proved to be a highly useful test in the diagnosis of toxoplasmosis during pregnancy, especially in combination with conventional serological assays. Acute infections at the time of gestation predispose the offspring to the risk of congenital toxoplasmosis. The IgG avidity test was developed to differentiate between recent and more distant infection; this method is valuable in the situation in which a single serum sample is obtained in the first trimester of pregnancy. This paper describes the utility of IgG avidity test during pregnancy, and its role in ruling out, by a high avidity, a recently acquired infection. Testing for specific IgG avidity has been reported to be useful for confirmatory testing in patients who have positive IgG and IgM antibodies.     

Antigen-Specific Memory B-cell Responses to Enterotoxigenic Escherichia coli Infection in Bangladeshi Adults

Background

Multiple infections with diverse enterotoxigenic E. coli (ETEC) strains lead to broad spectrum protection against ETEC diarrhea. However, the precise mechanism of protection against ETEC infection is still unknown. Therefore, memory B cell responses and affinity maturation of antibodies to the specific ETEC antigens might be important to understand the mechanism of protection.

Methodology

In this study, we investigated the heat labile toxin B subunit (LTB) and colonization factor antigens (CFA/I and CS6) specific IgA and IgG memory B cell responses in Bangladeshi adults (n = 52) who were infected with ETEC. We also investigated the avidity of IgA and IgG antibodies that developed after infection to these antigens.

Principal Findings

Patients infected with ETEC expressing LT or LT+heat stable toxin (ST) and CFA/I group or CS6 colonization factors developed LTB, CFA/I or CS6 specific memory B cell responses at day 30 after infection. Similarly, these patients developed high avidity IgA and IgG antibodies to LTB, CFA/I or CS6 at day 7 that remained significantly elevated at day 30 when compared to the avidity of these specific antibodies at the acute stage of infection (day 2). The memory B cell responses, antibody avidity and other immune responses to CFA/I not only developed in patients infected with ETEC expressing CFA/I but also in those infected with ETEC expressing CFA/I cross-reacting epitopes. We also detected a significant positive correlation of LTB, CFA/I and CS6 specific memory B cell responses with the corresponding increase in antibody avidity.

Conclusion

This study demonstrates that natural infection with ETEC induces memory B cells and high avidity antibodies to LTB and colonization factor CFA/I and CS6 antigens that could mediate anamnestic responses on re-exposure to ETEC and may help in understanding the requirements to design an effective vaccination strategies.