Immunoglobulin-A detection and the investigation of clinical toxoplasmosis

Multiplexed Anti-Toxoplasma IgG, IgM, and IgA Assay on Plasmonic Gold Chips: towards Making Mass Screening Possible with Dye Test Precision

Toxoplasmosis is an infection caused by the protozoan parasite Toxoplasma gondii that can lead to severe sequelae in the fetus during pregnancy. Definitive serologic diagnosis of the infection during gestation is made mostly by detecting T. gondii-specific antibodies, including IgG and IgM, individually in a single serum sample by using commercially available kits. The IgA test is used by some laboratories as an additional marker of acute infection. Most of the commercial tests have failed to reach 100% correlation with the reference method, the Sabin-Feldman dye test for the detection of Toxoplasma IgG antibodies. For Toxoplasma IgM and IgA antibodies, there is no reference method and their evaluation is done by comparing the results of one assay to those of another. There is a need for multiplexed assay platforms, as the serological diagnosis of T. gondii infection does not rely on the detection of a single Ig subtype. Here we describe the development of a plasmonic gold chip with vast fluorescence enhancement in the near-infrared region for simultaneous detection of IgG, IgM, and IgA antibodies against T. gondii in an ∼1-μl serum or whole-blood sample. When 168 samples were tested on this platform, IgG antibody detection sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were all 100%. IgM antibody detection achieved 97.6% sensitivity and 96.9% specificity with a 90.9% PPV and a 99.2% NPV. Thus, the nanoscience-based plasmonic gold platform enables a high-performance, low-cost, multiplexed assay requiring ultrasmall blood volumes, paving the way for the implementation of universal screening for toxoplasmosis infection during gestation.

Assessment of the IgA immunosorbent agglutination assay for the diagnosis of congenital toxoplasmosis on a series of 145 toxoplasmic seroconversions

A retrospective analysis of 145 medical records from our teaching hospital laboratory showed an overall specificity of greater than 97% for the IgA immunosorbent agglutination assay (ISAGA A) performed on the sera of babies to diagnose congenital toxoplasmosis (CT). These actualized data emphasize the ability of this test to confirm a diagnosis of congenital toxoplasmosis.

Assessment of the value of detecting specific IgA antibodies for the diagnosis of a recently acquired primary Toxoplasma infection

OBJECTIVE

To assess the value of detecting IgA antibodies for the diagnosis of a recently acquired primary Toxoplasma infection.

METHODS

IgA antibodies were screened in sera from 87 women with different serological profiles of Toxoplasma gondii IgM and IgG antibodies and Toxoplasma-specific IgG avidity. The IgM and IgG antibodies and the IgG avidity were measured with an automated Vitek Immuno Diagnostic Assay System (VIDAS). Anti-T.gondii IgA was measured with Platelia Toxo IgA TMB kits.

RESULTS

All 12 sera obtained from women with clinical and/or serological evidence of a recently acquired Toxoplasma infection were positive for IgA. In 42 serum samples obtained more than 6 months after T. gondii infection from women with no clinical evidence of infection, but who had a positive IgM test and a high IgG avidity index, the IgA-enzyme linked immunosorbent assay (ELISA) test results were positive, negative, and doubtful in 16 (38.1%), 23 (54.8%), and 3 (7.1%) sera, respectively. In eight women, IgA was detected in sera collected more than 9 months after the onset of infection. The IgA test result was also positive in 11 of 12 sera (91.7%) obtained from women with no clinical evidence of toxoplasmosis, but who had a positive IgM test and a borderline IgG avidity index. The IgA-ELISA was negative in 21 sera obtained more than 2 years after the onset of T. gondii infection from women with no clinical evidence of toxoplasmosis, but who had a negative IgM test and a positive IgG test.

CONCLUSION

These results show that IgA is not a dependable marker for a recently acquired primary Toxoplasma infection.

Toxoplasma gondii infection in pregnancy: opportunities and pitfalls of serological diagnosis

Because of its life cycle, the recovery of Toxoplasma gondii from biological samples is often impracticable. Consequently, a serological diagnosis represents the first and the most widely used approach to defining the stage of infection. The detection of IgG, IgM, IgA, IgE and IgG avidity by different methods offers this opportunity. However, the results may be affected by difficulties in interpretation, as the same antibody pattern may have a different valency, contingent upon subjects and clinical settings, e.g., pregnant women vs. neonates, and treated vs. untreated patients. This review describes the various factors that should be taken into account when performing serological tests for T. gondii, as well as the pitfalls that may be encountered during the interpretative process.

Evaluation of a commercial IgE ELISA in comparison with IgA and IgM ELISAs, IgG avidity assay and complement fixation for the diagnosis of acute toxoplasmosis

A panel of sera from patients with known case histories representative of acute toxoplasmosis (primarily lymphadenopathy, n = 106), latent toxoplasmosis (asymptomatic, n = 368) and negative samples (n = 54) was used to evaluate the capacity of five serological tests to differentiate among patients with acute or latent toxoplasmosis and non-infected individuals. Positive IgA, IgE and IgM ELISA results and low IgG avidity and complement fixation test (CFT) titres of >or=256 were considered to be indicative of acute toxoplasmosis. The most sensitive methods were IgM ELISA (98.1%) and CFT (97.1%), albeit with low specificity (65.0% and 64.5%, respectively) and positive predictive values (43.3% and 42.7%, respectively). IgG avidity assay and IgE ELISA had the highest specificity (97.7% and 91.7%, respectively) and the highest positive predictive values (89.4% and 75.6%, respectively). The best association between serological results and clinical findings was obtained with IgE ELISA (86%, as expressed via Youden's index). In a subset of 259 samples categorised by the period between the onset of clinical symptoms and sampling, >50% of patients had enlarged lymph nodes for <4 months, despite a broad range of differences. However, IgM remained positive for 12-18 months, IgA for 6-9 months and IgE for 4-6 months. IgG avidity remained low for a maximum of 4 months, after which avidity increased despite the persistence of enlarged lymph nodes and a positive IgE assay. Detection of IgE appears to be a highly specific test for confirming the acute nature of Toxoplasma infections that have been detected by other sensitive methods.

Detecção de imunoglobulinas IgG, IgM e IgA anti-Toxoplasma gondii no soro, líquor e saliva de pacientes com síndrome da imunodeficiência adquirida e neurotoxoplasmose

Estudamos 55 pacientes com sindrome da imunodeficiência adquirida (SIDA) e neurotoxoplasmose (grupo 1); 37 pacientes com SIDA e comprometimento neurológico por outra etiologia (grupo 2) e 18 indivíduos anti-HIV negativos com manifestações neurológicas (grupo 3), pesquisando IgG, IgA e IgM anti-Toxoplasma gondii, no soro, líquor e saliva, utilizando teste ELISA, para fins diagnósticos. O valor preditivo negativo do teste para o encontro de IgG no soro foi 100% e no líquor, 92,4%. Não houve diferença entre os três grupos quanto aos anticorpos IgA neste material. Para IgA, no líquor, o teste alcançou 72,7% de especificidade (p<0,05). Na saliva, apenas o encontro de IgG mostrou correlação com o diagnóstico de neurotoxoplasmose. Enfatizamos que a ausência de anticorpos IgG anti-T. gondii no soro e líquor depõe fortemente contra o diagnóstico de neurotoxoplasmose e que imunoglobulinas IgA específicas no líquor e IgG na saliva podem representar dois marcadores auxiliares para o diagnóstico diferencial da encefalite toxoplásmica na SIDA.

Strategy for diagnosis of congenital toxoplasmosis: evaluation of methods comparing mothers and newborns and standard methods for postnatal detection of immunoglobulin G, M, and A antibodies

In a study involving 14 laboratories supported by the European Community Biomed 2 program, we evaluated immunologic methods for the postnatal diagnosis of congenital toxoplasmosis (CT). Among babies born to mothers who seroconverted to positivity for toxoplasmosis during pregnancy, we analyzed 55 babies with CT on the basis of persistent anti-Toxoplasma immunoglobulin G (IgG) at 1 year of life and 50 control babies without anti-Toxoplasma IgG at 1 year of life in the absence of curative treatment with pyrimethamine-sulfonamides. We tested in-house methods such as the enzyme-linked immunofiltration assay (ELIFA) or Immunoblotting (IB) for the detection of IgG or IgM; these methods allowed comparison of the immunologic profiles of the mothers and the infants. We compared ELIFA and IB with a commercial enzyme immunoassay (EIA) or in-house immunosorbent agglutination assay (ISAGA) for the detection of IgM or IgA. The performances of combinations of methods were also assessed. A cumulative sensitivity of 98% during a 1-year follow-up was obtained with the ELIFA plus ISAGA combination. Only one case of CT was missed by the ELIFA plus ISAGA combination, whereas three cases were missed by the IB plus ISAGA combination, even though 48% of patients with CT were treated with pyrimethamine-sulfonamides, which are known to inhibit antibody neosynthesis. A similar performance was obtained with either ELIFA or IB in combination with EIA. The difference in performance between ELIFA plus ISAGA and IB plus ISAGA was not statistically significant (P = 0.31), and we conclude that both combinations of tests can be used for the diagnosis of CT in newborns.

Padronização de ensaio imunoenzimático para pesquisa de anticorpos das classes IgM e IgG anti-Toxoplasma gondii e comparação com a técnica de imunofluorescência indireta

A sorologia tem sido o método de escolha para o diagnóstico da toxoplasmose. Devido a isto, padronizamos um ensaio imunoenzimático (ELISA) e comparamos seus resultados com a técnica de imunofluorescência indireta (IFI). A técnica padronizada apresentou na pesquisa de IgG sensibilidade (S) de 96,7% e especificidade (E) de 75%, com valor de predição de positividade (VPP) de 83,3% e de negatividade (VPN) de 94,7%, com uma concordância ajustada (K) de 73,5%. A IFI apresentou S de 83,8%, E de 79,1% com VPP de 83,8 % e VPN de 79,1% com K de 63%. A concordância bruta entre os dois testes (ELISA/IFI) foi de 88,3% para pesquisa de IgG e de 81,5% para pesquisa de IgM, sendo o K de 70,8% para IgG e de 1,3% para IgM, sendo o índice de correlação (r) de 0,556 para IgG e de -0,023 para IgM. Podemos concluir que a ELISA-IgG padronizada é indicada nos processos de triagem sorológica, sendo a ELISA-IgM desaconselhada uma vez que apresentou baixos índices de concordância ajustada com a técnica de referência, sugerindo pouca confiabilidade dos resultados.

Do IgA, IgE, and IgG avidity tests have any value in the diagnosis of toxoplasma infection in pregnancy?

AIM

To determine the value of tests for specific IgA, IgE, and IgG avidity in diagnosing Toxoplasma gondii infection during pregnancy.

METHODS

In a retrospective study, current serological tests (dye test and three IgM assays with different sensitivities) were compared with immunosorbent agglutination assays (ISAGA) for specific IgA and IgE and an IgG avidity enzyme linked immunosorbent assay (ELISA). Patient group 1 comprised six women with definite or probable infection during pregnancy determined by congenital toxoplasmosis or laboratory results. Group 2 comprised seven women infected during or before 11 pregnancies (two consecutive pregnancies in two patients and three in a third).

RESULTS

One patient in group 1 seroconverted during pregnancy. IgA ISAGA and avidity confirmed acute infection when confirmatory IgM ELISA remained negative. In five of six patients from group 1, IgA and IgE ISAGA and avidity confirmed acute infection. In group 2, the dye test titre was raised in seven of 11 pregnancies (six of seven patients). Specific IgM and IgA were positive during all 11 pregnancies. IgE ISAGA was positive in only four of 11 pregnancies (three of seven patients), but negative results in the remainder may exclude acute infection. High avidity antibodies indicative of past infection were found in four of 11 pregnancies (two of seven patients).

CONCLUSIONS

Each test improved diagnosis or timing of infection but no single test was ideal. The IgA ISAGA was sensitive and detected seroconversion. Positive IgE ISAGA and low avidity both confirmed infection, whereas negative IgE may exclude acute infection. High avidity diagnosed past infection but persistence of low avidity reduced its value to differentiate acute and past infection. Further studies with larger patient groups are needed to determine the optimum diagnostic strategy. These techniques are valuable in complementing existing tests.

The investigation of toxoplasma infection associated with pregnancy

An audit was undertaken to determine case compliance with prenatal testing and investigation of infants for toxoplasma infection. Subsequently, the effect of enhanced reference unit Intervention was studied. The proportion of cases of toxoplasma infection associated with pregnancy completing an investigation programme was calculated. The effect of continued and short-term additional intervention was assessed and reasons for failure to comply were sought. The status of the child was established in 30% of cases when acute maternal toxoplasma infection was detected. Continuous reference unit intervention significantly improved case compliance to 45% over a 3-year period, but the effect was lost when the additional measures were withdrawn. Failure to complete the investigation procedure was associated with loss of patient-clinician contact and clinician/laboratory error. Enhanced intervention did not result in a significant improvement in compliance with the investigation programme for babies with clinical abnormality. The benefits of testing for toxoplasma infection associated with pregnancy are limited by failure to complete necessary investigations.

Value of detecting immunoglobulin E antibodies for the serological diagnosis of Toxoplasma gondii infection

The presence of immunoglobulin E (IgE) antibodies was determined by using the immunosorbent-agglutination assay (ISAGA) with 611 serum samples from patients with different clinical conditions to evaluate its value for the serodiagnosis of acute Toxoplasma gondii infection. By analyzing 43 consecutively drawn serum samples from 10 pregnant women who seroconverted, we could show that specific IgE antibodies seem to appear early after infection and are usually present for less than 3 to 5 months. Therefore, we assumed that IgE antibodies seem to be detectable only during the acute or reactivated stage of infection. According to our studies, the IgE ISAGA has an overall sensitivity of only 79.5%, but a specificity of 98.0%, with positive and negative predictive values of 95.5 and 89.8%, respectively. Detection of IgE antibodies in immunosuppressed patients with reactivation of latent T. gondii infection correlates with disease activity. Despite these encouraging results, one must note that IgE antibodies were not detectable in 4 of 14 patients with very recent infection proven by seroconversion. Therefore, detection of IgE antibodies seems to correlate with early acute or reactivated toxoplasmosis, whereas negative IgE results do not exclude the possibility of the acute stage of toxoplasmosis.

Detection of anti-toxoplasma immunoglobulin A antibodies by Platelia-Toxo IgA directed against P30 and by IMx Toxo IgA for diagnosis of acquired and congenital toxoplasmosis

Platelia-Toxo IgA and IMx Toxo IgA assays were used with 260 serum samples, of which 93 were from seroconverted patients, 58 were from 21 congenitally infected children, and 109 were from uninfected patients, to detect anti-P30 immunoglobulin A antibodies. Because of its enhanced sensitivity, Platelia-Toxo IgA is more efficient in diagnosing acute or congenital toxoplasmosis. IMx Toxo IgA must not be used to diagnose congenital toxoplasmosis.

Value of specific immunoglobulin A detection by two immunocapture assays in the diagnosis of toxoplasmosis

The diagnosis of Toxoplasma gondii infection is currently based on immunological tests, but tests for IgG and IgM antibodies alone are often insufficient to assess the risk of active disease, especially during pregnancy and in immunodeficient subjects. The supplementary diagnostic value of testing for antitoxoplasmic IgA in cases of acute, chronic, congenital and reactivated toxoplasmosis, relative to classical immunological tests, was evaluated using two immunocapture tests, one based on tachyzoite agglutination and the other on an immunoenzymatic complex recognizing the membrane protein P30 of Toxoplasma gondii. A total of 4,541 sera from 395 uninfected subjects, 468 immunized subjects with chronic infection, 117 subjects with acute infection and 403 children, 103 of whom had congenital toxoplasmosis, was tested. Specific IgA tests were negative in the nonimmune population, but tests for this immunoglobulin subtype became positive very rapidly during primary infection, and IgA disappeared more rapidly than IgM. In the children infected in utero, specific IgA was detected more frequently than IgM. In contrast, in a population of HIV-seropositive subjects with clinical toxoplasmosis, tests for IgA were poorly sensitive. The two tests for specific IgA produced similar results, except in the early stages of primary infection, in which immunoenzymatic testing for anti-P30 IgA was less sensitive than the agglutination method.