Immunoglobulin G and immunoglobulin M enzyme-linked immunosorbent assays and defined toxoplasmosis serological patterns

Radiation effects on Toxoplasma antigens: different immune responses of irradiated intact tachyzoites or soluble antigens in experimental mice models

Purpose: Purpose: Protein irradiation causes aggregation, chain breakage, and oxidation, enhancing its uptake by antigen-presenting cells. To evaluate if irradiated proteins participate on the protection, we studied the immune response induced in mice immunized with irradiated soluble extracts of T. gondii tachyzoites (STag) or irradiated intact T. gondii RH tachyzoites (RH^0.25 kGy).Material and Methods: Soluble extracts of Toxoplasma gondii tachyzoites (STag) were irradiated at different dose by Cobalt-60 source. By polyacrylamide gel electrophoresis (SDS-Page) we evaluated the effects on primary structures of protein STags induced by irradiation. By Enzyme-linked Immunosorbent Assay (ELISA) we evaluated the difference between humoral immune response induced by irradiated STag or RH tachyzoites in immunized mice from the detection of specific immunoglobulin G (IgG) antibodies in the serum of immunized mice. From challenge with viable RH strain of T. gondii we evaluated the protection induced in the immunized animals. By cytometry we performed the phenotyping of T and B lymphocytes in the peripheral blood of the immunized animals.Results: Irradiation dose of 1.5 kGy induced minimal changes in most proteins, without affecting their antigenicity or immunogenicity. Immunization showed saturation at the dose of 10 µg/mice, with worst response at higher doses. STag irradiated at 1.5  kGy (STag^1.5 kGy) induced higher survival and protection similar to T. gondii RH strain irradiated at 0.25 kGy (RH^0.25 kGy), with higher serum levels of high affinity IgG compared to STag native. Blood immune memory cells of mice immunized with STag^1.5 kGy had higher proportions of CD19⁺ (cluster of differentiation 19) and CD4⁺ (cluster of differentiation 14) cells, whereas mice RH^0.25 kGy had high proportion of memory CD8⁺ (cluster of differentiation 8) cells.Conclusions: Our data suggest that major histocompatibility complex type I (MHCI) pathway, appears seem to be used by RH^0.25 kGy to generate cytotoxic cells while STag1.5 kGy uses a major histocompatibility complex type II (MHCII) pathway for B-cell memory, but both induce sufficient immune response for protection in mice without any adjuvant. Irradiation of soluble protein extracts enhances their immune response, allowing similar protection against T. gondii in mice as compared to irradiated intact parasites.

CD39 and immune regulation in a chronic helminth infection: The puzzling case of Mansonella ozzardi

Background

Chronic helminth infections typically induce an immunoregulatory environment, with markedly reduced immune responses to both parasite-specific and unrelated bystander antigens. Here we tested whether these changes are also observed in human infections with Mansonella ozzardi, a neglected filarial nematode widely distributed across Latin America.

Methods

CD4⁺ T cell populations from microfilaremic (Fil+) and uninfected (Fil-) inhabitants in M. ozzardi-endemic riverine communities in Brazil were characterized by flow cytometry analysis. Plasma concentrations of a wide range of cytokines and chemokines were measured. We examined whether M. ozzardi infection is associated with suppressed in vitro lymphoproliferative and inflammatory cytokine responses upon stimulation with filarial antigen, unrelated antigens or mitogens.

Principal findings/Conclusions

Fil+ subjects had lower plasma levels of selected inflammatory cytokines, such as TNF-α, IL-8, and IL-6, than their Fil- counterparts. However, we found no evidence for attenuated T-cell responses to filarial antigens or co-endemic pathogens, such as malaria parasites and Toxoplasma gondii. CD4⁺ T cells expressing CD39, an ectonucleosidase involved in the generation of the anti-inflammatory molecule adenosine, were increased in frequency in Fil+ subjects, compared to uninfected controls. Significantly, such an expansion was directly proportional to microfilarial loads. Surprisingly, CD39 blocking with a neutralizing antibody suppressed antigen-driven lymphoproliferation in vitro, while decreasing inflammatory cytokine responses, in Fil+ and Fil- individuals. These findings suggest that circulating CD4⁺ CD39⁺ T cells comprise subsets with both regulatory and stimulatory roles that contribute to the immune homeostasis in chronic M. ozzardi infection.

Helminth infections downregulate immunity and reduce host’s inflammatory responses, but the filarial nematode Mansonella ozzardi, which is widely distributed across Latin America, appears to represent an exception to this rule. We found similar lymphoproliferative responses to filarial and unrelated antigens and comparable regulatory cytokine responses in subjects harboring M. ozzardi microfilariae, compared to local uninfected controls. The proportion of CD4⁺ T cell subtypes expressing CD39 was significantly increased in infected subjects and correlated positively with their microfilarial density. However, antibody blocking of CD39, an ectonucleosidase involved in the synthesis of the immunosuppresive molecule adenosine, paradoxically reduced, rather than promoted, antigen-driven lymphoproliferation in vitro. We suggest that CD39⁺ CD4⁺ T cells circulating in microfilaremics comprise both regulatory and stimulatory cell subsets that are concomitantly expanded. The balance between these cell subsets with opposing regulatory functions may be crucial to maintain immune homeostasis during chronic M. ozzardi infections.

CD19 LYMPHOCYTE PROLIFERATION INDUCED BY Bifidobacterium animalis subsp. lactis IN C57BL/6 MICE EXPERIMENTALLY INFECTED WITH Toxoplasma gondii

Toxoplasmosis is frequently acquired through the oral route by the ingestion of cysts or oocysts of Toxoplasma gondii. Once ingested, the parasites penetrate the intestinal epithelial cells and rapidly disseminate to all organs in the host. During T. gondii infection, the intestinal microbiota plays an important role in stimulating a protective immune response against the parasite. In this sense the use of probiotics is worthy of note since they are live microorganisms that have beneficial effects on the host through stimulation of the immune response that can be important in the control of T. gondii proliferation and dissemination in the host. In the present study, the action of the probiotic Bifidobacterium animalis subsp. lactis was investigated in C57BL/6 mice infected with oocysts of ME49 strain of T. gondii. The probiotic had an immunomodulatory action, inducing CD19 lymphocyte proliferation and consequently increasing anti-T. gondii antibody level.Bifidobacterium animalis subsp. lactisprovided protection in supplemented mice, compared to the control group. In addition, supplemented animals had milder inflammatory process in the small intestine, indicating that the probiotic protects the intestinal mucosa during infection with T. gondii. It was concluded that the probioticB. animalis subsp. lactis induces humoral immune response capable of providing protection against T. gondii infection.

Toxoplasma gondii Chitinase Induces Macrophage Activation

Toxoplasma gondii is an obligate intracellular protozoan parasite found worldwide that is able to chronically infect almost all vertebrate species, especially birds and mammalians. Chitinases are essential to various biological processes, and some pathogens rely on chitinases for successful parasitization. Here, we purified and characterized a chitinase from T. gondii. The enzyme, provisionally named Tg_chitinase, has a molecular mass of 13.7 kDa and exhibits a Km of 0.34 mM and a Vmax of 2.64. The optimal environmental conditions for enzymatic function were at pH 4.0 and 50 °C. Tg_chitinase was immunolocalized in the cytoplasm of highly virulent T. gondii RH strain tachyzoites, mainly at the apical extremity. Tg_chitinase induced macrophage activation as manifested by the production of high levels of pro-inflammatory cytokines, a pathogenic hallmark of T. gondii infection. In conclusion, to our knowledge, we describe for the first time a chitinase of T. gondii tachyzoites and provide evidence that this enzyme might influence the pathogenesis of T. gondii infection.

Serology using rROP2 antigen in the diagnostic of toxoplasmosis in pregnant women

Toxoplasma gondii causes severe fetal disease during acute infection in pregnant women, thus demanding early diagnosis for effective treatment and fetus preservation. Fetal tests are inefficient and risky, and diagnosis is based on maternal IgM serology, which had weak screening ability due to increased sensitivity, with alternative IgG avidity tests. Here, we performed ELISA and avidity assays using a recombinant T. gondii antigen, rROP2, in samples from 160 pregnant women screened from a large public hospital who were referred due to positive IgM assays. IgG serology and avidity assays were compared using whole T. gondii extract or rROP2. ELISA IgG detection with rROP2 showed good agreement with assays performed with T. gondii extract, but rROP2 IgG avidity assays were unrelated to whole extract antigen IgG avidity, regardless of the chaotrope used. These data show that avidity maturation is specific to individual antigen prevalence and immune response during infection. ELISA rROP2 IgG assays may be an alternative serological test for the diagnosis of toxoplasmosis during pregnancy, although our data do not support their use in avidity assays.

Reverse enzyme-linked immunosorbent assay using monoclonal antibodies against SAG1-related sequence, SAG2A, and p97 antigens from Toxoplasma gondii to detect specific immunoglobulin G (IgG), IgM, and IgA antibodies in human sera

The present study aimed to evaluate the performance of three monoclonal antibodies (MAbs) in reverse enzyme-linked immunosorbent assays (ELISAs) for detecting immunoglobulin G (IgG), IgM, and IgA antibodies against Toxoplasma gondii in 175 serum samples from patients at different stages of T. gondii infection, as defined by both serological and clinical criteria, as follows: recent (n = 45), transient (n = 40), and chronic (n = 55) infection as well as seronegative subjects (n = 35). The results were compared with those obtained by indirect ELISA using soluble Toxoplasma total antigen (STAg). Our data demonstrated that MAb A3A4 recognizes a conformational epitope in SAG1-related-sequence (SRS) antigens, while A4D12 and 1B8 recognize linear epitopes defined as SAG2A surface antigen and p97 cytoplasmatic antigen, respectively. Reverse ELISA for IgG with A3A4 or A4D12 MAbs was highly correlated with indirect ELISA for anti-STAg IgG, whereas only A4D12 reverse ELISA showed high correlation with indirect ELISA for IgM and IgA isotypes. To our knowledge, this is the first report analyzing the performance of a reverse ELISA for simultaneous detection of IgG, IgM, and IgA isotypes active toward native SAG2A, SRS, and p97 molecules from STAg, using a panel of human sera from patients with recent and chronic toxoplasmosis. Thus, reverse ELISA based on the capture of native SAG2A and SRS antigens of STAg by MAbs could be an additional approach for strengthening the helpfulness of serological tests assessing the stage of infection, particularly in combination with highly sensitive and specific assays that are frequently used nowadays for diagnosis of toxoplasmosis during pregnancy or congenital infection in newborns.

Immunization with MIC1 and MIC4 induces protective immunity against Toxoplasma gondii

Host cell invasion by Toxoplasma gondii is tightly coupled to the apical release of micronemal proteins (MIC). In this work, we evaluated the protective effect encountered in C57BL/6 mice immunized with MIC1 and MIC4 purified from soluble tachyzoite antigens by affinity to immobilized lactose. The immunized mice presented high serum levels of IgG1 and IgG2b specific antibodies. MIC1/4-stimulated spleen cells from immunized mice produced IL-2, IL-12, IFN-gamma, IL-10, but not IL-4, suggesting the induction of a polarized Th1 type immune response. When orally challenged with 40 cysts of the ME49 strain, the immunized mice had 68% fewer brain cysts than the control mice. Immunization was associated with 80% survival of the mice challenged with 80 cysts, contrasting with 100% mortality of the non-immunized mice in the acute phase. In this phase, there was much lower parasitism in the lungs and small intestine of the immunized mice, and they did not exhibit the early-stage signs of intestinal necrosis, which was clearly detected in the control mice. Our data demonstrate that MIC1 and MIC4 triggered a protective response against toxoplasmosis, and that these antigens are targets for the further development of a vaccine.

Toxoplasma gondii spreading in an urban area evaluated by seroprevalence in free-living cats and dogs

Infection by the protozoan parasite, Toxoplasma gondii is widely prevalent in humans and animals throughout the world. Transmission takes place mainly by ingestion of raw or undercooked meat that contains parasite cysts or by ingestion of oocysts excreted in cat faeces, which can contaminate water and raw vegetables. The incidence of toxoplasmosis in urban areas can thus be also related to environmental contamination with oocysts. A direct measure of this environmental contamination by oocyst counting is unfeasible for technical reasons. An interesting alternative for measuring T. gondii urban spreading is the seroprevalence in free-living urban animals, used as sentinels, once they are exposed to similar risks of Toxoplasma infection-like humans. With this aim, we tested serum samples from stray cats and dogs for antibodies to T. gondii by indirect haemagglutination assay (IHA) and enzyme-linked immunosorbent assay (ELISA). Antibodies to T. gondii were found in 40% (40 of 100) of the cats, less than the 50.5% (101 of 200) found in dogs by ELISA (P < 0.05). Haemagglutination showed low resolution and concordance, precluding their use for diagnosis of T. gondii infection compared with ELISA. The prevalence of T. gondii was lower among stray cats probably due to their selective alimentary habits and lower water and food intake. Toxoplasma gondii seroprevalence in stray dogs and cats could be an indirect indicator of the parasite spreading in urban areas.

Toxoplasma gondii and mast cell interactions in vivo and in vitro: experimental infection approaches in Calomys callosus (Rodentia, Cricetidae)

In the present work, we studied some qualitative and quantitative characteristics of mast cells located in the peritoneal cavity, submandibular and dorsal lymph nodes and ileum of Calomys callosus experimentally infected by Toxoplasma gondii. In uninfected animals, the majority of mast cells had similar ultra-structural characteristics, including several cytoplasmic granules with homogeneous and electron dense contents. However, after 1 h of infection, a significant influx of mast cells into peritoneal cavity was observed. The number of mast cells in this compartment decreased progressively in infected animals, and was significantly lower than the number of mast cells in control animals after 48 h of infection. Mast cells from infected animals or from purified suspensions that were infected in vitro presented significant morphological modifications, suggesting a degranulation process: cytoplasmic granules with electron dense content, fusion of the cytoplasmic granules, intracytoplasmic channels, cytoplasmic granules with flocculent material, plasma membrane rupture and granule contents in the extracellular environment. A remarkable increase in the influx of neutrophils toward the peritoneal cavity of the infected animals was observed after 12 h of infection. Moreover, this event occurred after the mast cell degranulation process took place. The relative increase in the number of mast cells and neutrophils was also followed by an increase in the number of macrophages, but there was a significant decrease in lymphocyte influx. After 48 h of infection, the parasite had spread from the peritoneal cavity to all organs examined. Also, mast cells from these organs showed evident morphological alterations, indicating the presence of the degranulation process. These results suggest that mast cells are deeply involved with the acute phase of the inflammatory response in this experimental model.

Heterologous antibodies to evaluate the kinetics of the humoral immune response in dogs experimentally infected with Toxoplasma gondii RH strain

An IgM capture ELISA using heterologous antibodies was developed to evaluate the kinetics of the humoral immune response in dogs experimentally infected with Toxoplasma gondii RH strain. Detection of parasite in tissues from inoculated dogs was evaluated by mouse bioassay and immunohistochemical techniques. Serum samples were obtained at regular intervals up to 62 days post-inoculation (p.i.), when the animals were necropsied and their tissues examined. Antibody levels were measured by IgM capture ELISA (McELISA), indirect hemagglutination (IHA), indirect fluorescent antibody test (IgG-IFAT) and indirect immunoenzymatic assay (IgG-ELISA). All dogs seroconverted but only one exhibited severe clinical signs of infection. IgM antibodies were detected by McELISA from the seventh day on, with decreasing IgM levels around the 27th day. Similar results were obtained from IHA, although McELISA showed earlier and longer detection of IgM antibodies. IgG antibodies were detected from the seventh day on, and throughout the period of observation. Immunohistochemical findings and mouse bioassay revealed the presence of free tachyzoites in tissues of the clinically affected dog only. These results suggest that T. gondii acute infection in dogs shows a remarkably transient IgM synthesis, and this feature may constitute an important marker of active infection. Furthermore, McELISA was shown to be a potential tool to diagnose canine toxoplasmosis.

200 Gy sterilised Toxoplasma gondii tachyzoites maintain metabolic functions and mammalian cell invasion, eliciting cellular immunity and cytokine response similar to natural infection in mice

200Gy gamma-irradiated Toxoplasma gondii RH tachyzoites failed to reproduce in vitro and in vivo. In short-term cultures, these parasites maintained a respiratory response, the ability to invade cells and preserved protein and nucleic acid synthesis. ELISA and Western blotting techniques demonstrated the similarity in humoral response between mice infected with gamma-irradiated tachyzoites and animals infected with naive parasites and treated with sulfadoxine, higher than mice immunised with formaldehyde-killed tachyzoites. Splenocyte stimulation by T. gondii antigen produced lymphoproliferative response and cytokine profile (IL-10, IL-12, IFN-gamma and TNF-alpha) similar to those produced by chronic natural infection. Mice immunised with irradiated tachyzoites had extended survival times after subsequent tachyzoite challenge, and displayed minimal cerebral pathology after cyst challenge. Irradiated tachyzoites lose their reproductive ability whilst maintaining metabolic function and may provide a novel tool for the study of toxoplasmosis and vaccine development.

Immunoglobulin M (IgM)-glycoinositolphospholipid enzyme-linked immunosorbent assay: an immunoenzymatic assay for discrimination between patients with acute toxoplasmosis and those with persistent parasite-specific IgM antibodies

In the present study we developed an enzyme-linked immunosorbent assay (ELISA) to measure immunoglobulin M (IgM) specific for glycoinositolphospholipids (GIPL) derived from tachyzoite membrane (IgM-GIPL ELISA). The sensitivity and specificity of the assay were compared with those of commercially available Toxoplasma-specific IgM serological tests, namely, immunofluorescence assay (IFA) with fixed tachyzoites and capture ELISA employing tachyzoite extracts. Our results show that all patients with acute toxoplasmosis, as determined by clinical data and conventional serological tests, were also positive by the IgM-GIPL ELISA. Interestingly, many patients that were classified as indeterminate, who had IgG with high avidity but positive results in the IgM-specific IFA and capture ELISA, were negative by the IgM-GIPL ELISA. Finally, we tested the sera from patients with rheumatoid arthritis and various parasitic infections and found no evidence of false positives in the IgM-GIPL ELISA.

Toxoplasma gondii micronemal protein MIC1 is a lactose-binding lectin

Host cell invasion by Toxoplasma gondii is a multistep process with one of the first steps being the apical release of micronemal proteins that interact with host receptors. We demonstrate here that micronemal protein 1 (MIC1) is a lactose-binding lectin. MIC1 and MIC4 were recovered in the lactose-eluted (Lac(+)) fraction on affinity chromatography on immobilized lactose of the soluble antigen fraction from tachyzoites of the virulent RH strain. MIC1 and MIC4 were both identified by N-terminal microsequencing. MIC4 was also identified by sequencing cDNA clones isolated from an expression library following screening with mouse polyclonal anti-60/70 kDa (Lac(+) proteins) serum. This antiserum localized the Lac(+) proteins on the apical region of T. gondii tachyzoites by confocal microscopy. The Lac(+) fraction induced hemagglutination (mainly type A human erythrocytes), which was inhibited by beta-galactosides (3 mM lactose and 12 mM galactose) but not by up to 100 mM melibiose (alpha-galactoside), fucose, mannose, or glucose or 0.2 mg/ml heparin. The lectin activity of the Lac(+) preparation was attributed to MIC1, because blotted MIC1, but not native MIC4, bound human erythrocyte type A and fetuin. The copurification of MIC1 and MIC4 may have been due to their association, as reported by others. These data suggest that MIC1 may act through its lectin activity during T. gondii infection.

Seroprevalence of Toxoplasma gondii infection in goats by the indirect haemagglutination, immunofluorescence and immunoenzymatic tests in the region of Uberlândia, Brazil

A comparative study of the indirect haemagglutination (IHA), immunofluorescence (IFAT) and immunoenzymatic (ELISA) tests was carried out to determine the prevalence of Toxoplasma gondii antibodies in goats. One hundred seventy-four serum samples were obtained from four goat herds from the region of Uberlândia, State of Minas Gerais. The distribution of the animals, according to their origin, was as follow: 71 from herd I; 39 from herd II; 37 from herd III; and 27 from herd IV. Serum samples were analyzed by IHA, IFAT and ELISA, considering the reactivity of the serum samples at dilution > or = 1:64 as cut off titer for the three tests. A global seroprevalence of 18.4% was observed, with significantly higher positivity rate in the herd II (66.7%) and older animals (> 36 months). A high and significant positive correlation was found between the titers obtained by the IHA versus IFAT, IHA versus ELISA, and ELISA versus IFAT. Therefore, it can be concluded that the three analyzed tests have shown to be highly concordant and appropriate for epidemiological surveys of Toxoplasma infection in goats. Although the seroprevalence of T. gondii infection in goats is relatively low in this region as compared to other regions of the country, adequate management might be useful and essential to control the infection in the goat herds.

The prevalence and avidity of Toxoplasma gondii IgG antibodies in pigs from Brazil and Peru

Raw or inadequately cooked pork is an important source of Toxoplasma gondii infection, and the infection rate in animals used as human food, is an important risk predictor. The prevalence of this infection was estimated in 396 sera from 5-month old pigs obtained at abattoirs in São Paulo, Brazil (300) and Lima, Peru (96). The seroprevalence was higher in pigs from Peru (32.3%) as compared to Brazil (9.6%), as detected by ELISA and Western blot. Hemagglutination gave poor resolution which was not useful for the diagnosis of T. gondii infection. Specific antibody avidity is correlated with infection time, as shown in experimentally infected piglets. Using an arbitrary cut-off of 50% avidity index, Brazilian pigs were found to be more recently infected than Peruvian pigs. Pork should be considered a significant source of human T. gondii infection both in Brazil and Peru. Avidity assays could help in the detection of the time of T. gondii infection in pigs, allowing preventive management.

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.

Detection of Toxoplasma gondii soluble antigen, SAG-1(p30), antibody and immune complex in the cerebrospinal fluid of HIV positive or negative individuals

Active infection by T. gondii was evaluated by immunoassay for soluble SAG-1 (p30), the major surface antigen from T. gondii, specific antibodies and immune complexes in human cerebrospinal fluid (CSF) samples. A total of 263 samples of CSF were collected from hospitalized patients presenting neurological disorders and analyzed for antibodies to HIV. Patients were divided into two groups: HIV positive (n = 96) or HIV negative (n =167). The results of the assays showed that 45% of all samples were positive for soluble SAG-1. Toxoplasma Ag/Ab immune complexes were detected in 19% of the CSF samples and 62% were positive for T. gondii- specific IgG. A combination of these assays in the presence of clinical findings consistent with active Toxoplasma infection may predict the presence of toxoplasmic encephalitis. Moreover, detection of soluble SAG-1 in the CSF of these individuals appears consistent with active infection.

Experimental infection of Calomys callosus (Rodentia, Cricetidae) by Toxoplasma gondii

Calomys callosus, Rengger 1830 (Rodentia, Cricetidae), a wild rodent found in Central Brazil, was studied to investigate its susceptibility to Toxoplasma gondii experimental infection and its humoral immune response against this protozoa. The electrophoretic profile of the serum proteins of C. callosus showed that IgG, which shows no affinity to Protein A, has higher cross reactivity with rat IgG than with IgG from other rodents. The susceptibility assay was performed by inoculation groups of animals with various suspensions of T. gondii tachyzoites from 10(2) to 10(6) parasites. All animals died between 3 and 9 days after infection and the kinetics of antibody synthesis was determined. Basically, they recognized predominantly the immunodominant antigen SAG-1 (P30). The immunohistochemistry assays revealed that the liver was the most heavily infected organ, followed by the spleen, lungs, intestine, brain and kidneys. It can be concluded that C. callosus is an excellent experimental model for acute phase of Toxoplasma infection.

Detection of Toxoplasma gondii-specific antibodies in dogs. A comparative study of immunoenzymatic, immunofluorescent and haemagglutination titers

We evaluated the titers of anti-T. gondii antibodies by various serological tests in 40 serum samples from dogs exhibiting clinical signs of infectious diseases. Indirect immunofluorescence (IgG-IFI), indirect haemagglutination (IHA and M-Toxo) and immunoenzymatic (ELISA and PA-ELISA) tests were carried out. Titers > or = 64 were considered as positive. Anti-Toxoplasma antibodies were found in 9 (22.5%), 14 (35%), 14 (35%) and 12 (30%) samples, respectively for IHA, IgG-IFI, ELISA and PA-ELISA. The results showed that 57% were negative in all tests and 43% of the dogs presented antibodies to T. gondii; from these, 20% were positive in all three tests with high titers of antibodies and 23% were positive in only one or two tests with low titers of antibodies and mainly related to the IFI and ELISA tests. We observed 5 (12.5%) and 1 (2.5%) reactive samples, respectively, by M-Toxo and IHA with or without 2-mercapthoethanol, in the attempt to detect specific IgM. We can conclude that serodiagnosis of toxoplasmosis in dog have to be based on the combination of serological tests (IFI and ELISA) and with emphasis at the determination of the titers and the classes of the specific antibodies.

Identification of Toxoplasma gondii antigens involved in the IgM and IgG indirect hemagglutination tests for the diagnosis of toxoplasmosis

Crude Toxoplasma gondii antigens represent raw material used to prepare reagents to be employed in different serologic tests for the diagnosis of toxoplasmosis, including the IgM and IgG indirect hemagglutination (IgG-HA and IgM-HA) tests. So far, the actual antigenic molecules of the parasite involved in the interaction with agglutinating anti-T. gondii antibodies in these tests are unknown. The absorption process of serum samples from toxoplasmosis patients with the IgG-HA reagent (G-toxo-HA) demonstrated that red cells from this reagent were coated with T. gondii antigens with Mr of 39, 35, 30, 27, 22 and 14 kDa. The immune-absorption process with the IgM-HA reagent (M-toxo-HA), in turn, provided antibody eluates which recognized antigenic bands of the parasite corresponding to Mr of 54, 35 and 30 kDa, implying that these antigens are coating red cells from this reagent. The identification of most relevant antigens for each type of HA reagent seems to be useful for the inspection of the raw antigenic material, as well as of reagent batches routinely produced. Moreover the present findings can be used to modify these reagents in order to improve the performance of HA tests for the diagnosis of toxoplasmosis.

Anti-Toxoplasma gondii immunoglobulins A and G in human saliva and serum

Paired human saliva and serum samples from 60 individuals were tested for specific IgA and IgG antibodies to Toxoplasma gondii. The study in both fluids was carried out by indirect immunoenzymatic assay (ELISA). Saline antigenic extract of T. gondii was used to coat plastic surfaces upon which the samples were then incubated; monospecific conjugates of anti-IgA and anti-IgG-peroxidase were then incubated with the samples after a washing procedure to separate the unbound antibodies. The enzymatic activity was measured and the results expressed in terms of ELISA index. Toxoplasma-specific IgG antibodies were detected in 43 of the serum samples (71.7%) and in 12 of the saliva samples (20.0%) whereas Toxoplasma-specific IgA antibodies were detected in 18 of the serum samples (30.0%) and in 12 of the saliva samples (20.0%). No association was observed when the Toxoplasma-specific IgG reactive and non-reactive serum samples were compared with the reactive and non-reactive saliva samples for this class of immunoglobulin. On the other hand, a significant association was observed when the Toxoplasma-specific IgA reactive and non-reactive serum samples were compared with the reactive and non-reactive saliva for this type of antibody. In conclusion, our results show that the detection of salivary IgA reflects the serum level of this isotype but salivary IgG does not. Moreover, the isolated detection of salivary IgG may not contribute to epidemiological studies of chronic toxoplasmic infections.

A monoclonal-based IgM capture ELISA for detection of antibodies to 22 and 41 kDa membrane antigens of Toxoplasma gondii

A murine monoclonal antibody which reacts to 22 and 41 kDa Toxoplasma gondii surface antigens was employed in an IgM capture enzyme-linked immunosorbent assay (ELISA). A total of 125 patients' sera were tested in the monoclonal-based assay. When compared with a commercial ELISA test (Abbott Toxo-M EIA) which uses polyclonal anti-T. gondii antibodies, good correlation (Pearsons coefficient r = 0.91) was observed. The specificity of the assay was studied by testing a panel of control sera obtained from healthy individuals and blood transfusion donors; all sera gave negative results. Serum samples positive for T. gondii antibodies were treated with 2-mercaptoethanol (2-ME) to demonstrate the specificity of the test for IgM antibodies. Reactivity of these sera was lost after the treatment. The test is not subject to interference by rheumatoid factor as sera positive for rheumatoid factor were negative in the assay. Reproducibility was good with the coefficients of variation for within-day tests below 10% and not exceeding 18% for day-to-day tests. The monoclonal-based assay is simple to perform and appears to be a viable test for diagnosis of T. gondii infection.

Evaluation of ELISA for the detection of Toxoplasma antibodies in swine sera

Enzyme-linked immunosorbent assay (ELISA) is compared with the indirect fluorescent antibody test (IFAT), the indirect haemagglutination test (IHAT) and the latex agglutination (LA) test for the detection of toxoplasma antibodies in swine sera. The 100 swine sera examined represent ELISA values from greater than 0 to 154 EIU. The agreement was highest (0.67) between ELISA and IFAT with an ELISA cut-off value of 30 EIU, and between ELISA and the LA test with an ELISA cut-off value of 50 EIU (0.74). All sera giving less than 10 EIU were negative in the other tests, and all those with greater than 70 EIU were positive in 1, 2 or all of the reference tests. In order to avoid false positive results with ELISA, all sera giving 10-70 EIU should be confirmed with a test which has a good specificity, e.g. IFAT. ELISA is a sensitive test and is highly suitable for the screening of large amounts of samples, but it may be too complicated for screening toxoplasma antibodies in the laboratories of abattoirs.

[Positive serology of syphilis, toxoplasmosis and Chagas' disease in pregnant women in their first visit to health centers in a metropolitan area, Brazil]

The diagnosis of some infectious diseases contracted during pregnancy is very important, as these diseases can be transmitted to the fetus. Four hundred and eighty-one pregnant women were studied, of an average 24.5 years of age (from 14 to 46), during their first prenatal visit to the State of S. Paulo's Health Care Centres in the subdistrict of Paz (Butantan), City of S. Paulo, Brazil, between April and October, 1988. Classified by trimester of pregnancy, 230 patients (47.8%) fell into the first, 203 (42.2%) into the second and 48 (10%) into the third trimester. Of the 474 patients that declared their income, 309 (65.2%) earned 1 MSPC (minimum salary per capita) per month, which gives some indication of the low socioeconomic status of our patients is. The serologic tests for syphilis, toxoplasmosis and Chagas' disease were analysed for each patient, more than one technique being used for each. The results were as follows: 25 patients (5.2%) had a positive test for syphilis; in 67 patients (13.9%) active toxoplasmosis was diagnosed (Presence of IgM antibodies in 6); 14 patients (2.9%) were positive for Chagas' disease, among which 10 (71.4%) came from the States of Bahia and Minas Gerais, where this disease has a high prevalence.

Evaluation of ELISA for the detection of Toxoplasma antibodies in swine sera

Enzyme-linked immunosorbent assay (ELISA) is compared with the indirect fluorescent antibody test (IFAT), the indirect haemagglutination test (IHAT) and the latex agglutination (LA) test for the detection of toxoplasma antibodies in swine sera. The 100 swine sera examined represent ELISA values from greater than 0 to 154 EIU. The agreement was highest (0.67) between ELISA and IFAT with an ELISA cut-off value of 30 EIU, and between ELISA and the LA test with an ELISA cut-off value of 50 EIU (0.74). All sera giving less than 10 EIU were negative in the other tests, and all those with greater than 70 EIU were positive in 1, 2 or all of the reference tests. In order to avoid false positive results with ELISA, all sera giving 10-70 EIU should be confirmed with a test which has a good specificity, e.g. IFAT. ELISA is a sensitive test and is highly suitable for the screening of large amounts of samples, but it may be too complicated for screening toxoplasma antibodies in the laboratories of abattoirs.

Assessment of immunoglobulin-M immunosorbent agglutination assay (ISAGA) for detecting toxoplasma specific IgM

An immunoglobulin-M immunosorbent agglutination assay (ISAGA) was introduced to detect toxoplasma specific IgM. This assay incorporates mu chain capture and use of entire toxoplasma trophozoites as an antigen source. The performance of the ISAGA was compared with that of a double sandwich enzyme linked immunosorbent assay (DS-ELISA) currently used in the Public Health Laboratory Service Toxoplasma Reference Laboratories. The ISAGA was found to be more sensitive than DS-ELISA but there was no demonstrable difference in the specificity or reproducibility between the two assays. The ISAGA is suitable for the diagnosis of acute toxoplasmosis in immunocompetent patients and as a screening test for recent infection in pregnant women. The persistence of ISAGA reactivity, however, is such that additional serological assessment is required to define the risk of congenital infection.

Toxoplasmosis serology: an efficient hemagglutination procedure to detect IgG and IgM antibodies

In search of an efficient but simple, low cost procedure for the serodiagnosis of Toxoplasmosis, especially suited for routine laboratories facing technical and budget limitations as in less developed countries, the diagnostic capability of Hematoxo, an hemagglutination test for toxoplasmosis, was evaluated in relation to a battery of tests including IgG- and IgM-immunofluorescence tests, hemagglutination and an IgM-capture enzymatic assay. Detecting a little as 5 I.U. of IgG antitoxoplasma antibodies, Hematoxo showed a straight agreement as to reactivity and non-reactivity for the 443 non-reactive and the 387 reactive serum samples, included in this study. In 23 cases presenting a serological pattern of acute toxoplasmosis and showing IgM antibodies, Hematoxo could detect IgM antibodies in 18, indicated by negativation or a significant decrease in titers as a result of treating samples with 2-mercapto-ethanol. However, a neat increase in sensitivity for IgM specific antibodies could be achieved by previously removing IgG from the sample, as demonstrated in a series of acute toxoplasmosis sera. A simple procedure was developed for this purpose, by reconstituting a lyophilized suspension of Protein A--rich Staphylococcus with the lowest serum dilution to be tested. Of low cost and easy to perform, Hematoxo affords not only a practical qualitative procedure for screening reactors and non-reactors, as in prenatal services, but also quantitative assays that permit to titrate antibodies as well as to identify IgM antibodies.

Annual change in immunoglobulin G and M antibody levels to Toxoplasma gondii in human sera

Sera collected from a Japanese population over 4 years at yearly intervals were examined for antibodies to Toxoplasma gondii by enzyme-linked immunosorbent assay (ELISA). Distributions of immunoglobulin (Ig) G antibody levels for 6 age groups consistently showed two antibody groups with constant mean ELISA values. Quantitative analysis of annual changes in IgG antibody levels for 1,366 pairs indicated increase of greater than or equal to 0.1 in 28 samples and decrease of greater than or equal to 0.1 in 58 samples, with the remaining 1,280 samples showing changes of less than 0.1. Mean ELISA values of samples with increase and decrease were 0.479 and 0.833, respectively, and the difference of 0.354 was similar to 0.412, that was the sum total of mean annual changes in samples with increase (0.228) and decrease (0.184). Increase of greater than or equal to 0.1 from the initial IgG antibody level of less than 0.1, which was considered as a serological evidence for newly acquired infection, was observed in 3 samples, but no increase was demonstrated in IgM antibody level. The changing pattern of IgG and IgM antibody levels in people during the initial and chronic phases of asymptomatic infections is discussed.

Protective immunity in toxoplasmosis: correlation between antibody response, brain cyst formation, T-cell activation, and survival in normal and B-cell-deficient mice bearing the H-2k haplotype

Correlations of Toxoplasma gondii-specific immunoglobulin M (IgM) and IgG production, antigen-specific T-cell activation, and the number of brain cysts were compared in immunocompetent CBA/J (H-2k), C3H/He (H-2k), and B-cell-deficient CBA/N (H-2k) mice. Almost all of the C3H/He mice (94%) survived in comparison to CBA/J (71%) and CBA/N (53%) mice following infection with 20 cysts of Me 49, an avirulent strain of T. gondii. The mortality in susceptible mice was reduced by treatment of the animals with sulfadiazine during the acute stage of infection. Decreased mortality in CBA/J and C3H/He mice as well as in B-cell-deficient mice was paralleled by formation of fewer brain cysts. The Toxoplasma-specific T-cell proliferation was markedly enhanced in all three strains at day 15 postinfection but not at day 45 postinfection when compared to animals not treated with the drug. In contrast, Toxoplasma-specific IgM and IgG levels were lower in CBA/J and CBA/N mice treated with sulfadiazine than in untreated mice of these strains. Although CBA/N mice developed almost no humoral response either with or without drug treatment, they produced fewer brain cysts than normal CBA/J mice. The results indicate a major role of cell-mediated immunity in protection against an acute Toxoplasma infection.

Ability of enzyme-linked immunosorbent assays to detect early immunoglobulin G antibodies to Toxoplasma gondii

Two ELISA procedures, one using sonicated antigen coated with carbonate buffer and the other formalin fixed trophozoites with dry coating, differ in their ability to detect early antibodies in toxoplasmosis. In order to identify factors responsible for this difference, seven ELISA systems differing from each other in antigen used and/or coating procedure were compared. Both fixation of the trophozoites with formalin and air-drying of the antigen in the microtiterplate were important factors determining the ability of the assay to detect IgG antibodies in the early stage of infection. Differences in the results of the two ELISA procedures can be used to distinguish between the acute and chronic stages of infection.

Interlaboratory evaluation of indirect enzyme-linked immunosorbent assay, antibody capture enzyme-linked immunosorbent assay, and immunoblotting for detection of immunoglobulin M antibodies to Toxoplasma gondii

One hundred and fifteen serum samples from healthy laboratory personnel and 50 consecutive samples from 19 patients with anamnestic clinical signs of toxoplasmosis were assayed by four laboratories for the presence of immunoglobulin M antibodies to Toxoplasma gondii by an indirect enzyme-linked immunosorbent assay (ELISA), an antibody capture assay with peroxidase-labeled toxoplasma antigen, and an immunoblotting assay. In addition, a commercially available antibody capture ELISA was used. Highly significant correlation coefficients were obtained between the four laboratories and the commercial test. The indirect ELISA and antibody capture ELISA showed equal sensitivity in detection of immunoglobulin M antibodies to toxoplasma in early-stage serum samples. However, in this study, the antibody capture assay discriminated better between serum samples obtained at early or late stages of toxoplasma infection.

Serodiagnosis of human G and M immunoglobulins to Toxoplasma gondii by ELISA using whole tachyzoites as antigens: a comparative study with the indirect haemagglutination (IHA) and immunofluorescence (IFA) tests

An indirect ELISA using whole tachyzoites of Toxoplasma gondii fixed onto the bottom of microtiter plate wells is described for detection of specific G and M anti-toxoplasma antibodies. ELISA results were compared with those of IFA and IHA tests. Similarity of antigens (cell surface) involved in ELISA and IFA permits high correlation between the two tests (r = 0.84-0.93, P less than 0.001) and results in good accordance for negative sera. As ELISA offers several advantages over the classical IFA test, it may be considered an alternative method for screening of G and M anti-toxoplasma antibodies.

An enzyme immunoassay for immunoglobulin M antibodies to Toxoplasma gondii which is not affected by rheumatoid factor or immunoglobulin G antibodies

An enzyme-linked immunosorbent assay (ELISA) for total antibodies to Toxoplasma gondii was modified to measure specific immunoglobulin M (IgM) antibodies. The assay requires three incubation periods totaling 2 h and enzyme-labeled-heavy-chain-specific antibodies to human IgM. The objective read-out in absorbance was normalized to percent of a standardized positive control for interpretations. No difference was observed between the assay results with or without previous absorption of the samples by Staphylococcus aureus protein A to remove most of the IgG antibodies. Addition of serum containing very high levels of IgG antibodies to another containing both IgG and IgM antibodies did not change the IgM assay values for the latter. None of the 22 sera containing high levels of IgM rheumatoid factor (RF) gave positive ELISA IgM results, even though 8 of them also had high levels of IgG toxoplasma antibodies. Mixtures of sera containing high concentrations of RF with sera having high levels of IgG toxoplasma antibodies also failed to show any false-positive reactions in the IgM toxoplasma assay. Thus, this ELISA for T. gondii IgM antibodies was not affected by IgG toxoplasma antibodies and RF.

[Research on IgM anti-Toxoplasma gondii antibodies by using a reverse immunoenzymatic technic]

Um teste imunoenzimático reverso foi padronizado utilizando-se como fase sólida, microplacas de polivinil sensibilizadas com anticorpos anti-IgM.7 Estas foram incubadas seqüencialmente com alíquotas de soros de pacientes com suspeita de toxoplasmose aguda, antígeno solúvel de Toxoplasma gondii, conjugado peroxidase F (ab')2 anti-toxoplasma e substrato enzimático. A atividade enzimática foi determinada por leitura espectrofotométrica, considerando-se como títulos dos soros a máxima diluição fornecendo valores de absorbância maiores que os obtidos com a menor diluição do soro padrão não-reativo. Em 69 amostras de soros de pacientes com toxoplasmose aguda, a média geométrica dos títulos no teste ELISA-Reverso IgM foi superior à de todos os outros testes para anticorpos IgM, não se observando resultados negativos falsos devidos a altos títulos de IgG específica. Não foi encontrada, também, reatividade cruzada em nenhuma das 104 amostras de soros de pacientes com outras patologias, inclusive em amostras contendo fator reumatóide IgM.

Serodiagnosis of toxoplasma infection using a purified parasite protein (P30)

The major surface protein (P30) of Toxoplasma gondii has been purified by immunoabsorption with anti-P30 monoclonal antibodies linked to a glutardialdehyde activated affinity absorbant. SDS-PAGE analysis of the eluted material followed by silver staining showed only a single band of 30,000 mol wt. Western blotting using antibodies from a rabbit immunized with purified P30 against the total Toxoplasma extract separated by SDS-PAGE again revealed an unique antigen of 30,000 daltons. The presence of repeated epitopes within P30 was confirmed by a two-site/one-antibody radiometric assay with the purified protein. Sandwich ELISA procedures with purified P30 clearly demonstrated that all 37 tested patients with acute toxoplasmosis presented significantly high levels of IgM anti-P30 antibodies. In addition, all 40 tested patients with chronic toxoplasma infection also showed high IgG anti-P30 antibody levels. These findings represent an essential step for the development of new reagents for the diagnosis of toxoplasmosis.

Use of a monoclonal antibody in a double-sandwich ELISA for detection of IgM antibodies to Toxoplasma gondii major surface protein (P30)

A double-sandwich ELISA, developed for detection of IgM antibodies to the major surface protein of Toxoplasma gondii (P30), is proposed for the diagnosis of acute acquired toxoplasmosis. The method is based on the capture of serum IgM antibodies, which are revealed indirectly by the sequential addition of a Toxoplasma extract and a beta-galactosidase-conjugated anti-P30 monoclonal antibody. All 57 patients tested with serological characteristics of recently acquired toxoplasmosis showed high levels of IgM anti-P30 antibodies. In addition, 5 out of the 24 patients with chronic toxoplasmosis and all 7 patients with a clinical acute infection in which the classical IgM serology was negative, also presented significant anti-P30 IgM antibodies. Patients with either rheumatoid factor or antinuclear antibodies were all negative. In view of its simplicity, specificity and sensitivity, this method is recommended for the current diagnosis of T. gondii infection.

Imunidade humoral e celular em indivíduos curados de leishmaniose visceral

Foi realizada avaliação imunológica em 48 indivíduos com históriapregressa de leishmaniose visceral (L. V)eem seis pacientes durante a fase aguda da doença e após o tratamento. Títulos significativos de anticorpos determinados pela técnica de imunofluorescência e/ou ELISA foram observados em 32 (67%) dos 48 casos. A avaliação da resposta imune humoral e celular nos seis pacientes durante a fase ativa da doença demonstrou títulos elevados de anticorpos (média 9536 ± 7169) e resposta línfoproliferativa ausente (323 ± 24). Após o tratamento (3 e 6 meses) os títulos de anticorpos só caíram em três dos seis pacientes, ao passo que linfócitos passaram a responder "in vítro" a antígenos de leíshmânía (11909 ± 5637). Estes dados demonstram que os indivíduos que adquirem leishmaniose visceral não são geneticamente incapacitados de responder a antígeno de leíshmânía equea persistência de títulos elevados de anticorpos anos após o tratamento, sugere que o parasita permaneça no hospedeiro após a cura clínica da doença.

Measurement of primary in vivo IgM- and IgG-antibody response to KLH in humans: implications of pre-immune IgM binding in antigen-specific ELISA

The antigen Keyhole Limpet Hemocyanin (KLH) is often used to test the primary in vivo antibody response capacity in humans. However, measurement of IgM anti-KLH antibodies in ELISA is complicated by the presence of natural antibodies in human serum. This problem occurs particularly at low antibody levels, i.e. after immunization with low doses of antigen and, under these conditions, it was found to be impossible to assess a dose-response curve by immunizing a series of individuals with different suboptimal doses of KLH. This problem was circumvented by choosing conditions for minimal binding of pre-immune IgM and to correct for such binding. Although signal-to-background ratios were markedly improved by modifying the ELISA conditions, pre-immune IgM still showed binding to KLH due to interaction with polysaccharide determinants. This non-specific binding was correlated with the total IgM content of the samples. When anti-KLH activities before and after immunization were expressed relative to total serum IgM, a significant correction was achieved, resulting in a diminished inter-individual variability with respect to both pre-immune and post-immunization values. As with IgG-class antibodies to KLH, virtually no binding was observed in pre-immune sera. After expression of the anti-KLH response as a ratio between the post-immunization and pre-immunization titres, a dose of 50 micrograms was found to be sufficient to evoke a detectable IgG-antibody response in the 10 subjects tested. To elicit a positive IgM response, a minimal dose of 250 micrograms was required.

Evaluation of an enzyme immunoassay for IgM antibodies to Treponema pallidum in syphilis in man

An enzyme immunoassay (EIA) for the detection of immunoglobulin M (IgM) antibodies to Treponema pallidum was investigated for specificity and sensitivity. Using the results in serum from 1192 patients with successfully treated syphilis, the assay was calculated to be about 97% specific. As in any other IgM enzyme linked immunosorbent assay (ELISA), rheumatoid factor played an important part in causing false positive results. Pre-absorption of serum with aggregated IgG was therefore necessary to perform the test. Evaluation of the results in serum from 385 patients with untreated primary, secondary, and latent syphilis as well as patients with untreated reinfections showed that the sensitivity of the assay depended on the stage of infection and varied between 98% and 93%. IgM antibody titres were about ten times higher in the EIA than in the indirect immunofluorescence assay using the IgM fractions of serum. From the results it may be concluded that the EIA is an appropriate technique not only for rapid and sensitive measurement of IgM antibodies in most patients with untreated syphilis but also for selecting treponemal IgM non-reactive patients.

Teste reverso para anticorpos igm na toxoplasmose, com hemácias sensibilizadas por antígenos de Toxoplasma gondii

Descreve-se um teste para anticorpos IgM-antitoxoplasma baseado na técnica de captura de IgM do soro por anticorpos anti-IgM adsorvidos a placas plásticas. Para evidenciação dos anticorpos antitoxoplasma nessa fração, utiliza-se uma suspensão de hemácias humanas, formolizadas e sensibilizadas por antígenos de Toxoplasma gondii. Nos testes positivos estas aparecem como uma camada contínua, enquanto que nos testes negativos depositam-se ao fundo das cavidades das placas. A leitura dos testes é muito mais evidente do que na técnica anteriormente proposta por Desmonts e cols, 1981, que utiliza suspensões de toxoplasmas. A suspensão de hemácias sensibilizadas pode ser preparada por simples diluição do reagente para o teste de hemaglutinação para a toxoplasmose.

Determination of IgG, IgM and IgA antibody responses in human toxoplasmosis by enzyme-linked immunosorbent assay (ELISA)

A 4-layer modification of ELISA for the determination of toxoplasma antibodies is described. In 103 Finnish blood donors 27 had antibodies against Toxoplasma gondii. One donor had IgM antibodies and IgA antibodies were found in 9. In patients with acute toxoplasmosis a vigorous IgG antibody response resulted in high antibody levels soon after infection, declining gradually to mean adult levels in approximately 2 yr. IgM antibodies appeared during the earliest phases of infection and disappeared as early as in 1 or 2 months in some cases and in most cases by the 6th month after infection. An IgA antibody response was also always seen. It was slower than the IgM response and could therefore be used to improve the laboratory diagnosis especially in cases where IgM antibodies had already disappeared and no further increase in IgG antibodies could be detected.

Characterization of Toxoplasma gondii antigens that react with human immunoglobulin M and immunoglobulin G antibodies

Studies were performed to define the nature of the Toxoplasma gondii antigens that are recognized by human immunoglobulin M (IgM) and IgG antibodies. Both IgM and IgG antibodies were found to be directed mainly against T. gondii membrane antigens in sera obtained from patients with acute toxoplasmosis. Treatment of the membrane preparation with DNase, RNase, or lipase had no apparent effect on the reactivity of the membrane antigens with IgM and IgG antibodies. Lipids isolated from tachyzoites were not recognized by either IgM or IgG antibodies. Exposure of T. gondii membranes to heat, proteolysis, or oxidation with sodium periodate decreased the reactivity of the membrane preparations with both IgM and IgG antibodies. A preparation of T. gondii proteins and polysaccharides were recognized by both immunoglobulin classes. T. gondii polysaccharides reacted with human IgG antibodies produced during both the acute and chronic phases of the infection. We concluded that, after infection with T. gondii, IgM and IgG antibodies are elicited in response to both protein and carbohydrate constituents of the invading parasite.

ELISA for specific anti-toxoplasma IgM antibodies: aspects related to serum interference

Two different methods were used to prepare solid-phase antigen (Ag) from soluble extracts of tachyzoites of Toxoplasma gondii: (A) physical adsorption on polystyrene beads; and (B) formaldehyde fixation of Ag previously dried in microtitration wells. In both cases a horseradish peroxidase conjugate with anti-IgM IgG was used as tracer. The assay scheme consisted of sequential incubations of diluted serum samples and tracer solution (1 or 2 h, 37 degrees C), colour development in the presence of substrate (10 min at room temperature), addition of H2SO4, and absorbance reading at 492 nm. In procedure A no cut-off value for positives could be determined owing to a large overlap between positive and negative sera. The extent of overlap directly correlated with the total IgM content of samples. With negative sera similar values were obtained with sensitized and untreated beads: thus a correction could be made by directly subtracting absorbance values determined in parallel runs with uncoated beads. Results with negative sera correlated with total IgM concentration in procedure B also, but much less variability of blank values allowed negative and positive sera to be effectively discriminated. A series of reference positive and negative sera was correctly classified by both procedures A and B. However, the latter appeared preferable, as not requiring blank correction.

Reproducible enzyme-linked immunosorbent assay with a magnetic processing system for diagnosis of toxoplasmosis

An enzyme-linked immunosorbent assay with polycarbonate-coated iron beads as the solid phase and with magnetic processing devices was evaluated for the quantitation of antibodies to Toxoplasma gondii in human serum samples. Under the parameters and other basic conditions determined in this study, the assay was highly reproducible: coefficients of variation for the absorbance values obtained with the positive serum were 2.42% in same-day tests and 3.75% in day-to-day tests. Significant correlations were observed between the present assay system and other conventional serological tests: correlation coefficients were 0.960 with the dye test and 0.929 with the latex agglutination test. Statistical analysis based on the frequency distribution of absorbance values for dye-test-positive and dye-test-negative serum samples gave feasible border lines for distinguishing between positive and doubtful samples (0.357) and between doubtful and negative samples (0.266). Under this diagnostic criterion, the results of our assay system agreed remarkably well with those obtained by the dye test and the latex agglutination test, with consistencies of 94.9 and 93.9%, respectively.

Comparison between ELISA and dye test for detection of naturally acquired toxoplasma gondii antibodies in the goat

Toxoplasma gondii IgG antibodies were measured in 212 goat sera, comparing the Sabin-Feldman dye-test and a three-layer sandwich enzyme-linked immunosorbent assay (ELISA). With 98 % concordance obtained between these 2 tests, the results are at the same paragon as for human sera. Accordingly, the ELISA sandwich procedure appears to be suitable for large-scale analysis of goat sera. The discordant 2 % were ELISA positive and dye-test negative. One possible explanation of the divergent titres is given using an immunized goat model.