Secretion of Toxoplasma gondii-specific antibody in vitro by peripheral blood mononuclear cells as a new marker of acute toxoplasmosis

Detection of Toxoplasma gondii bradyzoite genes in the peripheral blood mononuclear cells among patients with toxoplasmic chorioretinitis

BACKGROUND

Toxoplasmic chorioretinitis may occur as a result of acquired toxoplasmosis or reactivated congenital toxoplasmosis. In this study, Toxoplasma gondii bradyzoite genes along with the B1 gene were evaluated to detect T. gondii DNA in serum and peripheral blood mononuclear cells (PBMCs) of patients with toxoplasmic chorioretinitis.

METHODS

Blood samples were collected from 10 patients (7 cases of active chorioretinal lesions and 3 cases of old chorioretinal scars). The genomic DNA was extracted from the patients' serum and PBMCs and a polymerase chain reaction (PCR) assay was performed using bradyzoite genes along with B1. The subjects were also evaluated in terms of the T. gondii antibodies.

RESULTS

The PCR results were positive in four of seven patients (57.1%) with active ocular toxoplasmosis lesions. In three patients (42.8%), the PCR results were positive for MAG-1 and SAG-4 and in one patient (14.3%) the PCR results were only positive for the B1 gene. The PCR results were positive only in the PBMCs, whereas they were negative in the serum samples. Two patients with positive PCR results showed high Toxoplasma immunoglobulin G (IgG) antibody titres. However, none of the patients showed positive Toxoplasma IgM antibodies.

CONCLUSIONS

The PBMCs are suitable for evaluating toxoplasmic chorioretinitis. The present results showed that PCR with bradyzoite genes is useful in the diagnosis of toxoplasmic chorioretinitis in PBMCs.

An Overview of Peripheral Blood Mononuclear Cells as a Model for Immunological Research of Toxoplasma gondii and Other Apicomplexan Parasites

In biology, models are experimental systems meant to recreate aspects of diseases or human tissue with the goal of generating inferences and approximations that can contribute to the resolution of specific biological problems. Although there are many models for studying intracellular parasites, their data have produced critical contradictions, especially in immunological assays. Peripheral blood mononuclear cells (PBMCs) represent an attractive tissue source in pharmacogenomics and in molecular and immunologic studies, as these cells are easily collected from patients and can serve as sentinel tissue for monitoring physiological perturbations due to disease. However, these cells are a very sensitive model due to variables such as temperature, type of stimulus and time of collection as part of posterior processes. PBMCs have been used to study Toxoplasma gondii and other apicomplexan parasites. For instance, this model is frequently used in new therapies or vaccines that use peptides or recombinant proteins derived from the parasite. The immune response to T. gondii is highly variable, so it may be necessary to refine this cellular model. This mini review highlights the major approaches in which PBMCs are used as a model of study for T. gondii and other apicomplexan parasites. The variables related to this model have significant implications for data interpretation and conclusions related to host-parasite interaction.

Toxoplasma gondii: One Organism, Multiple Models

Toxoplasma gondii is an intensely studied protozoan parasite. It is also used as a model organism to research additional clinically relevant human and veterinary parasites due to ease of in vitro culture and genetic manipulation. Recently, it has been developed as a model of inflammatory bowel disease, due to their similar pathologies. However, researchers vary widely in how they use T. gondii, which makes study comparisons and interpretation difficult. The aim of this review is to provide researchers with a tool to: (i) determine the appropriateness of the different T. gondii models to their research, (ii) interpret results from the wide range of study conditions, and (iii) consider new advances in technology which could improve or refine their experimental setup.

Comparison of Toxoplasma gondii IgG avidity Architect and Vidas assays with the estimated date of infection in pregnant women

A maternal Toxoplasma gondii infection during pregnancy is a risk for congenital infection through maternal-fetal transplacental transmission. Estimation of the date of infection is of the utmost importance for management and treatment recommendations. In this setting, IgG avidity has been shown to be useful as high avidity rules out an infection dating less than 4 months. The estimated date of infection can also be obtained by the ratio of T. gondii IgG titers measured by the Vidas (bioMérieux) assay versus T. gondii IgG titers measured by the Architect (Abbott Laboratories) test, together with T. gondii IgM and IgA antibody responses. In this study, using 117 serum samples from pregnant women, we compared the IgG avidity values obtained by Architect and Vidas with the presumed date of T. gondii infection established by the T. gondii IgG ratio of IgG Vidas and IgG Architect plus the IgM and IgA results. To date, IgG avidity Vidas seems to exhibit better performance than Architect. For both assays, gray zone results were most likely obtained from patients infected more than 4 months before sampling. These data should be taken into account for a possible reconsideration of the interpretation of avidity results in the gray zone.

In utero and at birth diagnosis of congenital toxoplasmosis: use of likelihood ratios for clinical management

BACKGROUND

The results of the ante- and neonatal diagnostic tests for congenital toxoplasmosis influence the decision to treat the newborn immediately after birth. Here, we estimate the positive and negative likelihood ratios (LRs) and the probabilities of congenital infection according to PCR and IgM-IgA tests results.

METHODS

The study concerned 767 children born between 1996 and 2002 and followed-up for 1-year at Croix-Rousse hospital, Lyon, France. The LRs and the post-test probabilities were estimated conditionally on gestational age at maternal infection using a logistic regression approach.

RESULTS

For the PCR and the IgM-IgA tests, the positive LRs were high. In children with one positive test when only one test was done, the probability of infection reached 90% when the maternal infection occurred at 18-weeks gestation or later. This probability was close to 100% when the 2 tests were positive, whatever the gestational age. The negative LRs of the 2 tests moved closer to 0 at later gestational ages. However, when the tests were negative, the probability of infection remained greater or equal to 10%, except in early maternal infection. When the 2 tests were discordant, the probability of infection was about 50% in early maternal infection.

CONCLUSION

Providing reliable probabilities of congenital infection, the PCR and IgM-IgA tests guide clinical management and counseling of parents.

In vitro anti-Toxoplasma gondii antibody production by peripheral blood mononuclear cells in the diagnosis and the monitoring of toxoplasmic encephalitis in AIDS-related brain lesions

The spontaneous secretion in vitro of anti-Toxoplasma gondii antibodies by peripheral blood mononuclear cells was assessed in 69 patients with AIDS-related brain lesions. The sensitivity and specificity of this assay in the diagnosis of toxoplasmic encephalitis (TE) were found to be 85.4% and 92.8%, respectively. Twenty-four patients with TE were observed during 1-year follow-up after initiation of anti-Toxoplasma treatment and classified on the basis of their clinical and radiologic responses as sustained responders (SR; n = 11), incomplete responders (IR; n = 7) or transient responders (TR; n = 6). In vitro anti-T. gondii antibody secretion decreased as early as the first month after initiation of treatment and disappeared within the year in SRs, persisted in IRs, and decreased but rebounded at relapse in the TR patients. In vitro anti-T. gondii antibody, which reflects immune system activation by parasitic antigens, could be a surrogate marker of TE in AIDS patients.

Circulating Toxoplasma gondii-specific antibody-secreting cells in patients with congenital toxoplasmosis

Patients with congenital toxoplasmosis occasionally show rises in serum antibodies to Toxoplasma gondii (serological rebound), but the underlying cause remains unclear. The acute or chronic presence of available antigen often causes the appearance, in the peripheral blood, of cells actively secreting specific antibody. We have evaluated the capacity of circulating blood cells from 91 children born to T. gondii-infected mothers to actively synthesize anti-T. gondii antibodies according to their serological status. Supernatants from 7-day cultures of peripheral blood mononuclear cells were evaluated for antibody by cytofluorimetry. Only 1 of 49 subjects with low and stable serum antibody titers produced specific antibodies on cultures, while 9 of 22 subjects with recent rebound were positive. One of the positive children alone showed clinical signs of parasite activity. These observations suggest that rebound may be associated with production of available parasite antigens, possibly associated with reactivation. Differentiation from other causes, such as polyclonal B cell stimulation, would improve our ability to detect clinically significant reactivation and to prevent complications.

In-vitro synthesis of antibodies to Toxoplasma gondii by lymphocytes from HIV-1-infected patients

Toxoplasma-specific in-vitro antibody production by peripheral blood lymphocytes (PBL) was investigated in 124 adults infected with human immunodeficiency virus (HIV-1). PBL from 20 of 21 patients with cerebral toxoplasmosis showed spontaneous in-vitro secretion of antibodies to Toxoplasma gondii antigens. Among 103 HIV-1-infected patients without signs or symptoms of toxoplasmosis, PBL from 19 produced toxoplasma-specific antibodies in vitro; 5 of these patients, who discontinued prophylaxis for toxoplasmic encephalitis, showed in-vitro antibody production 3-15 months before the diagnosis of toxoplasmic encephalitis. In-vitro production of toxoplasma-specific antibodies could improve the diagnosis of toxoplasmic encephalitis in HIV-1-infected patients.

Cytomegalovirus-specific in vitro antibody production by peripheral blood lymphocytes from renal transplant recipients with CMV infection

Cytomegalovirus-specific in vitro antibody production (CMV-IVAP) by peripheral blood lymphocytes (PBL) was investigated in 12 renal transplant recipients. CMV-IVAP, CMV-serology, and viral cultures were carried out weekly during at least 8 weeks after transplantation. Nine episodes of CMV infection occurred in eight patients. CMV-IVAP was positive in eight episodes; IgG and/or IgA and/or IgM antibodies reacting with several CMV polypeptides were secreted by PBL. In two patients with primary CMV infection, only IgA antibodies were detected. Cytomegalovirus cultures were positive in eight episodes and serological evidence of CMV infection was obtained in five episodes. In one case, CMV-IVAP was observed before CMV isolation and in another case, before serological evidence of CMV infection. Our study indicates that CMV-IVAP could represent an additional tool for the diagnosis of CMV infection. Our study indicates that CMV-IVAP could represent an additional tool for the diagnosis of CMV infection in renal transplant recipients.