Toxoplasma gondii-specific IgG avidity testing in pregnant women

BACKGROUND

The parasite Toxoplasma gondii can cause congenital toxoplasmosis following primary infection in a pregnant woman. It is therefore important to distinguish between recent and past infection when both T. gondii-specific IgM and IgG are detected in a single serum in pregnant women. Toxoplasma gondii-specific IgG avidity testing is an essential tool to help to date the infection. However, interpretation of its results can be complex.

OBJECTIVES

To review the benefits and limitations of T. gondii-specific avidity testing in pregnant women, to help practitioners to interpret the results and adapt the patient management.

SOURCES

PubMed search with the keywords avidity, toxoplasmosis and Toxoplasma gondii for articles published from 1989 to 2019.

CONTENT

Toxoplasma gondii-specific IgG avidity testing remains a key tool for dating a T. gondii infection in immunocompetent pregnant women. Several commercial assays are available and display comparable performances. A high avidity result obtained on a first-trimester serum sample is indicative of a past infection, which occurred before pregnancy. To date, a low avidity result must still be considered as non-informative to date the infection, although some authors suggest that very low avidity results are highly suggestive of recent infections depending on the assay. Interpretation of low or grey zone avidity results on a first-trimester serum sample, as well as any avidity result on a second-trimester or third-trimester serum sample, is more complex and requires recourse to expert toxoplasmosis laboratories.

IMPLICATIONS

Although used for about 30 years, T. gondii-specific avidity testing has scarcely evolved. The same difficulties in interpretation have persisted over the years. Some authors have proposed additional thresholds to exclude an infection of <9 months, or in contrast to confirm a recent infection. Such thresholds would be of great interest to adapt management of pregnant women and avoid unnecessary treatment; however, they need confirmation and further studies.

Human herpes virus co-infection is associated with mortality in HIV-negative patients with Pneumocystis jirovecii pneumonia

The purpose of this investigation was to characterize the management and prognosis of severe Pneumocystis jirovecii pneumonia (PJP) in human immunodeficiency virus (HIV)-negative patients. An observational cohort study of HIV-negative adults with PJP documented by bronchoalveolar lavage (BAL) through Gomori-Grocott staining or immunofluorescence, admitted to one intensive care unit (ICU) for acute respiratory failure, was undertaken. From 1990 to 2010, 70 patients (24 females, 46 males) were included, with a mean age of 58.6 ± 18.3 years. The mean Simplified Acute Physiology Score (SAPS)-II was 36.9 ± 20.4. Underlying conditions included hematologic malignancies (n = 21), vasculitis (n = 13), and solid tumors (n = 13). Most patients were receiving systemic corticosteroids (n = 63) and cytotoxic drugs (n = 51). Not a single patient received trimethoprim-sulfamethoxazole as PJP prophylaxis. Endotracheal intubation (ETI) was required in 42 patients (60.0 %), including 38 with acute respiratory distress syndrome (ARDS). In-ICU mortality was 52.9 % overall, reaching 80.9 % and 86.8 %, respectively, for patients who required ETI and for patients with ARDS. In the univariate analysis, in-ICU mortality was associated with SAPS-II (p = 0.0131), ARDS (p < 0.0001), shock (p < 0.0001), and herpes simplex virus (HSV) or cytomegalovirus (CMV) on BAL (p = 0.0031). In the multivariate analysis, only ARDS was associated with in-ICU mortality (odds ratio [OR] 23.4 [4.5-121.9], p < 0.0001). PJP in non-HIV patients remains a serious disease with high in-hospital mortality. Pulmonary co-infection with HSV or CMV may contribute to fatal outcome.

Usefulness of immunoblotting and Goldmann-Witmer coefficient for biological diagnosis of toxoplasmic retinochoroiditis

Toxoplasmosis is a frequent cause of retinochoroiditis. Although the diagnosis relies mainly on ophthalmological examination, biological approaches are particularly useful in patients with atypical lesions. In a prospective study to determine the value of immunoblotting and immune load calculation in the diagnosis of active toxoplasmic retinochoroiditis, aqueous humor samples from 21 patients with retinochoroiditis and 5 control patients with cataracts were tested. Immune load was calculated on the basis of intraocular antibody production. The immune load ratio between aqueous humor and serum (Goldmann-Witmer coefficient) was significant (i.e. >2) in 9 of the 17 (53%) patients with retrospectively documented toxoplasmic retinochoroiditis. Immunoblotting suggested local antibody production in 10 of 17 (59%) patients. The combination of the two techniques gave a sensitivity of 71% (12/17). Both techniques were negative in the four patients in whom the final diagnosis of toxoplasmic retinochoroiditis was negative and in the five patients with cataracts. These results confirm the value of combining these two techniques. Moreover, immunoblotting has the advantages of being easy to perform and of requiring a very small sample.

Contribution of new techniques for the diagnosis of congenital toxoplasmosis

Congenital toxoplasmosis is still a concern, particularly in France, where the seroprevalence is high. For an efficient prevention program, reliable techniques are necessary. During the past ten years, biological advances have been made to improve the performance of antenatal diagnosis as well as the postnatal detection of infected neonates. In this review we will touch on three main points: 1) the dating of seroconversion during the course of pregnancy, 2) the value of antenatal diagnosis, 3) the new modalities for postnatal serological follow-up of newborns.

[Mitogen activated protein kinases (MAPK) and Toxoplasma gondii host cell invasion]

Toxoplasmosis is still a big concern in Public Health in France, regarding two particular aspects: congenital toxoplasmosis and reactivated toxoplasmosis in immunodeficient patients. Toxoplasma gondii is an obligate intracellular parasite, that can invade almost all nucleated cells. The invasion step has been widely studied, but its accurate mechanism and the cell receptor remain largely unknown. In this work, we have attempted to investigate the role of kinases and signal transduction in the host cell penetration. We characterized mitogen-activated protein kinases (MAPK). in the parasite itself by immunoblotting, immunofluorescence, and determination of enzymatic activity. In particular, we identified two proteins of 43 and 47 kDa, that could be homologues of extracellular signal-regulated kinases (ERK), i.e. ERK2 and ERK1, respectively. These parasite MAPK are activated by calcium and phorbolmyristyl acetate and inhibited by RO 31-8220, suggesting an activation through protein kinases C (PKC). Indeed the MAPK kinase (= MEK) inhibitor PD98059 inhibits the activation of parasite MAPK, suggesting that a MEK homologue could be responsible for the dual phosphorylation of MAPK on tyrosine and threonine residues, necessary for their activation. Finally, we demonstrated that activation or inhibition of parasite MAPK by preincubation of parasites with various activators or inhibitors led to an increased or reduced host cell invasion in vitro by parasites, respectively. All these results are in favour of a role of ERK-type parasite kinases in T. gondii infectivity in vitro.

Detection of tyrosine phosphorylated proteins in Trichinella spiralis L1 larvae

Western-blotting analysis showed the presence of tyrosine phosphorylated proteins in crude extracts of T. spiralis larvae and these phosphorylated proteins were located by immunofluorescence on the striations of the larval cuticle. The patterns of phosphorylated proteins were modified when larvae were incubated with bile.

Neosynthesized IgG detected by Western blotting in Toxoplasma-seropositive heart or lung transplant recipients

Toxoplasmosis is a life-threatening disease in heart- or lung transplant recipients that can result either from the reactivation of a latent infection or from an organ-transmitted infection. The diagnosis of acute toxoplasmosis is easy in cases of seroconversion following a mismatch. However, when the recipient is Toxoplasma-seropositive before transplantation, usual serological techniques do not allow the differentiation between endogenous and organ-related reinfection. The aim of this study was to determine whether western blotting could contribute to this differentiation. Sequential sera from two heart- and one liver- and lung transplant patients whose anti-Toxoplasma antibody titers strongly increased after transplantation, were analyzed by western blotting. Neosynthesized IgG were observed on blots incubated with the sera from two patients who had received transplants from Toxoplasma-seropositive donors, whereas no neosynthesized IgG was detected on blots from the patient who had received a transplant from a Toxoplasma-seronegative donor. Our results suggest that the detection of neosynthesized IgG in the recipient may be related to the recognition of a new parasite strain possibly brought by the transplant from a Toxoplasma-seropositive donor.

Lack of utility of specific immunoglobulin G antibody avidity for serodiagnosis of reactivated toxoplasmosis in immunocompromised patients

The avidities of Toxoplasma-specific immunoglobulin G serum antibodies were measured in immunocompromised patients presenting with cerebral or extracerebral toxoplasmosis and/or serological reactivation. Since avidity remained high and stable in 39 of 40 patients with toxoplasmosis and 27 of 28 patients with serological reactivation, we conclude that this test cannot help diagnose toxoplasmosis in these patients.

Biochemical characterization of mitogen-activated protein (MAP) kinase activity in Toxoplasma gondii

Mitogen-activated protein (MAP) kinase or extracellular signal-regulated kinase (ERK) are activated by many extracellular stimuli. In this study, we investigated whether MAP kinase and tyrosine kinases were involved in transducing signals in Toxoplasma gondii. Using anti-phosphotyrosine and anti-active ERK antibodies, we identified several phosphorylated proteins in Toxoplasma. In particular, phosphorylation of a 47 kDa and a 43 kDa protein increased strongly after calcium influx. MAP kinase activity, caused by calcium influx, was determined using either a specific synthetic peptide, or an in gel kinase assay. Conversely, calcium chelators (BAPTA and EGTA) and a calcium channel blocker (nifedipine) inhibited this activation. Also, a specific inhibitor of MAP kinase kinase (PD 098059) blocked MAP kinase activity. Three specific anti-MAP kinase antibodies recognized the 47 kDa and 43 kDa proteins, which were putatively identified as ERK1- and ERK2-homologs, respectively. These findings provide early evidence of signal transduction involving members of the MAP kinase family in T. gondii.

Involvement of the mitogen-activated protein (MAP) kinase signalling pathway in host cell invasion by Toxoplasma gondii

Little is known about signalling in Toxoplasma gondii, but it is likely that protein kinases might play a key role in the parasite proliferation, differentiation and probably invasion. We previously characterized Mitogen-Activated Protein (MAP) kinases in T. gondii lysates. In this study, cultured cells were tested for their susceptibility to Toxoplasma gondii infection after tachyzoite pretreatment with drugs interfering with MAP kinase activation pathways. Protein kinases inhibitors, i.e. genistein, RO31-8220 and PD098059, reduced tachyzoite infectivity by 38 +/- 4.5%, 85.5 +/- 9% and 56 +/- 10%, respectively. Conversely, protein kinases activators, i.e. bombesin and PMA, markedly increased infectivity (by 202 +/- 37% and 258 +/- 14%, respectively). These results suggest that signalling pathways involving PKC and MAP kinases play a role in host cell invasion by Toxoplasma.

Value of prenatal diagnosis and early postnatal diagnosis of congenital toxoplasmosis: retrospective study of 110 cases

We reviewed the files of 110 women with Toxoplasma seroconversion during pregnancy. Prenatal diagnosis was attempted for 94 women by amniotic fluid sampling. Toxoplasma gondii was detected by PCR, with or without tissue culture and mouse inoculation. The early neonatal diagnostic procedure included placental testing by PCR and/or mouse inoculation, cord blood serological testing, and comparison of maternal and newborn antibodies by Western blotting (WB). Serological follow-up of the infants was conducted during the first year of life or until the diagnosis of congenital toxoplasmosis (CT) could be ruled out. Congenital infection was diagnosed in 27 individuals (20 live births) in the prenatal and/or neonatal period. The sensitivity and specificity of prenatal diagnosis were 81 and 100%, respectively. Placental examination was positive for 66.7% of individuals with CT and was always negative for neonates without CT. Cord blood serology detected immunoglobulin M (IgM) and/or IgA in 80% of infected newborns, with respective specificities of 91.2 and 87.7%. By WB we detected bands on IgG and IgM blots recognized by the newborn serum but not by the maternal serum (neosynthesized IgG and/or IgM) for 88.2% of infected infants within the first 2 months of life with a specificity of 100%. Early postnatal diagnosis was negative for 2 of the 20 neonates with CT. Both of these newborns had a negative prenatal diagnosis and were asymptomatic, suggesting a very low parasite load. In conclusion, despite the use of advanced methods, some cases of congenital toxoplasmosis cannot be detected early, which underlines the importance of careful follow-up of newborns who are at risk.

Synergistic effect of clindamycin and atovaquone in acute murine toxoplasmosis

The effect of clindamycin (CLI) combined with autovaquone (ATO) was examined in a murine model of acute toxoplasmosis. Swiss Webster mice intraperitoneally infected with 10(2) or 10(4) tachyzoites of the RH strain of Toxoplasma gondii were perorally treated with either drug alone (for ATO, 5, 25, 50, or 100 mg/kg of body weight/day; for CLI, 25, 50, or 400 mg/kg/day) or both combined (for ATO plus CLI, respectively, 5 plus 25, 25 plus 25, 25 plus 50, 50 plus 50, or 100 plus 400 mg/kg/day) starting with day 1 for 14 days. Survival was monitored during 7 weeks. Residual infection was assessed by a bioassay of representative 4-week survivors and by parasite DNA detection by PCR for representative 7-week survivors. An effect of treatment was shown in all treatment groups compared to untreated control mice (P = 0.0000). Among mice infected with 10(2) parasites, ATO and CLI at any dose combination protected significantly more animals than ATO alone (P = 0.0000), but compared to CLI alone, given its good effect, the combined drugs were no more effective (P > 0.05). For mice infected with 10(4) parasites, the drugs combined at the lowest and highest doses (5 plus 25 and 100 plus 400 mg/kg/day) were, similarly, more effective than ATO alone (P = 0.035 and 0.000, respectively) but not than CLI alone (P > 0. 05). However, treatment with ATO plus CLI at 25 plus 25, 25 plus 50, and 50 plus 50 mg/kg/day protected 20, 33, and 78% of mice, respectively, compared to virtually no survivals among those treated with either drug alone (P < 0.0005), thus demonstrating a significant synergistic effect of ATO and CLI against T. gondii. Furthermore, the dose of ATO at a given dose of CLI was shown to be critical to the effect. Moreover, the absence of residual infection in some survivors shows the potential of this drug combination to eliminate the parasite.

Performance of a Western blot assay to compare mother and newborn anti-Toxoplasma antibodies for the early neonatal diagnosis of congenital toxoplasmosis

The aim of this study was to retrospectively evaluate the performance of a Western blot assay to compare mother and newborn anti-Toxoplasma gondii antibodies for the early neonatal diagnosis of congenital toxoplasmosis. Since specific anti-Toxoplasma IgM or IgA is detected inconstantly at birth in the neonate, the diagnosis of congenital toxoplasmosis is often delayed until 6-9 months, after IgG titers have been observed persistently. In this study, 81 paired samples from 60 mother/child pairs were tested for IgG and IgM patterns. All mothers had (or were strongly suspected to have) acquired toxoplasmosis during pregnancy. Specific IgM and IgA were simultaneously detected by immunocapture tests, and IgG was titrated. A serological and clinical follow-up of infants was conducted during the first year of life until the diagnosis of congenital toxoplasmosis could be either confirmed or ruled out. Seventeen of the 60 newborns were congenitally infected. Specific IgM or IgA was detected by immunocapture at birth in 76.5% and 70.6% of cord sera from infected neonates, respectively, with an equal specificity of 77.5%. Comparative Western blot allowed the detection of neosynthesized IgG and IgM in the cord blood of 50% and 78.6% of infected infants, respectively, with a specificity of 100%. The combination of IgA and IgM immunocapture tests, the analysis of IgG and IgM Western blot patterns, and the combination of both techniques allowed the detection of 94%, 94%, and 100% of cases within the first 3 months of life, respectively. In conclusion, Western blotting seems to be a useful complementary tool for the early postnatal diagnosis of congenital toxoplasmosis.

[Comparative value of 2 western blot techniques for confirmation of hydatidosis diagnosis]

Serological diagnosis of hydatid disease can be performed using different techniques, including ELISA, indirect immunofluorescence (IFI), in-gel immunodiffusion, electrosyneresis (ES), complement fixation technique, hemagglutination, latex sensibilized agglutination. However, all these techniques can lead to discordant results, according to their sensitivity and specificity rates. There is therefore a need for a confirmation technique, which can be either an immuno-electrophoresis assay, or an immunoblot assay. In this study, we compared two Western-Blot (WB) assays: the QualiCode Hydatid disease kit (Immunetics, Cambridge, MA, USA) and an in-house technique. Eighteen sera were tested: 7 sera from 4 patients with confirmed hydatidosis, 4 patients with discrepant serological results using the usual techniques of our laboratory (IFI and ES), one patient without any parasitic disease, and 6 patients with parasitic diseases other than hydatidosis (one with distomatosis, one with toxocarosis, two with alveolar echinococcosis and two with cysticercosis). All 4 patients with proven hydatidosis had a positive WB assay. The diagnosis of hydatidosis was confirmed in one patient with discordant results (IFI/ES) and eliminated for the 3 remaining patients, in which these data were clinically confirmed later on. The negative patient had a negative WB. Of the 6 patients with other parasitic diseases, one with cysticercosis and one with alveolar echinococcosis had a positive WB pattern. Both western-blot assays produced similar results for all patients, although they did not reveal the same proteins. These data provide evidence that WB is a valuable confirmation technique.