The antibody response in experimental ocular toxoplasmosis

Wild Rabbit Exposure to Leishmania infantum, Toxoplasma gondii, Anaplasma phagocytophilum and Babesia caballi Evidenced by Serum and Aqueous Humor Antibody Detection

Wild rabbits (Oryctolagus cuniculus) can be important sentinel species for the presence of zoonotic pathogens. Therefore, we collected blood samples from wild rabbits harvested by hunters during the hunting season 2019–2020 on the island of Lemnos, to determine exposure of wild rabbits to the zoonotic pathogens Leishmania infantum, Toxoplasma gondii, Anaplasma phagocytophilum and Babesia caballi, as well as aqueous humor to assess its diagnostic performance in terms of sensitivity, specificity, positive and negative likelihood ratios. Antibodies against these pathogens were detected by Indirect Immunofluorescence Antibody (IFA) assay. Out of the 72 wild rabbits included in the study, 4.2%, 5.5%, 18% and 9.7% were seropositive to L. infantum, T. gondii, A. phagocytophilum and B. caballi, respectively. Although less frequently, antibodies were also detected in aqueous humor of wild rabbits. The antibody detection in aqueous humor presented 100% specificity but decreased sensitivity compared to serum suggesting that aqueous humor could be successfully used in epidemiological studies to confirm exposure at the population level but has little diagnostic value at the individual level. This is the first report on the seropositivity of wild rabbits to A. phagocytophilum and B. caballi and the detection of antibodies against A. phagocytopylum, L. infantum, T. gondii and B. caballi in the aqueous humor.

Risks and Challenges in Interpreting Simultaneous Analyses of Multiple Cytokines

Purpose

To determine the inherent risks of handling results below the lowest detectable value in the analysis of multiple cytokines in the aqueous humor of patients with retinal diseases by comparing possible statistical strategies to lower the risk of mis interpretation or over interpretation of results. Furthermore, in analyzing multiple cytokines simultaneously, the challenge of multiple comparison arises.

Methods

The analyses were based on parallel testing of 43 cytokines in 58 aqueous humor samples from patients with macular hole or epiretinal membrane. Substitution of values below the detection limit with 0.1 ×, 0.5 ×, or 1.0× of the lowest level of quantitation was compared with handling as missing value. The impact of correction for multiple comparisons was assessed using the Holm correction.

Results

When comparing macular hole with epiretinal membrane, not substituting the missing data revealed a difference (P < 0.05) for five compared with wight cytokines after their substitution, indicating an increased risk for under-estimating group differences (type II error). Correcting for multiple comparisons revealed a relevant risk of over estimating group differences (type I error).

Conclusions

Physiologic cytokine concentrations in ocular fluids typically range at or below the lowest level of quantitation. Handling of results below this cutoff as missing leads to increased type II errors. Not correcting for multiple comparisons increases the risk of a type I error. Taken together, both harbor a systematic inherent risk of misinterpretation of the results.

Translational Relevance

Ignoring the inherent risks of data misinterpretation in analyses of ocular fluid samples may result in mis leading conclusions regarding their biological relevance.

Biological Diagnosis of Ocular Toxoplasmosis: a Nine-Year Retrospective Observational Study

Ocular toxoplasmosis (OT), a parasitic infection of the eye, is considered to be the most important infectious cause of posterior uveitis worldwide. Its prevalence is particularly high in South America, where aggressive Toxoplasma gondii strains are responsible for more-severe presentations. The particular pathophysiology of this infection leads, from recurrence to recurrence, to potentially severe vision impairment. The diagnosis of this infection is usually exclusively based on the clinical examination. However, the symptoms may be misleading and are not always sufficient to confirm a diagnosis of OT. In such cases, biological tests performed by means of several techniques on blood and ocular samples may facilitate the diagnosis. In this study, we analyzed the tests that were performed in our laboratory over a 9-year period every time OT was suspected. Our report highlights that the quality of ocular sampling by ophthalmologists and combinations of several techniques are critical for a reliable biological OT diagnosis.

Ocular toxoplasmosis (OT), i.e., the ocular manifestation of Toxoplasma gondii infection, is one of the leading causes of posterior uveitis. While ocular lesions are often typical, atypical forms often require biological confirmation of the diagnosis. Our study sought to review the biological OT diagnoses made in our laboratory to further assess the role of each test in the diagnostic procedure. All ocular samples sent to our laboratory over the last 9 years for OT diagnosis were included. These samples were analyzed using T. gondii PCR and antibody detection by means of immunoblotting and Candolfi coefficient (CC) determinations, either alone or in combination. Since serum analysis is required to interpret both the CC and immunoblotting, blood serology for T. gondii was also performed in most cases. Of the 249 samples analyzed, 80 (32.1%; 95% confidence interval [95%CI], 26.3 to 37.9) were positive for OT. Of these 80 cases, 52/80 (65.0%; 54.6 to 74.5) displayed a positive PCR, 15/80 (18.8%; 10.2 to 27.3) a positive CC, and 33/80 (41.3%; 95%CI, 30.5 to 52.0) a positive immunoblot result. Overall, 63 of the 80 OT diagnoses (78.8%; 95%CI, 69.8 to 87.7) were made on the basis of a single positive test result. Our study results remind us that current biological diagnostic tools for OT must be employed in combination to obtain an optimal diagnosis based on the precious ocular fluids sampled by ophthalmologists. Clinicobiological studies that are focused on correlating the performances of the different tests with clinical features are critically needed to improve our understanding of the pathophysiology and diagnosis of OT.

IMPORTANCE Ocular toxoplasmosis (OT), a parasitic infection of the eye, is considered to be the most important infectious cause of posterior uveitis worldwide. Its prevalence is particularly high in South America, where aggressive Toxoplasma gondii strains are responsible for more-severe presentations. The particular pathophysiology of this infection leads, from recurrence to recurrence, to potentially severe vision impairment. The diagnosis of this infection is usually exclusively based on the clinical examination. However, the symptoms may be misleading and are not always sufficient to confirm a diagnosis of OT. In such cases, biological tests performed by means of several techniques on blood and ocular samples may facilitate the diagnosis. In this study, we analyzed the tests that were performed in our laboratory over a 9-year period every time OT was suspected. Our report highlights that the quality of ocular sampling by ophthalmologists and combinations of several techniques are critical for a reliable biological OT diagnosis.

When biology supports clinical diagnosis: review of techniques to diagnose ocular toxoplasmosis

Toxoplasmosis is a common infection whose worldwide prevalence is estimated at 30%, with large disparities across the world. Among infected subjects, the prevalence of ocular toxoplasmosis (OT) is, however, limited to about 2% in Europe and 17% in South America. In France, it is estimated that about 1 000 000 patients present either active OT or subsequent chorioretinal scars. Toxoplasmagondii is the first cause of posterior uveitis worldwide, responsible for retinochoroiditis, at times associated with anterior uveitis. To date, there is no consensus yet on how to diagnose OT, which is often based only on clinical presentation. Nevertheless, OT-associated symptoms are often atypical and misleading. Over the last 20 years, tremendous progress has been made in biological tools, enabling parasitologists to confirm the diagnosis in most suspected cases of OT. Using anterior chamber puncture, a safe and fast procedure, ophthalmologists sample aqueous humour for analysis using multiple techniques in order to reach high specificity and sensitivity in OT diagnosis. In this article, we present the different techniques available for the biological diagnosis of OT, along with their characteristics, and propose a diagnostic algorithm designed to select the best of these techniques if clinical examination is not sufficient to ascertain the diagnosis.

Comparison of immunoblotting (IgA and IgG) and the Goldmann-Witmer coefficient for diagnosis of ocular toxoplasmosis in immunocompetent patients

BACKGROUND

Ocular toxoplasmosis (OT) is a common cause of posterior uveitis worldwide. The diagnosis of OT is based on clinical findings, but in most cases, laboratory tests are required to confirm the aetiology, especially when other diseases are suspected. The aim of this study was to evaluate which methods, between the Goldmann-Witmer coefficient (GWC) and immunoblotting (IB) with both IgG and IgA, in aqueous humour (AH) samples, can be the most sensitive to diagnose OT, in current practice, especially in the first three weeks.

METHODS

Retrospectively reviewed records of 87 consecutive patients who had underwent AH and serum sample, 42 patients with suspected OT and 45 patients with suspected other ocular inflammatory diseases. All samples were analysed by both GWC and IB.

RESULTS

The GWC was significant in 47.6% of patients presenting with suspected OT. The intraocular production of specific antibody anti-Toxoplasma gondii IgG and IgA was revealed by IB in 71.4% of samples. The combination of these two methods increased the sensitivity to 76.2%. Based on the interval between symptom onset and paracentesis, IB had a greater sensitivity than GWC when sample of AH was taken in the first three weeks (64.7% vs 23.5%, P=0.039), while the difference between the sensitivity of IB and GWC was less important in cases with an interval >3 weeks (76% vs 64% P=0.625).

CONCLUSION

IB seems to be more useful than the GWC if only one of these methods can be performed, especially during the first three weeks after symptom onset.

Diagnostic approach to ocular toxoplasmosis

Toxoplasmic retinochoroiditis is deemed a local event, which may fail to evoke a detectable systemic immune response. A correct diagnosis of the disease is a necessary basis for estimating its clinical burden. This is not so difficult in a typical clinical picture. In atypical cases, further diagnostic efforts are to be installed. Although the aqueous humor may be analyzed for specific antibodies or the presence of parasitic DNA, the DNA burden therein is low, and in rare instances a confirmation would necessitate vitreous sampling. A laboratory confirmation of the diagnosis is frustrated by individual differences in the time elapsing between clinical symptoms and activation of specific antibody production, which may result in false negatives. In congenital ocular toxoplasmosis, a delay in the onset of specific local antibody production could reflect immune tolerance. Herein, the authors attempt to provide a simple and practicable algorithm for a clinically tailored diagnostic approach in atypical instances.

Anti-retinal autoantibodies in experimental ocular and systemic toxoplasmosis

BACKGROUND

Patients with ocular toxoplasmosis (OT) develop autoreactivity to several retinal antigens, including retinal S-antigen. By establishing an experimental rabbit model of systemic and of primary and secondary ocular toxoplasmosis, we wished to investigate the onset and development of humoral response to retinal S-antigen.

METHODS

Of twelve infection-naïve rabbits, six were left untreated, and the other six were infected subcutaneously with 5,000 tachyzoites of the highly virulent, non-cyst-forming BK-strain of Toxoplasma gondii. Three months later, the left eye of each animal was infected transvitreally with 5,000 tachyzoites of the same strain. The right eye of each rabbit served as an uninfected control. Blood and aqueous humor were collected prior to infection, and up to 90 days thereafter. Using the ELISA technique, all samples were analyzed in parallel for total IgG, and antibodies against toxoplasmic, bovine retinal S-antigen and peptide 35 from human S-antigen.

RESULTS

In infection-naïve rabbits Toxoplasma-specific antibodies were detected 10 to 15 days after systemic and ocular infection. Serum antibodies against retinal S-antigen and peptide 35 were not detected in response to systemic Toxoplasma infection. After ocular challenge, aqueous-humour levels of antibodies against retinal S-antigen and peptide 35 in the infected eye began to rise 10 to 15 days later in infection-naïve, but not in infection-immunized animals. During the early post-infection period, the concentrations of anti-retinal antibodies in the infected eye correlated with the severity of inflammatory tissue destruction, but returned to baseline later even though the inflammatory response persisted. In the uninfected partner eye, concentrations of anti-retinal and toxoplasmic antibodies did not correlate with each other.

CONCLUSION

Our data afford no evidence of similarities between toxoplasmic and retinal antigens, nor of infection-induced humoral autoimmunity. They indicate rather that retinal autoantigens are liberated in the context of inflammatory tissue destruction due to ocular toxoplasmosis.

The temperature-sensitive mutants of Toxoplasma gondii and ocular toxoplasmosis

The risk of blindness caused by ocular toxoplasmosis supports efforts to improve our understanding for control of this disease. In this study, the involvement of CD8(+), CD4(+), B cell, and IL-10 gene in the immune response of primary ocular infection with the temperature-sensitive mutant (ts-4) of the RH Toxoplasma gondii strain, and in the protective immunity of ocular ts-4 vaccination and challenge with RH strain was investigated in murine models utilizing inbred C57BL/6 mice-deficient in CD4(+), CD8(+), B cells (microMT), or IL-10 gene. Compared to naive mice, all WT and mutant mice had different degree of ocular pathological changes after ts-4 ocular infection, in which both CD8 KO and IL-10 KO mice showed the most severe ocular lesions. Immunized by ts-4 intracameral (i.c.) inoculation, all mutant mice had partially decreased vaccine-induced resistance associated with increased ocular parasite burdens after RH strain challenge. A significant increase of the percentages of B cells and CD8(+) T cells in the draining lymph nodes were observed in WT and IL-10 KO mice after either infection or challenge. The levels of specific anti-toxoplasma IgG in both eye fluid and serum from all the mice were significantly increased after ts-4 i.c. immunization, except microMT mice. These results suggest that the avirulent ts-4 of T. gondii inoculated intracamerally can induce both ocular pathology and ocular protective immunity; CD4(+), CD8(+), B cell, and IL-10 gene are all necessary to the vaccine-induced resistance to ocular challenge by virulent RH strain, in which CD8(+) T cells are the most important component.