First case report of M1 macrophage polarization in an untreated symptomatic patient with toxoplasmosis
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In immunocompetent patients, acute toxoplasmosis is usually asymptomatic. We identified M1 macrophages in a case of symptomatic acute Toxoplasma gondii infection that resolved without treatment. M1 macrophages have been demonstrated in animal models of toxoplasmosis, but not in humans.
A 63-year-old woman presented with laterocervical and axillary bilateral lymphadenopathy. Her anamnesis defined an episode of high fever and prolonged asthenia 4 months previously, which suggested an infectious disease. Following laboratory, radiological, and pathological analyses, she was diagnosed with toxoplasmosis. Immunohistochemical analyses were performed on lymph node sections. More than 50% of the macrophages in the lymph node microgranulomas were M1 macrophages, defined by CD68+/p-Stat1+ staining, and the presence of T helper 1 lymphocytes indicated an immune response known to induce M1 macrophage polarization. Activated endothelial cells were found only in inflamed areas. No therapy was administered before or after diagnosis, and the lymphadenopathy resolved after a follow-up of 5 months.
This is the first report to demonstrate the presence of M1 macrophages in human toxoplasmosis. Our findings contribute to the understanding of the pathogenesis of toxoplasmosis, and encourage further studies on the role of macrophage polarization in human toxoplasmosis.
KeywordsToxoplasma gondii Macrophage polarization T helper 1 immune response Immunodeficiency
Inducible nitric oxide synthase
Phospho-signal transducer and activator of transcription 1
Signal transducer and activator of transcription 1
- T. gondii
Toxoplasmosis is a parasitic infection that can be life threatening in immunodeficient patients and when it is transmitted congenitally. In immunocompetent patients, the acute infection is mostly asymptomatic, and is clinically evident in only 10% of cases, presenting as a flu-like illness associated with lymphadenopathy. It is frequently benign and patients usually recover, although, chorioretinitis, hepatitis, myocarditis, or encephalitis can sometimes develop. In other cases, the acute infection can result in chronic persistence of cysts within the tissues of the hosts, for which an effective immune response is important [1, 2].
Macrophage polarization has different effects that influence the progression of inflammatory responses. M1 macrophages are activated by Toll receptor ligands and cytokines produced by T helper 1 lymphocytes, and they sustain inflammation . M2 macrophages are activated by various cytokines, including IL-4 produced by T helper II lymphocytes, and they show a wide spectrum of functions, including angiogenesis, immune suppression, and tissue remodeling and repair [1, 3]. In vitro studies have suggested that a subset of M2 macrophages predominates during inflammation repair, and that a switch from one functional phenotype to another is possible in response to microenvironmental signals [1, 3].
Most studies that have focused on macrophage polarization have been performed in vitro or in animal models [1, 3], and thus the characterization of macrophages in human diseases is an important issue. M1 macrophages have been demonstrated in experimental models of Toxoplasma gondii (T. gondii) infection, although not in humans. Interferon gamma (IFN-γ) produced by T lymphocytes is the major mediator of resistance against T. gondii . Activation of the transcription factor signal transducer and activator of transcription 1 (Stat1) is essential to mediate the antimicrobial effects of IFN-γ, particularly in the immune response against T. gondii . Stat1-deficient mice are indeed highly susceptible to this disease . In macrophages, IFN-γ induces Stat1 phosphorylation, dimerization and translocation to the nucleus, where it leads to the transcription of genes encoding proteins that are essential for the response to intracellular parasites (inducible nitric oxide synthase, also called iNOS, immunity-related GTPase and others) . Combined immunoreactivity for nuclear phospho-Stat1 (p-Stat1) and the membrane macrophage CD68 marker has been shown to identify M1 macrophages in human tissues . The CD68 antigen, which is specifically recognized by the PG-M1 monoclonal antibody, is considered the most specific marker available for all human macrophages [6, 7], thus a double CD68/p-Stat1 positivity clearly allows an accurate detection of the M1 macrophage subset. Using this method we identified M1 macrophages in a human T. gondii infection. Moreover, we observed CD31-positive endothelial cells with nuclear p-Stat1 immunoreactivity in areas with mononuclear cell infiltration, which suggests inflammation-induced endothelial cell activation.
Discussion and conclusions
We found that in a human T. gondii infection more than 50% of the macrophages in microgranulomas were polarized as M1 macrophages during the IgM seroreversion/IgG seroconversion, which corresponds to the late phase of the inflammatory response. In this phase, a small percentage of T-lymphocytes were p-Stat1 immunoreactive. In addition, IFN-γ and iNOS immunoreactive cells showed a similar localization. Our observations suggest that in the acute phase of the anti-T. gondii immune response T helper 1 lymphocytes produced IFN-γ stimulating the activation of the p-Stat1 driven antimicrobial pathways in macrophages.
In mice, T. gondii replication in brain endothelial cells precedes invasion of the central nervous system . Importantly, in vitro data have shown that cytokine-activated murine endothelium contributes to the clearance of T. gondii through recruitment of CD8+ lymphocytes . We observed human endothelial cells that expressed p-Stat1 in inflamed areas, where pStat-1+ mononuclear cells were present. It is tempting to speculate that human activated endothelial cells contribute to the anti-T. gondii immune response. In the present patient the infection self-resolved, which suggested that the M1 response led to healing and might have a major role in promoting an effective response. Recent results in animal models indicate that M2 macrophage polarization in T. gondii infection may be deleterious and be associated with chronic persistence .
Although our findings concern a single patient and cannot be generalized, they encourage studies about the role of macrophage polarization in toxoplasma chronic persistence and reactivation in human subjects.
Primary T. gondii infection in pregnancy is treated with spiramycin alone or in combination with other drugs, and the pooled rate of vertical transmission in treated patients after therapy is about 10% . Anti-parasitic treatment suppresses the production of specific IgM and IgG in mice  and decreases the production of IgG in pregnant women . Whether anti-parasitic therapy affects macrophage polarization remains to be investigated. To date, all studies concerning macrophage polarization in toxoplasmosis have been performed in experimental animal models. We identified for the first time a large number of M1 macrophages in a symptomatic case of human toxoplasmosis that spontaneously resolved.
We thank Drs. Fiorella Calabrese and Manuela Iezzi for providing anti-iNOS and IFN-γ antibodies, respectively, and Dr. Antonio Sisto for critical review of the manuscript.
Supported by funds from Ministero dell’Istruzione, dell’Università e della Ricerca, Italy. The funders had no role in the study design, data collection and analysis, decision to publish or preparation of the manuscript.
Availability of data and materials
The datasets used/and or analysed in this study are available from the corresponding authors on reasonable request.
All authors contributed to design the study. Acquisition, analysis and interpretation of data: GDL, CDL, GL. Immunohistochemical analyses: TD’A, ML. GDL and FBA wrote the manuscript. All authors have read and approved the manuscript.
Ethics approval and consent to participate
The study has been approved by the authors’ institutional review board (Comitato Etico delle Province di Chieti e Pescara).
Consent for publication
Written informed consent from the patient was obtained.
The authors have no competing interests to declare.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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