Skip to main content
NCBI home page
NIHPA Author Manuscripts logoLink to NIHPA Author Manuscripts
. Author manuscript; available in PMC: 2017 Nov 1.
Published in final edited form as: Brain Behav Immun. 2016 Apr 22;58:52–56. doi: 10.1016/j.bbi.2016.04.009

Cerebral complement C1q activation in chronic Toxoplasma infection

Jianchun Xiao a, Ye Li a, Kristin L Gressitt a, Helen He a, Geetha Kannan b,c, Tracey L Schultz c, Nadezhda Svezhova c, Vern B Carruthers c, Mikhail V Pletnikov b, Robert H Yolken a, Emily G Severance a,1
PMCID: PMC5067173  NIHMSID: NIHMS784001  PMID: 27109609

Abstract

Exposure to the neurotropic parasite, Toxoplasma gondii, causes significant brain and behavioral anomalies in humans and other mammals. Understanding the cellular mechanisms of T. gondii-generated brain pathologies would aid the advancement of novel strategies to reduce disease. Complement factor C1q is part of a classic immune pathway that functions peripherally to tag and remove infectious agents and cellular debris from circulation. In the developing and adult brain, C1q modifies neuronal architecture through synapse marking and pruning. T. gondii exposure and complement activation have both been implicated in the development of complex brain disorders such as schizophrenia. Thus, it seems logical that mechanistically, the physiological pathways associated with these two factors are connected. We employed a rodent model of chronic infection to investigate the extent to which cyst presence in the brain triggers activation of cerebral C1q. Compared to uninfected mice, cortical C1q was highly expressed at both the RNA and protein levels in infected animals bearing a high cyst burden. In these mice, C1q protein localized to cytoplasm, adjacent to GFAP-labeled astrocytes, near degenerating cysts, and in punctate patterns along processes. In summary, our results demonstrated an upregulation of cerebral C1q in response to latent T. gondii infection. Our data preliminarily suggest that this complement activity may aid in the clearance of this parasite from the CNS and in so doing, have consequences for the connectivity of neighboring cells and synapses.

Keywords: toxoplasmosis, psychiatry, prefrontal cortex, MAG1 antibodies, neurons, glia

1. Introduction

Exposure to the neurotropic parasite Toxoplasma gondii causes significant brain and behavioral alterations based on studies of experimental rodent models and human diseases (Flegr, 2007; Kannan and Pletnikov, 2012; Webster, 2001; Xiao et al., 2009). The mechanisms by which T. gondii may precipitate central nervous system (CNS) effects are not clear, although proposed hypotheses include parasite alterations of host dopamine pathways, direct silencing of infected neurons by parasite products, and parasite-mediated acetylation of proteins in cortical astrocytes (Bouchut et al., 2015; Haroon et al., 2012; Prandovszky et al., 2011). Investigations of pathways exploited by T. gondii are complicated by its complex developmental stages, progression of infection, diversity of strains and differential host susceptibilities. The T. gondii life cycle involves differentiation from a rapidly replicating tachyzoite mobile form to a relatively dormant bradyzoite form contained within cysts. The virulence of T. gondii strains varies significantly, ranging from the highly virulent (e.g. Type I) to intermediate or non-virulent phenotypes (e.g. Types II and III) (Halonen and Weiss, 2013).

Complement C1q is an immune protein that bridges innate and adaptive immunity and functions to clear antigen-antibody immune complexes from systemic circulation (Walport, 2001). A role for C1q in the pathogenesis of complex brain disorders is particularly intriguing as C1q helps to mediate synapse pruning during development and in adult neurodegenerative processes (Stephan et al., 2013; Stevens et al., 2007). The complement pathway has been primarily examined in T. gondii in the context of the initial immune response directed at the invading mobile tachyzoite. In these studies, complement components were critical response factors, but were also targets of parasite-mediated evasion (Fuhrman and Joiner, 1989a, b; Sacks and Sher, 2002; Schreiber and Feldman, 1980). When infection enters a chronic phase, tissue cysts are formed and predominantly located in the CNS for the lifetime of the host. Such persistence of tissue cysts requires a continuous immune response provided by resident CNS and/or infiltrating peripheral immune cells to prevent cyst reactivation and toxoplasmic encephalitis (Nance et al., 2012). It is possible that C1q is one such factor involved in this long-term, anti-parasite immune response.

Our goal was to evaluate the expression and localization of cerebral C1q in chronic T. gondii infection. Employing a virulent Type I strain infection model, we first investigated overall cortical C1q mRNA and protein abundances in mice bearing different levels of cysts. We then visualized C1q cellular expression and interactions with these cysts using immunohistochemistry. To accommodate the possibility that host C1q expression might vary according to parasite strain virulence, we expanded the immunolabelling portion to also include mice infected with a less virulent Type II strain. In this preliminary report, we demonstrate that irrespective of infection model, C1q activation occurs during chronic toxoplasmosis as part of the immune response directed against the bradyzoite cyst.

2. Material and methods

2.1 Chronic models of T. gondii infection

All mouse specimens were collected as part of ongoing projects; no additional animals were sacrificed for the present study. Animals were humanely sacrificed according to the Animal Protection Protocols at our respective institutions and consistent with the National Institutes of Health guide for the care and use of laboratory animals.

2.1.1 Chronic T. gondii Type I infection

Seven- to nine-week old female outbred CD-1 mice (ICR-Harlan Sprague) were infected intraperitoneally (i.p.) with 500 T. gondii GT1 strain tachyzoites (Type I, virulent). Control mice received vehicle only (PBS). To establish a chronic infection with this virulent strain, both control and infected mice were treated with anti-T. gondii chemotherapy (sulfadiazine sodium) in drinking water (400 mg/L, Sigma) from day 5-30. Mice were sacrificed at 5 months post infection. For qPCR and western blot experiments, prefrontal cortex was rapidly dissected and stored at -80 °C. For immunofluorescent staining, brains were immediately frozen at -80 °C and sectioned sagittally at 5-10 microns.

Upon sacrifice, blood samples were collected and serum isolated for immunoassays. T. gondii infection was confirmed using a commercial ELISA kit (VIR-ELISA, Viro-Immun Labor-Diagnostika, Oberursel Germany), and cyst burden determined using previously developed cyst matrix antigen 1 (MAG1) assays (Xiao et al., In press; Xiao et al., 2013). The median MAG1 antibody absorbance value (0.5) was the cutoff designation to stratify mice into high and low MAG1 groups (MAG1 high, MAG1 low) (Budczies et al., 2012). A second more stringent cutoff (1.0) was also assessed to accommodate bifurcated MAG1 distributions. Control animals had no MAG1 antibodies.

2.1.2 Chronic T. gondii Type II infection

We included a second mouse cohort infected with the less virulent Type II parasites to examine immunohistochemistry reproducibility and evaluate possible parasite and host strain variability. Seven-week old female CBA/J mice were infected i.p. with 18 mouse brain-derived ME49 strain cysts for 5 weeks, followed by daily i.p. injection of 50 μl DMSO (control for a separate treatment study) before sacrificing. Following dissection, brains were immediately placed in 4% paraformaldehyde, fixed for at least 24 hours and transferred to PBS for paraffin embedding and sectioning at 5-10 microns.

2.2 Quantitative PCR

RNA was isolated from mouse prefrontal cortex and quantitative PCR performed according to manufacturer's protocol using inventoried TaqMan mRNA assays (Life Technologies, Grand Island, NY, USA), as previously described (Xiao et al., 2011). Fold changes between groups were evaluated using relative quantification (delta Ct method); β-actin was the endogenous control.

2.3 Western blotting

Mouse prefrontal cortex was homogenized in RIPA buffer (Sigma, St Louis, MO, USA) containing protease inhibitors, sonicated 5 min at 4 °C, and centrifuged 5 min at 10,000g. Proteins were probed with a C1q-A primary antibody (1: 1000, Santa Cruz Biotechnology, Dallas, TX, USA). Bands were visualized using enhanced chemiluminescence (ECL Prime Western Blotting Detection Reagent, GE Healthcare Life Sciences, Piscataway, NJ, USA). Protein values were normalized for corresponding values of β-actin. Relative optical density was assessed using Scanalytics image analysis software (Bio-Rad, Hercule, CA, USA).

2.4 Immunofluorescence assays

For fixed frozen tissue sections, slides were washed with PBS followed by a 30 min block (0.025% Triton X, 10% donkey serum) at room temperature. For paraffin-embedded sections, slides were treated in xylene and a graduated alcohol series and rinsed in distilled water. Antigen retrieval occurred overnight at 60°C in 0.1 M sodium citrate (pH 6.0). For both section types, the primary antibody was incubated overnight at 4°C. Secondary antibodies were applied for 30 min to one hour. Slides were viewed at 400-1000× and images recorded using an Olympus BX41 microscope and reflected fluorescence system.

We used the following primary antibodies: 1:1000 goat polyclonal anti-C1qa antibody (Santa Cruz Biotechnology, Dallas, TX, USA); 1:70 rabbit monoclonal anti-C1q antibody (Abcam, Cambridge, MA, USA); 1:200 rat monoclonal anti-C1q antibody (Abcam); 1:1000 rabbit polyclonal anti-GFAP antibody (Abcam); 1:200 lectin direct 488 and 594 conjugates (Fluorescein Dolichos Biflorus Agglutinin, Vector Laboratories, Inc., Burlingame, CA, USA). Secondary antibodies were purchased from Life Technologies, Inc. (Frederick, MD, USA).

2.5 Statistical analyses

Analysis of variance (ANOVA) was performed to compare means between three MAG1-designated groups in qPCR and immunoblotting experiments. Bonferroni multiple comparison and Sidak post-hoc corrections were applied. Linear regression analysis of C1q and MAG1 antibodies was performed using two-tailed Spearman's correlation coefficient (r). P-values less than 0.01 were considered statistically significant. Statistical analyses were conducted in GraphPad Prism V5.02 (GraphPad Software Inc., La Jolla, CA, USA) and STATA version 12 (STATA Corp LP, College Station, Texas, U.S.A.).

3. Results

3.1 Cyst-associated elevation of cerebral C1q mRNA and protein

In Type I strain-infected CD-1 mice, we found significant cyst-associated elevations of cerebral C1q, irrespective of the MAG1 cut-off values used (0.5, 1.0) and here we report results using the 0.5 cutoff. C1q mRNA levels were increased approximately 4-fold in MAG1 high compared to MAG1 low or control groups (n=8 mice/group, F(2, 21)=9.71, p<0.001, post-hoc p<0.003-0.004, Fig. 1A). Cortical C1q mRNA levels were significantly correlated with MAG1 antibody levels (r=0.71, p=0.0019, Fig. 1B). Cortical C1q protein levels were significantly increased (approximately 9-fold) in MAG1 high mice compared to the other two groups (n=4 mice/group, F(2,9)=121.5, p<0.0001; post-hoc p<0.001, Fig. 1C). C1q protein levels positively correlated with serological levels of MAG1 (r=0.91, p=0.0046, Fig. 1D).

Figure 1.

Figure 1

Open in a new tab

Upregulation of brain C1q mRNA and protein in mice bearing a high burden of T. gondii Type I cysts. Transcriptional (A) and translational (C) C1q levels were elevated in brains of MAG1 high CD-1 mice compared to MAG1 low and to controls. Shown are means + standard deviations (A). Transcriptional (B) and translational (D) expression of C1q had strong positive correlations with continuous distributions of MAG1 cyst burden index.

3.2 C1q cellular localization and proximity to T. gondii cysts

In Type I-infected CD-1 mice, cerebral C1q expression occurred primarily with those who had high MAG1 levels (Fig. 2A) compared to uninfected controls (Fig. 2B). Cellular C1q immunolabelling was predominantly cytoplasmic and occurred in association with cells stained with GFAP (Fig. 2C-D). For example, C1q expression encompassed the entire cytoplasmic region of one cell whereas its neighboring cell exclusively expressed GFAP in its cytoplasm and processes (Panel 2C).

Figure 2.

Figure 2

Open in a new tab

Brain C1q localization in T. gondii Type I- and Type II-infected mice. C1q immune-positive staining occurred in MAG1 high, Type I-infected CD-1 mice (A) but not in uninfected controls (B). In these CD-1 mice, C1q expression was predominantly cytoplasmic (green arrows) and in the vicinity of GFAP-expressing astrocytes (red arrow) (C-D). In both infection models (Type II shown here), breached cyst walls (green arrow) and cyst decomposition (red arrow) were C1q-associated (E). Punctate C1q staining was observed in and around Type II cysts (F). A-B: rabbit anti-C1q monoclonal, white bar=20 microns, CD-1 mice, Type I strain infection. CD: rat anti-C1q monoclonal, white bar=12.5 microns, CD-1 mice, Type I infection. E-F: goat anti-C1q polyclonal, white bar=20 microns, CBA/J mice, Type II infection.

Because results from the mRNA, protein and immunohistochemistry examinations all suggest particularly strong C1q expression in the brains of mice with a high cyst burden, we examined C1q-cyst co-localizations by labeling cyst walls with Dolichos biflorus lectin. In both Type I and Type II infection models, C1q expression was observed in conjunction with different degrees of breached cyst barriers (Panel 2E). C1q immunolabelling also occurred in punctate patterns indicative of synapses along neuronal cell processes (Panel 2F). Additional representative examples of C1q co-localizations and negative control images can be found in Supplemental Figure 1.

4. Discussion

Here, we confirm that chronic T. gondii infection results in an elevated expression of cerebral cortical C1q at both the mRNA and protein level. Such increases were triggered in association with measures of parasite cyst burden. C1q upregulation occurred subcellularly in cytoplasm, in proximity to GFAP-expressing astrocytes and in punctate patterns indicative of synapse involvement. C1q also directly localized in the vicinity of parasite cysts and particularly with those in different stages of rupture or degeneration. Given the role that C1q has in developmental and adult synaptic plasticity, and the integral linkage of these processes with behavior, we can hypothesize that T. gondii exerts its long-term behavioral anomalies at least in part through C1q activation and interaction with bradyzoite cysts.

Previous microarray and high throughput sequencing analyses reported the upregulation of brain C1q mRNA during chronic T. gondii infection (Hermes et al., 2008; Tanaka et al., 2013). Our study extends these findings by documenting dramatic increases not only of C1q mRNA but also C1q protein selectively in those murine brains that had significant evidence of high cyst burden. These findings are consistent with the antigen-associated principle for C1 complex activation and further suggest that cysts located in the brain initiate the brain's immune system through a complement pathway mechanism. It is conceivable that mice designated as MAG1 low have insufficient levels of the antigenic triggers needed to stimulate the complement machinery.

The association of cortical elevations of C1q mRNA and protein with T. gondii cyst burden was further substantiated by the precise C1q localization in the vicinity of cysts in the immunofluorescence images. Similar patterns in both parasite strain and host strain models suggest that C1q activation is part of a generalized anti-T. gondii immune response during chronic infection, which occurs regardless of infecting strain type. Interestingly, C1q seemed to interact primarily with degenerate cysts, an indication that a compromised cyst wall likely results in the exposure of additional T. gondii moieties that C1q might recognize as targets for selective elimination. Punctate staining in surrounding regions were indicative of synapse tagging, suggesting that cyst removal via this C1q mechanism may include cytological consequences for associated neurons. Increased C1q expression caused by chronic T. gondii infection raises the possibility that neurodegeneration, as characterized by possible synapse loss or neuronal death through tagging, is occurring. The mechanisms involved in cyst rupture are not known, yet in our study, C1q and GFAP-labeled astrocytes appear to be active components of this process.

In conclusion, our results implicate C1q in the neuropathogenesis of chronic toxoplasmosis and specifically support the bradyzoite cyst stage as a trigger for complement activation. Previous reports show that C1q is upregulated in a range of complex brain disorders and conditions including aging, Alzheimer's disease, multiple sclerosis and schizophrenia (Francis et al., 2003; Michailidou et al., 2015; Severance et al., 2014; Severance et al., 2012; Stephan et al., 2013). Excessive synapse pruning in schizophrenia may be mediated in part by polymorphisms of the complement C4 gene (Sekar et al., 2016), the product of which binds C1q in the classic complement pathway. In the context of our own study findings, the significant association of T. gondii exposures in human psychiatric disorders (Markovitz et al., 2015; Torrey et al., 2012) suggests a mechanism of pathogenicity that involves interacting early complement components. Therapeutic strategies aimed to treat the chronic T. gondii stage might consider supplemental immune-modulatory agents in addition to therapies that directly target the organism.

Supplementary Material

Supplemental Figure 1

Additional images of brain C1q localization experiments in T. gondii-infected mice. A: cytoplasmic C1q. B: breached cyst wall (red arrow) encompassed by C1q (green arrow). C: deteriorating cyst. D: punctate C1q surrounding cyst. E-F: No primary antibody negative controls. A-B: rat anti-C1q monoclonal, white bar=12.5 microns, CD-1, Type I. C-D: goat anti-C1q polyclonal, white bar=10 microns, CBA/J, Type II.

Highlights.

  • Complement activation and exposure to Toxoplasma are risk factors for schizophrenia.

  • Here, Toxoplasma infection in mice caused elevated brain C1q mRNA and protein.

  • C1q expression localized close to parasite cysts and in punctate synaptic patterns.

  • Parasite clearance from the brain by complement may impact cellular connectivities.

Acknowledgments

This work was supported by a NIMH P50 Silvio O. Conte Center at Johns Hopkins (grant# MH-94268) and by the Stanley Medical Research Institute.

Footnotes

Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

References

  1. Bouchut A, Chawla AR, Jeffers V, Hudmon A, Sullivan WJ., Jr Proteome-wide lysine acetylation in cortical astrocytes and alterations that occur during infection with brain parasite Toxoplasma gondii. PloS One. 2015;10(3):e0117966. doi: 10.1371/journal.pone.0117966. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Budczies J, Klauschen F, Sinn BV, Gyorffy B, Schmitt WD, Darb-Esfahani S, Denkert C. Cutoff Finder: a comprehensive and straightforward Web application enabling rapid biomarker cutoff optimization. PLoS One. 2012;7(12):e51862. doi: 10.1371/journal.pone.0051862. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Flegr J. Effects of Toxoplasma on human behavior. Schizophr Bull. 2007;33(3):757–760. doi: 10.1093/schbul/sbl074. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Francis K, van Beek J, Canova C, Neal JW, Gasque P. Innate immunity and brain inflammation: the key role of complement. Expert Rev Mol Med. 2003;5(15):1–19. doi: 10.1017/S1462399403006252. [DOI] [PubMed] [Google Scholar]
  5. Fuhrman SA, Joiner KA. Complement evasion by protozoa. Exp Parasitol. 1989a;68(4):474–481. doi: 10.1016/0014-4894(89)90133-1. [DOI] [PubMed] [Google Scholar]
  6. Fuhrman SA, Joiner KA. Toxoplasma gondii: mechanism of resistance to complement-mediated killing. Journal of Immunology. 1989b;142(3):940–947. [PubMed] [Google Scholar]
  7. Halonen SK, Weiss LM. Toxoplasmosis. Handb Clin Neurol. 2013;114:125–145. doi: 10.1016/B978-0-444-53490-3.00008-X. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Haroon F, Handel U, Angenstein F, Goldschmidt J, Kreutzmann P, Lison H, Fischer KD, Scheich H, Wetzel W, Schluter D, Budinger E. Toxoplasma gondii actively inhibits neuronal function in chronically infected mice. PloS One. 2012;7(4):e35516. doi: 10.1371/journal.pone.0035516. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Hermes G, Ajioka JW, Kelly KA, Mui E, Roberts F, Kasza K, Mayr T, Kirisits MJ, Wollmann R, Ferguson DJ, Roberts CW, Hwang JH, Trendler T, Kennan RP, Suzuki Y, Reardon C, Hickey WF, Chen L, McLeod R. Neurological and behavioral abnormalities, ventricular dilatation, altered cellular functions, inflammation, and neuronal injury in brains of mice due to common, persistent, parasitic infection. J Neuroinflammation. 2008;5:48. doi: 10.1186/1742-2094-5-48. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Kannan G, Pletnikov MV. Toxoplasma gondii and cognitive deficits in schizophrenia: an animal model perspective. Schizophr Bulletin. 2012;38:1155–61. doi: 10.1093/schbul/sbs079. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Markovitz AA, Simanek AM, Yolken RH, Galea S, Koenen KC, Chen S, Aiello AE. Toxoplasma gondii and anxiety disorders in a community-based sample. Brain, Behavior, and Immunity. 2015;43:192–197. doi: 10.1016/j.bbi.2014.08.001. [DOI] [PubMed] [Google Scholar]
  12. Michailidou I, Willems JG, Kooi EJ, van Eden C, Gold SM, Geurts JJ, Baas F, Huitinga I, Ramaglia V. Complement C1q-C3-associated synaptic changes in multiple sclerosis hippocampus. Ann Neurol. 2015;77(6):1007–1026. doi: 10.1002/ana.24398. [DOI] [PubMed] [Google Scholar]
  13. Nance JP, Vannella KM, Worth D, David C, Carter D, Noor S, Hubeau C, Fitz L, Lane TE, Wynn TA, Wilson EH. Chitinase dependent control of protozoan cyst burden in the brain. PLoS Pathog. 2012;8(11):e1002990. doi: 10.1371/journal.ppat.1002990. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Prandovszky E, Gaskell E, Martin H, Dubey JP, Webster JP, McConkey GA. The neurotropic parasite Toxoplasma gondii increases dopamine metabolism. PloS One. 2011;6(9):e23866. doi: 10.1371/journal.pone.0023866. [DOI] [PMC free article] [PubMed] [Google Scholar]
  15. Sacks D, Sher A. Evasion of innate immunity by parasitic protozoa. Nat Immunol. 2002;3(11):1041–1047. doi: 10.1038/ni1102-1041. [DOI] [PubMed] [Google Scholar]
  16. Schreiber RD, Feldman HA. Identification of the activator system for antibody to Toxoplasma as the classical complement pathway. The Journal of Infectious Diseases. 1980;141(3):366–369. doi: 10.1093/infdis/141.3.366. [DOI] [PubMed] [Google Scholar]
  17. Sekar A, Bialas AR, de Rivera H, Davis A, Hammond TR, Kamitaki N, Tooley K, Presumey J, Baum M, Van Doren V, Genovese G, Rose SA, Handsaker RE, Daly MJ, Carroll MC, Stevens B, McCarroll SA. Schizophrenia risk from complex variation of complement component 4. Nature. 2016;530:177–83. doi: 10.1038/nature16549. [DOI] [PMC free article] [PubMed] [Google Scholar]
  18. Severance EG, Gressitt KL, Buka SL, Cannon TD, Yolken RH. Maternal complement C1q and increased odds for psychosis in adult offspring. Schizophrenia Research. 2014;159(1):14–19. doi: 10.1016/j.schres.2014.07.053. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Severance EG, Gressitt KL, Halling M, Stallings CR, Origoni AE, Vaughan C, Khushalani S, Alaedini A, Dupont D, Dickerson FB, Yolken RH. Complement C1q formation of immune complexes with milk caseins and wheat glutens in schizophrenia. Neurobiol Dis. 2012;48(3):447–453. doi: 10.1016/j.nbd.2012.07.005. [DOI] [PMC free article] [PubMed] [Google Scholar]
  20. Stephan AH, Madison DV, Mateos JM, Fraser DA, Lovelett EA, Coutellier L, Kim L, Tsai HH, Huang EJ, Rowitch DH, Berns DS, Tenner AJ, Shamloo M, Barres BA. A dramatic increase of C1q protein in the CNS during normal aging. J Neurosci. 2013;33(33):13460–13474. doi: 10.1523/JNEUROSCI.1333-13.2013. [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Stevens B, Allen NJ, Vazquez LE, Howell GR, Christopherson KS, Nouri N, Micheva KD, Mehalow AK, Huberman AD, Stafford B, Sher A, Litke AM, Lambris JD, Smith SJ, John SW, Barres BA. The classical complement cascade mediates CNS synapse elimination. Cell. 2007;131(6):1164–1178. doi: 10.1016/j.cell.2007.10.036. [DOI] [PubMed] [Google Scholar]
  22. Tanaka S, Nishimura M, Ihara F, Yamagishi J, Suzuki Y, Nishikawa Y. Transcriptome analysis of mouse brain infected with Toxoplasma gondii. Infection and Immunity. 2013;81(10):3609–3619. doi: 10.1128/IAI.00439-13. [DOI] [PMC free article] [PubMed] [Google Scholar]
  23. Torrey EF, Bartko JJ, Yolken RH. Toxoplasma gondii and other risk factors for schizophrenia: an update. Schizophrenia Bulletin. 2012;38(3):642–647. doi: 10.1093/schbul/sbs043. [DOI] [PMC free article] [PubMed] [Google Scholar]
  24. Walport MJ. Complement. First of two parts. The New England Journal of Medicine. 2001;344(14):1058–1066. doi: 10.1056/NEJM200104053441406. [DOI] [PubMed] [Google Scholar]
  25. Webster JP. Rats, cats, people and parasites: the impact of latent toxoplasmosis on behaviour. Microbes Infect. 2001;3(12):1037–1045. doi: 10.1016/s1286-4579(01)01459-9. [DOI] [PubMed] [Google Scholar]
  26. Xiao J, Buka SL, Cannon TD, Suzuki Y, Viscidi RP, Torrey EF, Yolken RH. Serological pattern consistent with infection with type I Toxoplasma gondii in mothers and risk of psychosis among adult offspring. Microbes Infect. 2009;11(13):1011–1018. doi: 10.1016/j.micinf.2009.07.007. [DOI] [PubMed] [Google Scholar]
  27. Xiao J, Jones-Brando L, Talbot CC, Jr, Yolken RH. Differential effects of three canonical Toxoplasma strains on gene expression in human neuroepithelial cells. Infection and Immunity. 2011;79(3):1363–1373. doi: 10.1128/IAI.00947-10. [DOI] [PMC free article] [PubMed] [Google Scholar]
  28. Xiao J, Li Y, Prandovszky E, Kannan G, Viscidi RP, Pletnikov M, Yolken R. Behavioral abnormalities in a mouse model of chronic Toxoplasmosis are associated with MAG1 antibody levels and cyst burden. PLoS Negl Trop Dis. doi: 10.1371/journal.pntd.0004674. In press. [DOI] [PMC free article] [PubMed] [Google Scholar]
  29. Xiao J, Viscidi RP, Kannan G, Pletnikov MV, Li Y, Severance EG, Yolken RH, Delhaes L. The Toxoplasma MAG1 peptides induce sex-based humoral immune response in mice and distinguish active from chronic human infection. Microbes Infect. 2013;15(1):74–83. doi: 10.1016/j.micinf.2012.10.016. [DOI] [PMC free article] [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Supplemental Figure 1

Additional images of brain C1q localization experiments in T. gondii-infected mice. A: cytoplasmic C1q. B: breached cyst wall (red arrow) encompassed by C1q (green arrow). C: deteriorating cyst. D: punctate C1q surrounding cyst. E-F: No primary antibody negative controls. A-B: rat anti-C1q monoclonal, white bar=12.5 microns, CD-1, Type I. C-D: goat anti-C1q polyclonal, white bar=10 microns, CBA/J, Type II.

NIHMS784001-supplement.tiff (2.6MB, tiff)

RESOURCES