Immune response and pathogen invasion at the choroid plexus in the onset of cerebral toxoplasmosis

Abstract

Background Toxoplasma gondii (T. gondii) is a highly successful parasite being able to cross all biological barriers of the body, finally reaching the central nervous system (CNS). Previous studies have highlighted the critical involvement of the blood–brain barrier (BBB) during T. gondii invasion and development of subsequent neuroinflammation. Still, the potential contribution of the choroid plexus (CP), the main structure forming the blood–cerebrospinal fluid (CSF) barrier (BCSFB) have not been addressed. Methods To investigate T. gondii invasion at the onset of neuroinflammation, the CP and brain microvessels (BMV) were isolated and analyzed for parasite burden. Additionally, immuno-stained brain sections and three-dimensional whole mount preparations were evaluated for parasite localization and morphological alterations. Activation of choroidal and brain endothelial cells were characterized by flow cytometry. To evaluate the impact of early immune responses on CP and BMV, expression levels of inflammatory mediators, tight junctions (TJ) and matrix metalloproteinases (MMPs) were quantified. Additionally, FITC-dextran was applied to determine infection-related changes in BCSFB permeability. Finally, the response of primary CP epithelial cells to T. gondii parasites was tested in vitro. Results Here we revealed that endothelial cells in the CP are initially infected by T. gondii, and become activated prior to BBB endothelial cells indicated by MHCII upregulation. Additionally, CP elicited early local immune response with upregulation of IFN-γ, TNF, IL-6, host-defence factors as well as swift expression of CXCL9 chemokine, when compared to the BMV. Consequently, we uncovered distinct TJ disturbances of claudins, associated with upregulation of MMP-8 and MMP-13 expression in infected CP in vivo, which was confirmed by in vitro infection of primary CP epithelial cells. Notably, we detected early barrier damage and functional loss by increased BCSFB permeability to FITC-dextran in vivo, which was extended over the infection course. Conclusions Altogether, our data reveal a close interaction between T. gondii infection at the CP and the impairment of the BCSFB function indicating that infection-related neuroinflammation is initiated in the CP.

Early passage of Toxoplasma gondii across the blood–brain barrier

“…Thus, the CP tissue contained a higher relative foci density compared with the parenchymal and meningeal tissues and the vasculature. Interestingly, recent work reported that T. gondii infection of the CP entailed inflammatory responses and impaired B-CSF barrier function [43]. Jointly, this indicates that the CP constitutes a locus of passage by T. gondii, as shown for T. brucei [37,40].…”

The neuropeptide PACAP alleviates T. gondii infection-induced neuroinflammation and neuronal impairment

“…injection of cysts of the type II ME49 strain, previously harvested from brains of female NMRI mice infected i.p. with T. gondii cysts 6–12 months before, as described elsewhere [ 51 ]. Briefly, brains isolated from NMRI mice were mechanically homogenized in 1 ml sterile phosphate-buffered saline (PBS), and the number of cysts was determined in ≥ 80 µl homogenate using a bright field microscope.…”

Unveiling the gut-brain axis: structural and functional analogies between the gut and the choroid plexus vascular and immune barriers

“…In a previous work, ICAM-1 and VCAM-1 were described to be expressed exclusively in epithelial cells of the choroid plexus [ 129 ]. However, recent single cell analysis reported the expression of ICAM-1 and VCAM-1 transcripts in subclustered choroid plexus endothelial cells [ 120 , 135 ]. The presence of ICAM-1 and VCAM-1 adhesion molecules in the endothelium of the choroid plexus suggests a new role of the PVB in the immune modulation of the CNS.…”