Neuronal impairment following chronic Toxoplasma gondii infection is aggravated by intestinal nematode challenge in an IFN-γ-dependent manner

Abstract

Background It has become increasingly evident that the immune and nervous systems are closely intertwined, relying on one another during regular homeostatic conditions. Prolonged states of imbalance between neural and immune homeostasis, such as chronic neuroinflammation, are associated with a higher risk for neural damage. Toxoplasma gondii is a highly successful neurotropic parasite causing persistent subclinical neuroinflammation, which is associated with psychiatric and neurodegenerative disorders. Little is known, however, by what means neuroinflammation and the associated neural impairment can be modulated by peripheral inflammatory processes. Methods Expression of immune and synapse-associated genes was assessed via quantitative real-time PCR to investigate how T. gondii infection-induced chronic neuroinflammation and associated neuronal alterations can be reshaped by a subsequent acute intestinal nematode co-infection. Immune cell subsets were characterized via flow cytometry in the brain of infected mice. Sulfadiazine and interferon-γ-neutralizing antibody were applied to subdue neuroinflammation. Results Neuroinflammation induced by T. gondii infection of mice was associated with increased microglia activation, recruitment of immune cells into the brain exhibiting Th1 effector functions, and enhanced production of Th1 and pro-inflammatory molecules (IFN-γ, iNOS, IL-12, TNF, IL-6, and IL-1β) following co-infection with Heligmosomoides polygyrus . The accelerated cerebral Th1 immune response resulted in enhanced T. gondii removal but exacerbated the inflammation-related decrease of synapse-associated gene expression. Synaptic proteins EAAT2 and GABA A α1, which are involved in the excitation/inhibition balance in the CNS, were affected in particular. These synaptic alterations were partially recovered by reducing neuroinflammation indirectly via antiparasitic treatment and especially by application of IFN-γ-neutralizing antibody. Impaired iNOS expression following IFN-γ neutralization directly affected EAAT2 and GABA A α1 signaling, thus contributing to the microglial regulation of neurons. Besides, reduced CD36, TREM2, and C1qa gene expression points toward inflammation induced synaptic pruning as a fundamental mechanism. Conclusion Our results suggest that neuroimmune responses following chronic T. gondii infection can be modulated by acute enteric nematode co-infection. While consecutive co-infection promotes parasite elimination in the CNS, it also adversely affects gene expression of synaptic proteins, via an IFN-γ-dependent manner. Electronic supplementary material The online version of this article (10.1186/s12974-019-1539-8) contains supplementary materia...

Heligmosomoides bakeriandToxoplasma gondiico-infection leads to increased mortality associated with intestinal pathology

“…We also found that Hp burden was increased in HpTg animals. While others have not seen this, they have observed increased fecundity in the worms of the HpTg group [22],[94].…”

Influenza A virus (H1N1) infection induces microglia activation and temporal dysbalance in glutamatergic synaptic transmission

“…Interestingly, these results were apparent only at 14 dpi indicating once again temporary repercussions in the nervous system upon peripheral inflammation. In this regard, our group has previously shown the effects of neuroinflammation on synapse integrity [55,80]. Given the reduced expression of genes associated with synapse neurotransmission we decided to test for adverse effects of IAV infection on synapse integrity.…”

Protective immunity induced by CpG ODN‐adjuvanted virus‐like particles containing Toxoplasma gondii proteins

“…IFN‐γ and several other cytokines such as IL‐6 are required to regulate T. gondii tachyzoite proliferation in the brain through microglial activation 40 . The expression of these cytokines, though important for T. gondii clearance, comes at the cost of prolonged neuroinflammation which alters the structural integrity of the brain compartments 41 . To this extent, finding the level of pro‐inflammatory cytokine that ensures parasitic clearance while mitigating neuroinflammation is desired.…”