Alzheimer's disease patients display neuropathological lesions, including the accumulation of amyloid-beta (Aβ) peptide and neurofibrillary tangles. Although the mechanisms causing the neurodegenerative process are largely unknown, increasing evidence highlights a critical role of immunity in the pathogenesis of Alzheimer's disease. In the present study, we investigated the role of regulatory T cells (Tregs) on Alzheimer's disease progression. First, we explored the effect of Tregs (CD4+CD25+ T cells) and Teffs (CD4+CD25− T cells) in an adoptive transfer model. Systemic transplantation of purified Tregs into 3xTg-AD mice improved cognitive function and reduced deposition of Aβ plaques. In contrast, adoptive transfer of Teffs diminished behavioral function and cytokine production. Next, we transiently depleted Treg population using an anti-CD25 antibody (PC61). Depletion of Tregs for four months resulted in a marked aggravation of the spatial learning deficits of six-month-old 3xTg-AD mice. Additionally, it resulted in decreasing glucose metabolism, as assessed by positron emission tomography (PET) with 18F-2 fluoro-2-deoxy-D-glucose ([F-18] FDG) neuroimaging. Importantly, the deposition of Aβ plaques and microglia/macrophage was increased in the hippocampal CA1 and CA3 regions of the Treg depleted 3xTg-AD compared to the vehicle-treated 3xTg-AD group. Our finding suggested that systemic Treg administration ameliorates disease progression and could be an effective Alzheimer's disease treatment.

Foxp3-expressing CD4+ regulatory T cells (Tregs) are vital for maintaining immune tolerance in animal models of various immune diseases. In the present study, we demonstrated that bee venom phospholipase A2 (bvPLA2) is the major BV compound capable of inducing Treg expansion and promotes the survival of dopaminergic neurons in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine mouse model of Parkinson’s disease. We associated this neuroprotective effect of bvPLA2 with microglial deactivation and reduction of CD4+ T cell infiltration. Interestingly, bvPLA2 had no effect on mice depleted of Tregs by injecting anti-CD25 Ab. This finding indicated that Treg-mediated modulation of peripheral immune tolerance is strongly involved in the neuroprotective effects of bvPLA2. Furthermore, our results showed that bvPLA2 directly bound to CD206 on dendritic cells and consequently promoted the secretion of PGE2, which resulted in Treg differentiation via PGE2 (EP2) receptor signaling in Foxp3−CD4+ T cells. These observations suggest that bvPLA2-CD206-PGE2-EP2 signaling promotes immune tolerance through Treg differentiation and contributes to the prevention of various neurodegenerative diseases, including Parkinson’s disease.

BackgroundAlzheimer’s disease (AD) is a severe neuroinflammatory disease. CD4+Foxp3+ regulatory T cells (Tregs) modulate various inflammatory diseases via suppressing Th cell activation. There are increasing evidences that Tregs have beneficial roles in neurodegenerative diseases. Previously, we found the population of Treg cells was significantly increased by bee venom phospholipase A2 (bvPLA2) treatment in vivo and in vitro.MethodsTo examine the effects of bvPLA2 on AD, bvPLA2 was administered to 3xTg-AD mice, mouse model of Alzheimer’s disease. The levels of amyloid beta (Aβ) deposits in the hippocampus, glucose metabolism in the brain, microglia activation, and CD4+ T cell infiltration were analyzed to evaluate the neuroprotective effect of bvPLA2.ResultsbvPLA2 treatment significantly enhanced the cognitive function of the 3xTg-AD mice and increased glucose metabolism, as assessed with 18F-2 fluoro-2-deoxy-D-glucose ([F-18] FDG) positron emission tomography (PET). The levels of Aβ deposits in the hippocampus were dramatically decreased by bvPLA2 treatment. This neuroprotective effect of bvPLA2 was associated with microglial deactivation and reduction in CD4+ T cell infiltration. Interestingly, the neuroprotective effects of bvPLA2 were abolished in Treg-depleted mice.ConclusionsThe present studies strongly suggest that the increase of Treg population by bvPLA2 treatment might inhibit progression of AD in the 3xTg AD mice.

α-Synuclein (α-Syn) has a critical role in microglia-mediated neuroinflammation, which leads to the development of Parkinson's disease (PD). Recent studies have shown that bee venom (BV) has beneficial effects on PD symptoms in human patients or 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) toxin-induced PD mice. This study investigated whether treatment with BV-derived phospholipase A2 (bvPLA2) would improve the motor dysfunction and pathological features of PD in human A53T α-Syn mutant transgenic (A53T Tg) mice. The motor dysfunction of A53T Tg mice was assessed using the pole test. The levels of α-Syn, microglia and the M1/M2 phenotype in the spinal cord were evaluated by immunofluorescence. bvPLA2 treatment significantly ameliorated motor dysfunction in A53T Tg mice. In addition, bvPLA2 significantly reduced the expression of α-Syn, the activation and numbers of microglia, and the ratio of M1/M2 in A53T Tg mice. These results suggest that bvPLA2 could be a promising treatment option for PD.

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