**4. Anti-inflammatory cell-based strategy for Parkinson's disease therapy: Regulatory T-cells**

An anti-inflammatory strategy currently being studied as a cell-based therapy in PD involves the therapeutic introduction of Treg cells. It is now believed that Tregs suppress immune reactivity through multiple mechanisms, such as release of IL-10 and TGFβ, induction of apoptotic tolerance, and suppression of metabolic functions in effector immune cells such as microglia and effector T-cells. As the primary source IL10 and TGF1β *in vivo*, Tregs have been shown to be the major cells which regulate the inflammatory response in a number of disorders through their effects on the innate and adaptive immune responses that have escaped normal pathways of control. Recent studies using models of neurodegeneration demonstrated that induction of an anti-inflammatory Treg response inhibited microglial activation, and promoted neuronal survival (Reynolds, Banerjee et al. 2007; Liu, Gong et al. 2009; Reynolds, Stone et al. 2009). In another report, adoptively transferred Treg cells attenuated a Th17-mediated inflammatory response in mice that had been injected with MPTP and concomitantly vaccinated with nitrated (N) α-synuclein. In this model, injection of N-α-synuclein elicited an adaptive immune response in conjunction with the MPTP-induced neurotoxicity both of which were ameliorated by the transfer of natural or VIP-induced Treg cells in these mice (Reynolds, Stone et al. 2010). Tregs have also been shown to promote neurotrophic factor production from astrocytes (Reynolds, Banerjee et al. 2007; Reynolds, Stone et al. 2010), indicating their potential for neuroregeneration of DA neurons.

Strategies that use Th2 cells are also being employed. Th2 cells inhibit microglial cell activation through the production of IL4 and IL10, and stimulate the production of GDNF by astrocytes,

activated. These effects were mediated by inhibition of microglial cells since sinomenine failed to protect neuronal-cell enriched cultures which lacked microglia from MPP+ induced

Another plant extract, the flavonoid luteolin, has also been used for its anti-oxidant and anti-inflammatory properties. Luteolin was demonstrated to have neuroprotective effects by inhibiting oxidative stress-induced cell death in the DA-producing SH-SY5Y cell line (Kang, Lee et al. 2004). In mixed glial-neuron midbrain cell cultures from rats, luteolin attenuated the loss of TH+ DA-neurons after addition of increasing concentrations of LPS. The protective effect of luteolin in these experiments was shown to be mediated through the inhibition of microglial cell activation, and reduced production of TNFα, NO and ROS (Chen, Jin et al. 2008). Similarly, curcumin, the active anti-inflammatory isolate from turmeric (Curcuma longa), is known to have anti-inflammatory neuroprotective effects in CNS disorders. In an experimental allergic encephalomyelitis (EAE) mouse model of MS, curcumin inhibited EAE development by attenuating microglia activation and IL-12 production as well as Th1 cell differentiation (Natarajan and Bright 2002). Curcumin also has shown protective effects against LPS-induced DA neuron cell death in mixed rat neuron-glial cell cultures which were mediated by inhibition of the production of proinflammatory factors in microglia (Yang, Zhang et al. 2008). Taken together, the neuroprotective results from these three natural plant products suggest an interesting possibility for PD therapeutics. Since these and other similar plant-based isolates can cross the BBB and have anti-inflammatory as well as anti-oxidant properties, they may provide

**4. Anti-inflammatory cell-based strategy for Parkinson's disease therapy:** 

An anti-inflammatory strategy currently being studied as a cell-based therapy in PD involves the therapeutic introduction of Treg cells. It is now believed that Tregs suppress immune reactivity through multiple mechanisms, such as release of IL-10 and TGFβ, induction of apoptotic tolerance, and suppression of metabolic functions in effector immune cells such as microglia and effector T-cells. As the primary source IL10 and TGF1β *in vivo*, Tregs have been shown to be the major cells which regulate the inflammatory response in a number of disorders through their effects on the innate and adaptive immune responses that have escaped normal pathways of control. Recent studies using models of neurodegeneration demonstrated that induction of an anti-inflammatory Treg response inhibited microglial activation, and promoted neuronal survival (Reynolds, Banerjee et al. 2007; Liu, Gong et al. 2009; Reynolds, Stone et al. 2009). In another report, adoptively transferred Treg cells attenuated a Th17-mediated inflammatory response in mice that had been injected with MPTP and concomitantly vaccinated with nitrated (N) α-synuclein. In this model, injection of N-α-synuclein elicited an adaptive immune response in conjunction with the MPTP-induced neurotoxicity both of which were ameliorated by the transfer of natural or VIP-induced Treg cells in these mice (Reynolds, Stone et al. 2010). Tregs have also been shown to promote neurotrophic factor production from astrocytes (Reynolds, Banerjee et al. 2007; Reynolds, Stone et al. 2010), indicating their potential for

Strategies that use Th2 cells are also being employed. Th2 cells inhibit microglial cell activation through the production of IL4 and IL10, and stimulate the production of GDNF by astrocytes,

damage and death (Qian, Xu et al. 2007).

new directions for adjunct therapy.

neuroregeneration of DA neurons.

**Regulatory T-cells** 

thereby providing neuroprotection against MPTP-induced neuronal death (Benner, Mosley et al. 2004). Copaxone, a peptide-based therapy approved for patients with MS, is thought to promote the development of Th2 cells which function to decrease CNS inflammation through the release of anti-inflammatory cytokines and neurotrophic factors (Kipnis and Schwartz 2002; Angelov, Waibel et al. 2003; Benner, Mosley et al. 2004; Schwartz 2004). Copaxone-induced Tcells also have neuroprotective effects in animal models of ALS and PD (Angelov, Waibel et al. 2003; Benner, Mosley et al. 2004). However, because the interactions amongst regulatory T cells, glial cells, neurons and other infiltrating leukocytes within the SN is incredibly complex and not well understood, further studies to elucidate the regulatory pathways involved are necessary to develop Th2-cell based therapies for PD patients.
