Parkinson’s disease (PD) is characterized by dopaminergic (DA) denervation of the striatum and progressive death of DA neurons in the substantia nigra pars compacta (SNpc) [
1]. Neuroinflammation has a role in several neurodegenerative diseases; though it may not be considered the primary cause, it contributes to the symptomatic phase [
2]. Several lines of research suggest that neuroinflammation is the major central event in dopaminergic neural cell death in PD [
3‐
5]. In postmortem SN from human PD brains, microglia results activated, lymphocytes are infiltrated [
2,
6], and in cerebrospinal fluids, there are high levels of pro-inflammatory cytokines such as tumor necrosis factor (TNF), cyclooxygenase-2 (COX-2), interleukin-1beta (IL-1beta), and IL-18 [
7,
8]. It has been suggested that in CNS neurodegeneration, neuronal damage may lead to the activation of microglia and astrocytes that in turn amplify the inflammatory response through chemokine secretion. This enhances CNS infiltration by peripheral immune cells. Studies in the acute neurotoxic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model provided evidences that neuroinflammatory processes can contribute to nigral DA neuronal death [
9‐
11]. Both the genetic deletions of microglial effectors [
12] and the suppression of T lymphocytes [
6] reduced neuronal loss suggesting that neuroinflammation in PD may actively participate in neuronal death. The “principal mechanism” that links the inflammatory response with neurodegeneration remains to be fully clarified. However, it is recognized that neuronal degeneration itself and in particular the accumulation and release of alpha-synuclein aggregates by the injured DA neurons early in the disease process [
13], may act as a signal, and can activate glial cells to produce and release a variety of pro-inflammatory molecules, exacerbating microglia activation and neuronal cell death [
14‐
18]. Within this scenario, the major players are the microglia, the reactive astrocytes, and the infiltrating monocyte-derived macrophages [
19]. Upon injury, activated M1-like microglia proliferates and participates in clearing cell debris in the early stages but may exacerbate brain injury through the production of neurotoxic substances, especially when it is overactivated for prolonged periods [
20]. In the M2-like phenotype, microglia has anti-inflammatory and neuron-reparative roles, protecting the damaged tissue by removing cell debris and releasing anti-inflammatory cytokines needed for tissue repair [
21]. Current treatments for PD are only symptomatic and have no effects on the ongoing neurodegeneration [
22]. The ideal therapeutic treatment for PD should have both symptomatic and restorative effects aimed at preserving midbrain DA neurons from degeneration [
23,
24]. In this sense, adult neural stem cells grafting into animal experimental models of neurodegenerative diseases have shown beneficial effects promoting both trophic and anti-inflammatory actions [
25‐
31]. Recently, we reported the therapeutic potential of erythropoietin-releasing neural precursors cells (Er-NPCs) intrastriatally infused in a preclinical model of PD, obtained upon the administration of MPTP [
30,
32]. After the unilateral transplantation into the striatum of MPTP-treated C57BL/6 mice, Er-NPCs were vital and capable of engrafting into the recipient’s brain. Er-NPC-treated animals improved their typical motor deficits within 3 days of cell transplantation, and this was accompanied by significant sparing of SN neurons. All these features and effects are likely dependent on erythropoietin’s (EPO) release since all of these were abolished by the co-injection of Er-NPCs with anti-EPO (aEPO) or anti-EPO-receptor (aEPO-R) antibodies. Little is known about the anti-inflammatory actions of Er-NPCs transplant in PD brains. Here, we focus on the study of this aspect and report that a rapid anti-inflammatory effect was evident 24 h after Er-NPCs transplant with the decrease of early pro-inflammatory cytokines mRNA levels (e.g., IL-1alpha, TNF). This effect was maintained for the following days, and IL-6 mRNA levels were significantly reduced as far as 7 days after transplantation. At the end of the 2-week observational period, histological data confirmed the reduction of activated microglia marker expression (GFAP and Iba1) and macrophages infiltration (CD68). Moreover, at the same time point, we observed the increase of markers associated with the M2-like protective phenotype. Co-injection of Er-NPCs with aEPO antibody neutralizes the Er-NPCs anti-inflammatory activity, strongly indicating that this effect is mediated by EPO released from Er-NPCs.