Intrastriatal injection of preformed alpha-synuclein fibrils alters central and peripheral immune cell profiles in non-transgenic mice

Parkinson's disease (PD) is characterized by the accumulation of alpha-synuclein (alpha-syn) inclusions, the major component of Lewy bodies. Extracellular alpha-syn aggregates act as a damage-associated molecular pattern (DAMP) and the presence of autoantibodies against alpha-syn species in the cerebrospinal fluid and the serum of PD patients implicate the involvement of innate and adaptive immune responses. In non-transgenic (Tg) mice, intrastriatal injection of preformed fibril (PFF) alpha-syn results in widespread pathologic alpha-syn inclusions in the CNS. While the PFF model has been broadly utilized to study the mechanistic relationship between alpha-syn transmission and other neuropathological phenotypes, the immune phenotypes in this model are not clearly demonstrated. This study aimed to characterize the immune phenotypes during pathologic alpha-syn propagation by utilizing PFF alpha-syn-injected non-tg mice. Here, we showed that pathologic alpha-syn inclusions are prevalent in various brain regions and the gut at 5 months post injection (p.i.), preceding the degeneration of dopaminergic neurons in substantia nigra (SN). We discovered a distinct inflammatory response involving both activation of microglia and astrocytes and infiltration of B, CD4+ T, CD8+ T, and natural killer cells in the brain at 5 months p.i. Moreover, PFF alpha-syn-injected mice display significant alterations in the frequency and number of leukocyte subsets in the spleen and lymph nodes with minimum alterations in the blood. Our data provide primary evidence that intracerebral-initiated synucleinopathies in non-tg mice alter immune cell profiles both in the CNS and peripheral lymphoid organs. Furthermore, our data provides support for utilizing this mouse model to assess the mechanistic connection between immune responses and synuclein pathology.