Thioflavin-S (ThS) positive staining of endogenous α-syn aggregates. SH-SY5Y cells were infected with recombinant human α-syn short amyloid fibrils (SF: short amyloid fibrils of α-syn) and sub-passed at sixth passage (p6). The deposition and level of α-syn (red) in α-syn-infected cell lines after six passages were detected by anti-α-syn antibody (Additional file 6: Table S2). The colocalization was observed between the ThS signal (yellow) and anti-human α-syn antibody (red). The nuclei (blue) were stained with DAPI. Scale bars, 12 μm.