Secreted αsyn oligomers are toxic to neighboring cells. A) H4 cells were transfected with S1/S2 or mock transfectant. After 48 h, CM was collected and transferred to naive H4 cells. After 3 d incubation, caspase-3/7 activity is increased in S1/S2 CM-treated cells, which can be ameliorated by immunodepletion of αsyn. n = 5. B) Reduction of luciferase activity in S1/S2 CM after immunodepletion with Syn-1 antibody. n = 3. C) H4 cells were transfected with wt αsyn or mock transfectant. After 48 h, CM was collected and transferred to naive H4 cells. After 3 d incubation, caspase-3/7 activity is increased in wt αsyn CM-treated cells, which can be ameliorated by immunodepletion of αsyn. n = 5. D) Primary neurons were infected with AAV-V1S and AAV-SV2 or left naive. After 48 h, CM was collected and transferred to naive primary neurons. After 3 d incubation, caspase-3/7 activity is increased in V1S/SV2 CM treated cells, which can be ameliorated by immunodepletion of αsyn. n = 5. Data represent means ± se. *P < 0.05, ***P < 0.0001; unpaired t test with Welch's correction.