TNF and Parkinson disease: Other proinflammatory proteins released from M1 cells (e.g., iNOS and TNF) also contribute to neurodegeneration in PD.173 Finally, Noelker et al. observed that TLR-4 knockout lowered the number of activated microglial cells and protected against SN dopaminergic degeneration, demonstrating that TLR-4 contributes to neuroinflammation.174 Adaptive immune responses also factor into neuroinflammation during PD.