Table 1.

Autoimmunity can be a cause of PD.

Relationship	Research object	Evidence	References
Genetic regulation of autoimmunity in PD	PINK1, Parkin	Absence of PINK1/Parkin leads to the mitochondrial aberrations by triggering immune system disorders (reduced immuno-surveillance or activated autoimmunity).	(34, 43–47)
	DJ-1	Absence of DJ-1 leads to abnormal proliferation of nTregs and iTregs, and result in autoimmunity.	(48–50)
Pathogenic protein function in autoimmunity- associated PD	α-syn	Post-translational modifications and mutation of α-syn can be recognized as the autoantigen by the central immune system.	(56–58, 62, 64, 65)
Immune cells and autoimmunity in PD	DC	NM is an autoantigen released from dead DNs that stimulates the functional activation of DCs, triggering an autoimmune response and leading to microglial activation.	(28, 72–75)
	Microglia	Auto-aggressive loop initiated by DCs along with NM would be enhanced and amplified by microglial activation.	(78–80)
Clinical features and autoimmunity in PD	Tremor/dyskinesia/depression	Various autoantibodies have a strong positive correlation with these motor/non-motor symptoms.	(29, 83, 84)
	Constipation	Constipation is related to the gut dysbiosis and/or SIBO, which incurring the activation of enteric glial cells and contributing to the initiation of α-syn misfolding.	(90–93)
Other autoimmune diseases combined with PD	Hypothyroidism/hyperthyroidism/BP/SLE/ARD	Other autoimmune diseases may share genetic pathways with PD and are correlated closely with some clinical manifestations of PD.	(97–102)

PD, Parkinson's disease; α-syn, α-synuclein; DC, dendritic cell; NM, neuromelanin; SIBO, small intestinal bacterial overgrowth; BP, bullous pemphigoid; SLE, systemic lupus erythematous; ARD, autoimmune rheumatic disease.