A previous study has shown that APRIL enhances midbrain dopaminergic axon growth and nigrostriatal projection.64 Dysregulation of BAFF/APRIL has been implicated in autoimmune disease, cancer, as well as PD.65 Together with reduced levels of two other TNF superfamily members, BAFF and CD40L, our findings may suggest suppressed central relatively to peripheral regulating network for B cell proliferation, survival, and antibody production, particularly in LRRK2 carriers. Here, CD40LG is linked to Parkinson disease.