B cells are also involved in the pathogenesis of PD, but are poorly understood and are still in the exploratory stage.[52,53] The BBB consists of vascular endothelial cells, basement membrane layer and astrocytes, which isolate the CNS from the peripheral circulation, preventing harmful substances from entering the brain.[54] Neuroinflammation in PD is often accompanied by disruption of the BBB when peripheral CD4+ T cells then enter the CNS and cause inflammation. The gene discussed is CD4; the disease is Parkinson disease.