Increased levels of major histocompatibility complex class II positive cells, including macrophages and microglia cells in the dorsomedial prefrontal cortex of MSA patients, can disrupt the BBB and attract CD4+ T-lymphocytes to the site of neuronal injury (20), which may lead to decreased CD3+ or CD4+ levels in the periphery. Here, CD4 is linked to multiple system atrophy.