One clinical trial documented that HBV was associated with an autoimmune disease in a small minority of subjects,15 and cytotoxic CD8+ T cells play a vital role in virus-induced neuroinflammation.16,17 Here, our data also showed that CD8+, not CD4+ T cells were detected in the third ventricle adjacent to the brain parenchyma in HBV mice, but not in PBS-treated mice (Supplementary Fig. 1E–L). Here, CD4 is linked to autoimmune disease.