When patients with bipolar disorder are compared with healthy controls, increased percentages of activated T (i.e., CD3+/CD25+ and CD3+/CD71+) and B (CD19+) cells3 as well as a lower percentage of CD4+/CD25+/FOXP3+ Tregs but a higher percentage of CD8+/CD28− Tregs2 have been documented in different studies. This evidence concerns the gene CD4 and bipolar disorder.