NKT cells are a distinct subset of lymphocytes with innate immune cell and T-cell characteristics, with immune regulation and antitumour effects.[25,26] Double negative NKT is a subset of NKT cells characterized by the expression of CD3 but not CD4 and CD8 co-receptors.[27] Although there are no studies supporting the association of NKT cells and CD3 with AN, some publications have reported their association with other psychiatric disorders such as depression, bipolar disorder, and post-traumatic stress disorder. This evidence concerns the gene CD4 and major depressive disorder.