Moreover, focusing on adaptive immunity, the most studied loci in primary psychosis, especially in schizophrenia, are HLA- A, B, and C of the antigen-presenting Major Histocompatibility Complex (MHC), Class I and HLA-DRB1 and DQB1 of the MHC, Class II. Here, HLA-DRB1 is linked to schizophrenia.