The strong involvement of immune system in the epigenetic regulation of PRL under PCOS condition is further illustrated by Figure 2 where a remarkably distinct pattern of association is shown in the region of major histocompatibility complex (MHC) on band 6p21.3 of the short arm of chromosome 6, a region harbouring the human leukocyte antigen (HLA) genes (marked in red in Figure 2). This evidence concerns the gene PRL and polycystic ovary syndrome.