"The HLA gene family provides instructions for making a group of related proteins known as the human leukocyte antigen (HLA) complex. The HLA complex helps the immune system distinguish the body's own proteins from proteins made by foreign invaders such as viruses and bacteria (U.S National Library of Medicine, 2016).” This is commonly referred to as tissue typing and is performed using a blood sample. HLA is also part of the major histocompatibility complex (MHC). See also MHC.
US National Library of Medicine. (2016). Genetics home reference. Author. Retrieved from: http://ghr.nlm.nih.gov/geneFamily/hla