HLA stands for “human leu­ko­cy­te anti­gen.” It is found on the sur­face of white blood cells and most other cells in the body. It enab­les the immu­ne sys­tem to dis­tin­guish bet­ween its own and for­eign tis­sue. In the con­text of trans­plan­ta­ti­on, it plays a cru­cial role in tis­sue com­pa­ti­bi­li­ty. The HLA cha­rac­te­ris­tics are the­re­fo­re deter­mi­ned during typing.