HLA

1:  the major histocompatibility complex in humans

2:  a genetic locus, gene, or antigen of the major histocompatibility complex in humans—often used attributively HLA antigens HLA typing; often used with one or more letters to designate a locus or with letters and a number to designate an allele at the locus or the antigen corresponding to the locus and allele relationship…between HLA-B27 antigen and ankylosing spondylitis—G. E. Ehrlich