FIGURE 1.

HLA nomenclature with allele resolution at four fields (eight digits). Commonly, the HLA prefix followed by gene name and four fields of the allele. The suffix may be added to an allele to indicate its expression status as low cell surface expression “L”, soluble secreted molecule, “S”, present in the cytoplasm, “C”, aberrant. “A”, questionable, “Q” or not expressed as null alleles “N”. The ambiguous allele typing for identical nucleotide sequences are coded as “G” after first three allele fields, and for identical protein sequences as “P” after two allele fields designation for exons encoding peptide binding domains (exon 2 and 3 for HLA-class I, and exon 2 only for HLA-class II alleles) (adapted from http://hla.alleles.org).