In addition to the unique allele number there are additional optional suffixes that may be added to an allele to indicate its expression status. Alleles that have been shown not to be expressed, 'Null' alleles have been given the suffix 'N'. Those alleles which have been shown to be alternatively expressed which may have the suffix 'L', 'S', 'C', 'A' or 'Q'.
The suffix 'L' is used to indicate an allele which has been shown to have 'Low' cell surface expression when compared to normal levels. The 'S' suffix is used to denote an allele specifying a protein which is expressed as a soluble 'Secreted' molecule but is not present on the cell surface. A 'C' suffix to indicate an allele product which is present in the 'Cytoplasm' but not on the cell surface. An 'A' suffix to indicate 'Aberrant' expression where there is some doubt as to whether a protein is expressed. A 'Q' suffix when the expression of an allele is 'Questionable' given that the mutation seen in the allele has previously been shown to effect normal expression levels.
As of April 2010, no alleles have been named with the 'C' or 'A' suffixes.
|HLA-A*24:09N||A Null allele|
|HLA-A*30:14L||An allele encoding a protein with significantly reduced or 'Low' cell surface expression|
|HLA-A*24:02:01:02L||An allele encoding a protein with significantly reduced or 'Low' cell surface expression, where the mutation is found outside the coding region|
|HLA-B*44:02:01:02S||An allele encoding a protein which is expressed as a 'Secreted' molecule only|
|HLA-A*32:11Q||An allele which has a mutation that has previously been shown to have a significant effect on cell surface expression, but where this has not been confirmed and its expression remains 'Questionable'|