Table 2 Common characteristics of the HLA-G, Paan-AG and Mamu-AG genes and their proteins

1. Limited polymorphism with only five functionally distinct HLA-G alleles and two Paan-AG alleles; 11 functionally uncharacterized Mamu-AG alleles identified so far.

2. Alternatively spliced mRNA that yields transcripts encoding multiple membrane-anchored and soluble protein isoforms

3. Truncation of the cytoplasmic tail due to the presence of a pre-mature stop codon in exon 6

4. High steady state levels of mRNA expression in the placenta and low expression in other tissues

5. Limitation of protein expression to very few tissues, notably the trophoblast cells in the placenta