The data presented here demonstrated that the HLA-G class I gene is unique among the members of the human class I gene family in that its expression is restricted to extraembryonic tissues during gestation. Furthermore, the pattern of HLA-G expression in these tissues changes as gestation proceeds. During first trimester HLA-G is expressed within the placenta and not within the extravillous membrane. At term, the pattern of the HLA-G expression is reversed, extravillous membrane expressed HLA-G while placenta does not. Another non-HLA-A, -B, -C class I gene, HLA-E, is also expressed by extraembryonic tissues. Unlike HLA-G, HLA-E is expressed by both placenta and extravillous membrane at first trimester and at term. These results raise the intriguing possbility that the HLA-G-encoded molecule has a role in embryonic development and/or the fetal-maternal immune response.
Bibliographical noteFunding Information:
This work was supported by Grant AI-18124 from the National Institutes of Health and by Grant IM-379D from the American Cancer Society.