HLA-G has many immune regulatory functions in pregnancy. First, HLA-G interact with the inhibitory receptors, immunoglobuline-like-transcript-2 and -4 (ILT-2 and ILT-4) expressed by a wide variety of immune cells especially monocytes, macrophages. The affinity of these receptors for HLA-G is higher than for other HLA class I molecules. In the same time, these receptors compete with CD8 in binding HLA-G, which could prevent activation of cytotoxic CD8 T cells, thereby contributing to the induction of tolerance. Furthermore, HLA-G has been shown to up regulate both ILT-2 and ILT-4, along with the killer-cell immunoglobulin-like receptor-2DL4 (KIR2DL4), on the surface of both antigen presenting cell, natural killer cells and CD4 T cells without preceding antigenic co-stimulation. This provides an interesting possibility that these receptors function at the materno-foetal interface by raising the treshold of the maternal immune system activation, thereby serving to induce tolerance.