1. Medawar PB. Some immunological and endocrinological problems raised by the evolution of viviparity in vertebrates. Symp Soc Exp Biol 1953; 44: 320–38
2. Johnson PM. Reproductive and maternofetal relations. In: Lachmann, PJ, Peters DK, Rosen FS, Walport MJ (eds), Clinical aspects of immunology, 5th edn, Oxford: Blackwell Scientific Publications, 1993: 755–67
3. Chumbley G, King A, Gardner L, Howlett S, Holmes N, Lokoe YW. Generation of an antibody to HLA-G in transgenic mice and demonstration of the tissue reactivity of this antibody. J Reprod Immunol 1994; 27: 173–86
4. Koller BH, Geraghty DE, Shimizu Y, DeMars R, Orr HT. HLA-E: a novel HLA class I gene expressed in resting T lymphocytes. J Immunol 1988; 141: 897–904
5. King A, Boocock C, Sharkey AM, Gardner L, Beretta A, Siccardi AG, Loke YW. Evidence for the expression of HLAA-C class I mRNA and protein by human first trimester trophoblast. J Immunol 1996; 156: 2068–76