Glycoproteins derived from the major histocompatibility complex (MHC) class Ib gene, HLA-G, were first described in human placentas, where they were located in cytotrophoblast (CTB) cells within and adjacent to the maternal decidua. Despite nearly two decades of intensive research, the contributions of these proteins to semiallogeneic pregnancy remain poorly understood. The HLA-G gene has many novel features: the gene contains few polymorphisms in the coding region but multiple polymorphisms in the regulatory regions;at least 7 isoforms are generated by alternative splicing of mRNA derived from a single gene;restricted cell and tissue distribution of specific isoforms is a hallmark of the proteins. In this program application, three investigators from two institutions propose to study the role of placental HLA-G in pregnancy. All three, Dr. Joan Hunt (University of Kansas Medical Center, Kansas City, KS), Dr. Margaret Petroff from the same institution, and Dr. Carole Ober (University of Chicago, Chicago, IL) have extensive experience in reproductive immunology and have focused much of their research on MHC antigens in pregnancy. In Project I, Hunt will investigate regulatory mechanisms dictating expression patterns as well as specific functions of two of the soluble isoforms, HLA-G5 and HLA-G6, using newly developed recombinant HLA-G5 and -G6 and monoclonal antibodies to the proteins. In Project II, Petroff will examine the consequences of co-expression of HLA-G isoforms and members of the B7 family using stably transfected cells expressing various combinations of HLA-G/B7 proteins. In Project III, Ober will pursue functional aspects of HLA-G genotypes using newly developed allele-specific probes, and will explore relationships to diminished fertility. The program is supported by two Cores. Core A. Administration, directed by Hunt, will be responsible for assuring collection, integration and publication of the outcomes of the experiments. Core B Tissue Collection and Genotyping, directed by Ober, will collect and supply all investigators with early gestation tissues and tissues from certain types of problem pregnancies. This core will also identify polymorphisms in genes relevant to each project. The investigators in this program fully expect that their close and systematic collaboration will comprise a powerful approach to elucidating critical aspects of HLA-G expression, regulation and function, and will ultimately lead to new and improved therapies for impaired fertility. This research is highly relevant to public health. Approximately one in ten couples experiences fertility problems, and preterm labor is a common condition where pregnancy is terminated. Both conditions are costly in personal and financial terms.