Microchimerism (Mc) refers to harboring a small number of cells or DNA from a genetically distinct individual. During pregnancy Mc is naturally acquired in the exchange of cells between a mother and conceptus. In prior studies we found that a mother's cells persist in her progeny into adult life. During pregnancy a woman who is already host to Mc from her mother acquires an additional source of Mc as cells and cell-free DNA from the conceptus enter her circulation. These observations raise the question of whether HLA-relationships across generations influence the outcome of pregnancy in women and, as genetic diversity is generally thought to be good, whether excessive HLA-sharing across generations contributes to recurrent idiopathic pregnancy loss (RPL). HLA molecules are central to immune responses, to distinguishing self from "other" and extensive polymorphism is the hallmark feature of HLA genes. Due to the polymorphism in HLA genes most of the time there are numerous differences in HLA alleles among family members. However, occasionally an increase of HLA-sharing is observed in families, either due to HLA-homozygosity or heterozygous HLA-identity. Previous studies have suggested that excessive HLA-sharing of a woman and her partner is associated with idiopathic RPL, although studies have been conflicting. The first Specific Aim of this R21 proposal will test the hypothesis that HLA-relationships over three generations have less HLA-disparity (increased sharing) when women probands have primary idiopathic RPL compared to probands with a live birth and no history of miscarriage. HLA-genotyping will be conducted for DRB1, DRB3, DRB4, DRB5, DQA1, DQB1, A, B and C for women with primary idiopathic RPL, their mothers, conceptus, and partners. Specific Aim 2 will identify and quantify Mc from the proband's mother (MP-Mc) in consecutive blood samples from before, during and after pregnancy for probands with primary idiopathic RPL with a subsequent miscarriage or with a live birth and healthy women with no history of miscarriage. For this purpose a panel of HLA-specific and other genetic polymorphism specific quantitative PCR assays has been developed and will be employed to tested peripheral blood mononuclear cells. Specific Aim 3 will quantify Mc from the conceptus of the proband (CP-Mc) in the same peripheral blood samples using the same methods as in Aim 2 to test peripheral blood mononuclear cells as well as serum. In addition to the hypothesis of Aim 1, a second hypothesis will be tested in Aims 2 and 3, that dynamic changes in Mc, either MP-Mc or CP-Mc or both, is associated with idiopathic RPL. The consequences and long-term effects of harboring Mc from multiple sources are largely unknown as naturally acquired Mc from pregnancy has only recently been recognized. To our knowledge there are no prior studies investigating HLA-sharing or Mc across generations in idiopathic RPL. Harboring a small number of cells (or DNA) that originated from a genetically distinct individual is referred to as microchimerism (Mc). The finding that women harbor Mc from their own mothers and later acquire Mc from their own pregnancy(ies) raises questions about whether interactions between cell populations across generations sometimes influences pregnancy success. Because they help distinguish one cell from another particular genes, called HLA genes, are of special interest to investigate. [unreadable] [unreadable] [unreadable]