The pathogenesis of villitis of unknown etiology: Analysis with a new conjoint immunohistochemistry-in situ hybridization procedure to identify specific maternal and fetal cells

The conjoint immunohistochemistry-in situ hybridization (IHC-ISH) procedure permits, under routine light microscopic conditions, simultaneous documentation of either a male or female karyotype plus the immunological phenotype of individual cells within paraffin-embedded tissues. We have used this technique to characterize the inflammatory response in placental villitis of unknown etiology (VUE). A male placenta with severe VUE and appropriate control placentas were analyzed. In situ hybridization probes concurrently label both the X and Y chromosomes. On the same tissue section, individual cells were characterized with antibodies to CD3, CD68, or CD20. The amnion and syncytiotrophoblast were delineated by cytokeratin antibody (AE1/AE3). A complete karyotyping was performed on amnion cells to validate the procedure. Amnion cell karyotyping confirmed the accuracy of the procedure. The VUE case revealed that 88.8% of intravillous CD3+ lymphocytes were female (maternal), while 11.2% were male (fetal). Intervillous CD3+ lymphocytes and CD68+ macrophages were universally female. Intravillous CD68+ cells were only 10.5% female. Perivillous CD68+ cells were 94.6% female. Remarkably, multinucleated giant cells were exclusively maternal. This study confirms that lymphocytes in VUE are predominately but not exclusively maternal T cells. Our findings indicate that invasion of fetal villi by maternal T cells is associated with focal destruction of the syncytiotrophoblast, clarifying how placental immuno-defensive mechanisms may be contravened.