Another novel finding was the identification of RV

Another novel finding was the identification of RV antigen in progenitor cells of outer granular layer of the brain. This cell type in the brain of CRS patients has not been previously known to be infected with rubella virus. However, the presence of unresolved outer granular layer and underdeveloped internal granular layer in a CRS case has been reported (Kemper et al., 1973). Mental retardation and microcephaly are frequently seen in infants with congenital rubella syndrome. In vitro studies suggested that the main cell type permissive to RV infection in developing brain tissue is the astrocyte (Chantler et al., 1995). Pathology studies of the brain of infants with congenital rubella syndrome revealed extensive degenerative changes in leptomeningeal and intrinsic SLx-2119 manufacturer and veins of the cerebrum. Vascular damage was associated with foci of necrosis localized in the deep white matter and gray nuclei, but no developmental malformations or significant inflammation of the nervous system was found (Rorke and Spiro, 1967; Rorke, 1973). During CNS development, multipotent neural stem cells give rise first to various kinds of specified precursor cells, which proliferate extensively before terminally differentiating into either neurons or glial cells. These progenitor cells migrate to different areas of the brain and are involved in normal development of the CNS. Thus, RV infection of progenitor cells could lead to a variety of malformations of the CNS, such as those found in CRS patients. Reports of congenital infection with other pathogens support the hypothesis that immature cells are apt to be target cells for infection in the developing brain (Feuer et al., 2003; Dietrich et al., 2004; Tsutsui et al., 2008). HSV, CMV, toxoplasmosis, and other infections are potent disrupters of fetal neurodevelopment leading to abnormalities in brain structure (e.g., hypoplasia of brain regions) and behavior disorders, including mental retardation and learning disabilities (Brown and Derkits, 2010). In a mouse model of fetal CMV infection neural stem progenitor cells in developing brains are the cell type that is most susceptible to CMV infection. The resulting disturbance of cellular events such as proliferation, differentiation and migration was suggested to be the main cause of CMV brain disorders (Tsutsui et al., 2008). Further studies are necessary to determine whether RV infection of neural progenitor cells has any effects on their proliferation, regeneration and differentiation. The histopathologic changes of DAD were observed only in Case 1. This infant had interstitial pneumonia and pulmonary hypertension, which frequently occur in CRS cases (Singer et al., 1967; Boner et al., 1983; Franklin and Kelley, 2001). Pulmonary arterial hypertension has been recently identified as the major contributor to mortality in CRS cases (Toizumi et al., 2014). We detected intense IHC staining in alveolar macrophages. We did not observe staining of alveolar epithelial cells, which were shown to be IHC positive in the rubella infected fetuses examined by Nguyen et al. (2015). Since RV infection in tissues is focal, and RV antigen is typically detected in a limited number of cells, the lack of immunostaining of alveolar epithelial cells in the present study might simply be due to the absence of infected cells in those lung sections that we were able to analyze. Another possibility is RV infection in alveolar epithelial cells or other cell types in the lung have been cleared, but RV antigen was still present in alveolar macrophages. It is currently unclear whether rubella virus replicates in macrophages. This study also identified capillary endothelial cells and the basal plate as the primary targets in the placenta. These data are in agreement with the results of one large study of placentas from CRS cases, in which rubella-specific immunofluorescence was detected in epithelial cells of chorionic blood vessels and amniotic epithelium; intracytoplasmic inclusion bodies (virions) were described in decidual cells in the basal plate and cytotrophoblasts (Garcia et al., 1985). Infection of endothelial cells can result in capillary necrosis and blockage of capillaries impacting placenta functions and leading to growth retardation of the fetus. Infection of endothelial cells may account for some of the vascular anomalies and viral spread, whereas infection of cells in the basal plate may lead to placental pathologies and thus account for the multitude of congenital malformations in CRS patients.