Replication complexes are membrane-bound cytoplasmic vacuoles involved in rubella virus (RV) replication. These structures can be identified by their characteristic morphology at the electron microscopy (EM) level and by their association with double-stranded (ds) RNA in immunogold labeling EM studies. Although these virus-induced structures bear some resemblance to lysosomes, their exact nature and origin are unknown. In this study, the localization of two lysosomal markers, lysosomal-associated membrane protein (Lamp-1) and acid phosphatase, relative to the replication complexes was examined by light and electron microscopy. Confocal microscopy using antibodies to dsRNA and Lamp-1 showed colocalization of these two markers in the cytoplasm of RV-infected cells. Immunogold labeling EM studies using antibodies to Lamp-1 confirmed that Lamp-1 was associated with RV replication complexes. EM histochemical studies demonstrated the presence of acid phosphatase in the vacuoles of RV replication complexes. Taken together, these studies show that RV replication complexes are virus-modified lysosomes.

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SUMMARY Rubella virus (RV) is the causative agent of the disease known more popularly as German measles. Rubella is predominantly a childhood disease and is endemic throughout the world. Natural infections of rubella occur only in humans and are generally mild. Complications of rubella infection, most commonly polyarthralgia in adult women, do exist; occasionally more serious sequelae occur. However, the primary public health concern of RV infection is its teratogenicity. RV infection of women during the first trimester of pregnancy can induce a spectrum of congenital defects in the newborn, known as congenital rubella syndrome (CRS). The development of vaccines and implementation of vaccination strategies have substantially reduced the incidence of disease and in turn of CRS in developed countries. The pathway whereby RV infection leads to teratogenesis has not been elucidated, but the cytopathology in infected fetal tissues suggests necrosis and/or apoptosis as well as inhibition of cell division of critical precursor cells involved in organogenesis. In cell culture, a number of unusual features of RV replication have been observed, including mitochondrial abnormalities, and disruption of the cytoskeleton; these manifestations are most probably linked and play some role in RV teratogenesis. Further understanding of the mechanism of RV teratogenesis will be brought about by the investigation of RV replication and virus-host interactions.