Virus-like particles in placentas from normal individuals and patients with systemic lupus erythematosus.

Nineteen human placentas, obtained from 9 normal women and 10 women with diagnosed systemic lupus erythematosus (SLE), were extensively examined by electron microscopy for the presence of virus-like particles. Free and budding viral forms were found in the placentas of 4 of the normal women and 3 of the women with SLE. In every case, these virus-like particles were found in the basal infoldings of the syncytiotrophoblast cells of the chorionic villi. These particles could be distinguished from typical mammalian type C viruses by the absence of a space between the envelope and the nucleocapsid.