FIG. 4.
Cytotrophoblasts (CTBs) and other cells show evidence of natural infection of chorionic villi with CMV in utero. Both floating villi (FV; A to C) and anchoring villi (AV; D) were studied. Tissues were analyzed by using immunolocalization techniques for expression of (A) cytokeratin (CK) and (B to D) CMV IE1/2 proteins. (B) In some cases, clusters of CMV-infected villous cytotrophoblast stem cells (CTBv; arrows) underlying the syncytium (ST, arrowheads) were the only sites of antibody reactivity. More often, numerous cells throughout the villi stained with anti-IE1/2 antibody. (C) In floating villi, nuclei of syncytiotrophoblasts, villous cytotrophoblasts, and stromal components expressed IE1/2 proteins. (D) The same pattern of immunoreactivity was seen in infected anchoring villi. Additionally, cytotrophoblasts in cell columns (CC) stained brightly. As a control, staining was performed as described for the experimental situation except that the primary or secondary antibody was omitted. No staining was detected (data not shown).