Uptake of pp65 in in vitro Generated pp65-Positive Polymorphonuclear Cells Mediated by Phagocytosis and Cell Fusion?

Objective: The cytomegalovirus (CMV) antigenemia consists of the detection of CMV pp65 in the nucleus of polymorphonuclear granulocytes (PMN), but it is unclear where and how PMN pick up virus particles or proteins. In an in vitro model for CMV antigenemia we investigated the mechanism of pp65 uptake by PMN that results in its expression in the nucleus. Methods: A series of inhibitors of different mechanisms was used to study the uptake of pp65 by PMN during coculture with CMV-infected endothelial cells and we performed a morphological analysis by light and transmission electron microscopy. Results: Nocodazole and cytochalasin B inhibited uptake of pp65 by PMN with 59.4 ± 14.1 and 73.3 ± 12.7%, respectively. The presence of anti-CMV hyperimmune globulin or lactoferrin during coculture reduced the number of pp65-positive PMN with 45.8 ± 7.0 or 40.6 ± 3.2%. Furthermore, a small number of the pp65-positive PMN obtained after coculture had fused to large cells with multilobed nuclei. PMN were observed that enclosed viral particles as well as free viral particles containing PMN in the cytoplasm. Conclusion: Fusion of viral particles with PMN and phagocytosis are both involved in the uptake of pp65.