(EDP Sciences, 2006) Bolea, Rosa; Monleón, Eva; Carrasco, Librado; Vargas, Antonia; Andrés Cara, Damián de; Amorena Zabalza, Beatriz; Badiola, Juan José; Luján, Lluís; IdAB. Instituto de Agrobiotecnología / Agrobioteknologiako Institutua
The aim of this work was to perform a complete study of maedi-visna virus (MVV)
infected mammary glands of naturally-infected sheep, and to determine if cells other than
macrophages undergo a productive viral infection in this organ. Fifteen seropositive and two
seronegative ewes were selected from MVV-infected flocks on the basis of clinical indurative
mastitis and three sheep from an MVV-free flock. Within the mammary gland, MVV-positive cells
were located by immunohistochemistry in the stroma and the epithelial alveolar barrier, most likely
the ovine mammary epithelial cells (OMEC) of the acini. In situ hybridization confirmed these
findings. Ultrastructural studies showed the presence of lentivirus-like particles budding off the cell
surface in the alveolar barrier and also free in the acinar lumen. The presence of mammary
histopathological lesions and MVV together with clear indications of productive infection
(demonstration of a cytopathic effect in OMEC cultures and infection of co-cultures) were observed
in the 15 seropositive and one of the seronegative sheep from the infected flock. These findings
demonstrate that the OMEC were infected in vivo and probably underwent productive infection when
studied ex-vivo. The OMEC of MVV-free sheep, which had subsequently been infected in vitro with
MVV, also showed productive infection when challenged in vitro, confirming the replication of MVV
in OMEC in vitro. The presence of MVV-infected OMEC in the mammary gland from infected
animals, the productive infection in these OMEC and the release of lentiviral particles to the acinar
lumen may have relevance in the pathogenesis and transmission of MVV infection.
