Susceptibility of bovine antigen-presenting cells to infection by bovine herpesvirus 1 and in vitro presentation to T cells: Two independent events

The aim of the present study was to develop an in vitro system for presenta tion of bovine herpesvirus 1 (BHV-1) antigens to bovine T lymphocytes and t o characterize the antigen-presenting cells (APC) which efficiently activat e CD4(+) T cells. Two approaches were used to monitor the infection of APC by BHV-1 as follows: (i) detection of viral glycoproteins at the cell surfa ce by immunofluorescence staining and (ii) detection of UL26 transcripts by reverse transcription-PCR The monocytes were infected, while dendritic cel ls (DC) did not demonstrate any detectable viral expression. These data sug gest that monocytes are one site of replication, while DC are not. The capa cities of monocytes and DC to present BHV-1 viral antigens in vitro were co mpared. T lymphocytes (CD2(+) or CD4(+)) from BHV-1 immune cattle were stim ulated in the presence of APC previously Incubated with live or inactivated wild-type BHV-1. DC stimulated strong proliferation of Ag-specific T cells , while monocytes were poor stimulators of T-cell proliferation. When viral attachment to the surface of the APC was inhibited by virus pretreatment w ith soluble heparin, T-cell proliferation was dramatically decreased. Unexp ectedly, incubation of DC and monocytes with the deletion mutant BHV-1 gD(- /-), which displays impaired fusion capacity, resulted in strong activation of T lymphocytes by both APC types. Collectively, these results indicate t hat presentation of BHV-1 antigens to immune T cells is effective in the ab sence of productive infection and suggest that BHV-1 gD(-/-) mutant virus c ould be used to induce virus-specific immune responses in cattle.