An essential role for γ-herpesvirus latency-associated nuclear antigen homolog in an acute lymphoproliferative disease of cattle

Abstract

Wildebeests carry asymptomatically alcelaphine herpesvirus 1 (AlHV-1), a γ-herpesvirus inducing malignant catarrhal fever (MCF) to several ruminant species (including cattle). This acute and lethal lymphoproliferative disease occurs after a prolonged asymptomatic incubation period after transmission. Our recent findings with the rabbit model indicated that AlHV-1 infection is not productive during MCF. Here, we investigated whether latency establishment could explain this apparent absence of productive infection and sought to determine its role in MCF pathogenesis. First, whole-genome cellular and viral gene expression analyses were performed in lymph nodes of MCF-developing calves. Whereas a severe disruption in cellular genes was observed, only 10% of the entire AlHV-1 genome was expressed, contrasting with the 45% observed during productive infection in vitro. In vivo, the expressed viral genes included the latency-associated nuclear antigen homolog ORF73 but none of the regions known to be essential for productive infection. Next, genomic conformation analyses revealed that AlHV-1 was essentially episomal, further suggesting that MCF might be the consequence of a latent infection rather than abortive lytic infection. This hypothesis was further supported by the high frequencies of infected CD8 + T cells during MCF using immunodetection of ORF73 protein and single-cell RT-PCR approaches. Finally, the role of latency-associated ORF73 was addressed. A lack of ORF73 did not impair initial virus replication in vivo, but it rendered AlHV-1 unable to induce MCF and persist in vivo and conferred protection against a lethal challenge with a WT virus. Together, these findings suggest that a latent infection is essential for MCF induction.

The Pathology of Malignant Catarrhal Fever, With an Emphasis on Ovine Herpesvirus 2

“…30,33,41,138 The products of several open reading frames (ORFs) are used in transmission studies to establish whether latent or lytic infection patterns predominate in animals following challenge at different time points. 21,23,57,59,85,99,123 Expression in tissue of specific viral genes (in the case of OvHV-2, these include ORF9, DNA polymerase; ORF25, major capsid protein; ORF50, R-transactivator inducing latent to productive cycle switch; and ORF73, latency-associated nuclear antigen [LANA] homolog [genome maintenance protein]) is used to establish when productive infection occurs in the course of experimental infection. 21,23,99,139 Polyclonal antibodies to selected gene products have been used immunohistochemically to monitor infection.…”

Small RNA deep sequencing identifies viral microRNAs during malignant catarrhal fever induced by alcelaphine herpesvirus 1

“…1b), increased CD8 + T cell percentages in peripheral blood and LN (Fig. 1c), increased IFN-c production and characteristic infiltrations of lymphoblastoid cells in the perivascular spaces of many tissues (Palmeira et al, 2013). LCLs (also termed 'large granular lymphocytes') were established by culturing peripheral mononuclear cells in the presence of recombinant human IL-2 (hIL-2) (Swa et al, 2001).…”

“…Samples from an experiment previously described were used (Palmeira et al, 2013). Calves were experimentally infected with AlHV-1 WT C500 strain to induce MCF.…”

“…These lymphoblastoid cell lines (LCLs) can be used to amplify the number of infected cells in vitro. Although expression of latency-associated ORF73 expression has been shown to be essential for MCF induction (Palmeira et al, 2013), the actual mechanisms involved in the activation and proliferation of infected CD8 + T cells are yet to be identified. MCF can be experimentally induced in rabbits, where the observed lesions are indistinguishable from those described in MCF-susceptible species (Buxton & Reid, 1980).…”

“…The prevalence of AlHV-1 infection in wildebeest is close to 100 % and transmission to MCF-susceptible species is mainly believed to occur during the calving period and in the first months of life (Plowright, 1965a, b). Recent data demonstrated that MCF is caused by the activation and proliferation of latently infected CD8 + T cells, resembling a peripheral T cell lymphoma Dewals et al, 2008Palmeira et al, 2013). Infected lymphocytes collected from animals developing MCF can be propagated in vitro in the presence of interleukin 2 (IL-2) and display a 'large granular lymphocyte' phenotype (Swa et al, 2001).…”