Relative ability of different bovine leukocyte populations to support active replication of rinderpest virus

Inhibition of caspase-1-dependent apoptosis suppresses peste des petits ruminants virus replication

BACKGROUND

Peste des petits ruminants (PPR), caused by the PPR virus (PPRV), is an acute and fatal contagious disease that mainly infects goats, sheep, and other artiodactyls. Peripheral blood mononuclear cells (PBMCs) are considered the primary innate immune cells.

OBJECTIVES

PBMCs derived from goats were infected with PPRV and analyzed to detect the relationship between PPRV replication and apoptosis or the inflammatory response.

METHODS

Quantitative real-time polymerase chain reaction was used to identify PPRV replication and cytokines expression. Flow cytometry was conducted to detect apoptosis and the differentiation of CD4+ and CD8+ T cells after PPRV infection.

RESULTS

PPRV stimulated the differentiation of CD4+ and CD8+ T cells. In addition, PPRV induced apoptosis in goat PBMCs. Furthermore, apoptosis and the inflammatory response induced by PPRV could be suppressed by Z-VAD-FMK and Z-YVAD-FMK, respectively. Moreover, the virus titer of PPRV was attenuated by inhibiting caspase-1-dependent apoptosis and inflammation.

CONCLUSIONS

This study showed that apoptosis and the inflammatory response play an essential role in PPR viral replication in vitro, providing a new mechanism related to the cell host response.

Comparison of the Immunogenicities and Cross-Lineage Efficacies of Live Attenuated Peste des Petits Ruminants Virus Vaccines PPRV/Nigeria/75/1 and PPRV/Sungri/96

Despite the widespread use of live attenuated PPRV vaccines, this is the first systematic analysis of the immune response elicited in small ruminants. These data will help in the establishment of the immunological determinants of protection, an important step in the development of new vaccines, especially DIVA vaccines using alternative vaccination vectors. This study is also the first controlled test of the ability of the two major vaccines used against virulent PPRV strains from all genetic lineages of the virus, showing conclusively the complete cross-protective ability of these vaccines.

Peste des petits ruminants (PPR) is a severe disease of goats and sheep that is widespread in Africa, the Middle East, and Asia. Several effective vaccines exist for the disease, based on attenuated strains of the virus (PPRV) that causes PPR. While the efficacy of these vaccines has been established by use in the field, the nature of the protective immune response has not been determined. In addition, while the vaccine derived from PPRV/Nigeria/75/1 (N75) is used in many countries, those developed in India have never been tested for their efficacy outside that country. We have studied the immune response in goats to vaccination with either N75 or the main Indian vaccine, which is based on isolate PPRV/India/Sungri/96 (S96). In addition, we compared the ability of these two vaccines, in parallel, to protect animals against challenge with pathogenic viruses from the four known genetic lineages of PPRV, representing viruses from different parts of Africa, as well as Asia. These studies showed that, while N75 elicited a stronger antibody response than S96, as measured by both enzyme-linked immunosorbent assay and virus neutralization, S96 resulted in more pronounced cellular immune responses, as measured by virus antigen-induced proliferation and interferon gamma production. While both vaccines induced comparable numbers of PPRV-specific CD8⁺ T cells, S96 induced a higher number of CD4⁺ T cells specifically responding to virus. Despite these quantitative and qualitative differences in the immune responses following vaccination, both vaccines gave complete clinical protection against challenge with all four lineages of PPRV.

IMPORTANCE Despite the widespread use of live attenuated PPRV vaccines, this is the first systematic analysis of the immune response elicited in small ruminants. These data will help in the establishment of the immunological determinants of protection, an important step in the development of new vaccines, especially DIVA vaccines using alternative vaccination vectors. This study is also the first controlled test of the ability of the two major vaccines used against virulent PPRV strains from all genetic lineages of the virus, showing conclusively the complete cross-protective ability of these vaccines.

Use of SLAM and PVRL4 and identification of pro-HB-EGF as cell entry receptors for wild type phocine distemper virus

Signalling lymphocyte activation molecule (SLAM) has been identified as an immune cell receptor for the morbilliviruses, measles (MV), canine distemper (CDV), rinderpest and peste des petits ruminants (PPRV) viruses, while CD46 is a receptor for vaccine strains of MV. More recently poliovirus like receptor 4 (PVRL4), also known as nectin 4, has been identified as a receptor for MV, CDV and PPRV on the basolateral surface of polarised epithelial cells. PVRL4 is also up-regulated by MV in human brain endothelial cells. Utilisation of PVRL4 as a receptor by phocine distemper virus (PDV) remains to be demonstrated as well as confirmation of use of SLAM. We have observed that unlike wild type (wt) MV or wtCDV, wtPDV strains replicate in African green monkey kidney Vero cells without prior adaptation, suggesting the use of a further receptor. We therefore examined candidate molecules, glycosaminoglycans (GAG) and the tetraspan proteins, integrin β and the membrane bound form of heparin binding epithelial growth factor (proHB-EGF),for receptor usage by wtPDV in Vero cells. We show that wtPDV replicates in Chinese hamster ovary (CHO) cells expressing SLAM and PVRL4. Similar wtPDV titres are produced in Vero and VeroSLAM cells but more limited fusion occurs in the latter. Infection of Vero cells was not inhibited by anti-CD46 antibody. Removal/disruption of GAG decreased fusion but not the titre of virus. Treatment with anti-integrin β antibody increased rather than decreased infection of Vero cells by wtPDV. However, infection was inhibited by antibody to HB-EGF and the virus replicated in CHO-proHB-EGF cells, indicating use of this molecule as a receptor. Common use of SLAM and PVRL4 by morbilliviruses increases the possibility of cross-species infection. Lack of a requirement for wtPDV adaptation to Vero cells raises the possibility of usage of proHB-EGF as a receptor in vivo but requires further investigation.

Quantification and molecular characterization of the feline leukemia virus A receptor

Virus receptors and their expression patterns on the cell surface determine the cell tropism of the virus, host susceptibility and the pathogenesis of the infection. Feline thiamine transport protein 1 (fTHTR1) has been identified as the receptor for feline leukemia virus (FeLV) A. The goal of the present study was to develop a quantitative, TaqMan real-time PCR assay to investigate fTHTR1 mRNA expression in tissues of uninfected and FeLV-infected cats, cats of different ages, in tumor tissues and leukocyte subsets. Moreover, the receptor was molecularly characterized in different feline species. fTHTR1 mRNA expression was detected in all 30 feline tissues investigated, oral mucosa scrapings and blood. Importantly, identification of significant differences in fTHTR1 expression relied on normalization with an appropriate reference gene. The lowest levels were found in the blood, whereas high levels were measured in the oral mucosa, salivary glands and the musculature. In the blood, T lymphocytes showed significantly higher fTHTR1 mRNA expression levels than neutrophil granulocytes. In vitro activation of peripheral blood mononuclear cells with concanavalin A alone or followed by interleukin-2 led to a transient increase of fTHTR1 mRNA expression. In the blood, but not in the examined tissues, FeLV-infected cats tended to have lower fTHTR1 mRNA levels than uninfected cats. The fTHTR1 mRNA levels were not significantly different between tissues with lymphomas and the corresponding non-neoplastic tissues. fTHTR1 was highly conserved among different feline species (Iberian lynx, Asiatic and Indian lion, European wildcat, jaguarundi, domestic cat). In conclusion, while ubiquitous fTHTR1 mRNA expression corresponded to the broad target tissue range of FeLV, particularly high fTHTR1 levels were found at sites of virus entry and shedding. The differential susceptibility of different species to FeLV could not be attributed to variations in the fTHTR1 sequence.

Inhibition of host peripheral blood mononuclear cell proliferation ex vivo by Rinderpest virus

Rinderpest, or cattle plague, is caused by Rinderpest virus (RPV), which is related most closely to human Measles virus (MV), both being members of the genus Morbillivirus, a group of viruses known to have strong immunosuppressive effects in vitro and in vivo. Here, it was shown that peripheral blood mononuclear cells (PBMCs) isolated from cattle experimentally infected with either wild-type or vaccine strains of RPV impaired the proliferation of PBMCs derived from uninfected animals; however, in contrast to either mild or virulent strains of wild-type virus, the inhibition induced by the vaccine was both weak and transient. Flow-cytometric analysis of PBMCs obtained from cattle infected with different strains of RPV showed that the proportion of infected cells was virus dose-dependent and correlated with lymphoproliferative suppression.