The pp38 Gene of Marek's Disease Virus (MDV) Is Necessary for Cytolytic Infection of B Cells and Maintenance of the Transformed State but Not for Cytolytic Infection of the Feather Follicle Epithelium and Horizontal Spread of MDV

Abstract

Marek's disease virus has a unique phosphoprotein, pp38, which is suspected to play an important role in Marek's disease pathogenesis. The objective of the present study was to utilize a mutant virus lacking the pp38 gene (rMd5⌬pp38) to better characterize the biological function of pp38. This work shows that the pp38 gene is necessary to establish cytolytic infection in B cells but not in feather follicle epithelium, to produce an adequate level of latently infected T cells, and to maintain the transformed status in vivo.The biological function of the Marek's disease (MD) virus (MDV) unique pp38 gene in the pathogenesis of MD is poorly understood. pp38 has been associated with lymphoid tropism (18), reactivation from latency (19, 21), maintenance of tumors (20), and immunosuppression (8). Three recombinant viruses (rMd5, rMd5⌬pp38, and rMd5/pp38CVI) were used in this work to expand the previous knowledge of the role of pp38 in viral replication and transmission, transformation and viral regulation of apoptosis, latency, reactivation, and cell cycle regulation. Construction of the recombinant viruses rMd5 and rMd5⌬pp38 has been described previously (15). The construction of rMd5/pp38CVI is described elsewhere (L. F. Lee, X. Cai, I. M. Gimeno, and S. M. Reddy, submitted for publication). Briefly, the RecA-assisted restriction endonuclease cleavage procedure was used to insert the pp38 gene from CVI988/Rispens at the same site that previously contained the Md5 pp38 gene, and insertion of the pp38 gene at the correct site was later confirmed by PCR and DNA sequencing. In vitro and in vivo expression of pp38 in rMd5/pp38CVI was confirmed by immunostaining with the monoclonal antibody T65 (L. F. Lee, unpublished data) that specifically reacts with CVI988/Rispens pp38.To study replication and transmission, 1-day-old 15x7 chickens (4) were inoculated with either rMd5, rMd5⌬pp38, or rMd5/pp38CVI. Horizontal virus transmission was monitored by using contact chickens. Samples of bursa, thymus, and spleen were collected at 3, 6, and 9 days postinoculation (dpi). At 26 dpi, samples of feather follicle epithelium (FFE) and spleens of contact chickens were collected. Monoclonal antibodies 1AN86.17 and T81 (17) specific to MDV glycoprotein B (gB) and ribonucleotide reductase (RR), respectively, were used to study MDV replication. At 6 dpi, late-antigen gB and early-antigen RR expression could not be detected in bursa of Fabricius, thymus, or spleen after inoculation with rMd5⌬pp38 (Fig. 1A), but both viral antigens were highly expressed in all tested chickens following rMd5 or rMd5/pp38CVI inoculation ( Fig. 1C and E). The failure of rMd5⌬pp38 to induce cytolytic infection was cell type specific because B lymphocytes but not FFE were affected (Fig. 1B, D, and F). Horizontal virus transmission was confirmed by isolating MDV from every contact chicken (data not shown).To study the effect of the pp38 gene on transformation and apoptosis, two experiments were conducted. In experiment 1, 1-day-old 15x7 chickens (4) were inoculated ...

Homodimerization of Marek's Disease Virus-Encoded Meq Protein Is Not Sufficient for Transformation of Lymphocytes in Chickens

“…For example, disruption of pp38, vIL8, or LORF11 genes from oncogenic MDV resulted in reduced tumor incidence as a consequence of impaired lytic replication in chickens (6,9,19,27). On the other hand, disruption of vTR (viral telomerase RNA) or meq gene did not appear to have an effect on lytic replication in vivo but resulted in 60 and 100% reductions in tumor incidence, respectively (25,36).…”

Mortality of One-Week-Old Chickens During Naturally Occurring Marek’s Disease Virus Infection

“…11 Both cytoplasmic and nuclear pp38 antigen was found in our birds. Previous studies describe and illustrate immunopositivity in the bursa of Fabricius of chickens experimentally infected with MDV.…”

“…Pp38 is an early protein of MDV and is highly specific to MDV. 4,11 It is necessary for MDV cytolytic infection of B cells and maintenance of the transformed status of lymphocytes by preventing apoptosis.…”

MicroRNA Profile of Marek's Disease Virus-Transformed T-Cell Line MSB-1: Predominance of Virus-Encoded MicroRNAs

“…Some of the functions of Meq associated with oncogenic properties, such as its interaction with CtBP, parallel those of other viral oncogenic sequences, such as adenovirus E1A and Epstein-Barr virus (EBV) nuclear antigens EBNA3A and -3C (6), highlighting the convergent evolution of oncogenic pathways in these viruses. Recent studies have also identified the role of other genes, such as the pp38 (23), viral interleukin-8 (vIL-8) (49), ICP4 (15,38), R-LORF4 (33), UL36 (32), and MDV-encoded telomerase RNA (22,63) genes, in pathogenesis.…”