The use of an avian macrophage-like cell line (HD11) transduced with recombinant lentiviruses to dissect the immunomodulatory role of Marek’s disease virus gene products

Marek's disease (MD) is caused by the highly contagious Marek's disease virus (MDV), a tumorigenic alphaherpesvirus. The disease is presently managed through vaccination. Nevertheless, the dynamic nature of MDV presents challenges, as new virulent strains may arise that can potentially overcome existing vaccine-mediated immunity. To address this, new and more effective vaccines are crucial. The immune system's first line of defense against infections is the innate immune response, where type I interferons (IFN-I) play a key role. As with other alphaherpesviruses, MDV encodes numerous genes capable of modulating IFN-I production during infection. Ablation of these genes in MDV could result in attenuation, thereby facilitating the creation of novel vaccine strains with augmented IFN-I induction during infection. Hence, a system to identify immunomodulatory MDV gene products that impede IFN-I production in avian innate immune cells is required. Herein, we present an innovative screening method that quantifies the expression of Interferon Omega 1 (IFNω1) in an avian macrophage-like cell line expressing MDV genes via recombinant lentivirus (rLV) integration. Five MDV gene products hypothesized to inhibit IFN-I production (Meq, US3, R-LORF4, UL46, and UL48) were assayed in our screening system. Stable expression of all MDV genes was obtained when rLV was utilized to insert these genes into HD11 cells. Additionally, we established the optimal conditions for activation of the IFN-I response in HD11 cells using a 2 kb double-stranded DNA segment delivered by transfection as a stimulant. With this approach, we demonstrated that these MDV gene products significantly decreased the gene expression of IFN-I when activated by transfection with double-stranded DNA.