TNF-α and IL-10 differentially modulate apoptosis during PRRSV-1 infection of bone marrow- derived dendritic cells

Background Porcine reproductive and respiratory syndrome virus (PRRSV) modulates host immune responses, including apoptotic pathways, to facilitate infection. T Hypothesis/Objectives: This study examined the role of TNF-α and IL-10 in regulating apoptosis during PRRSV-1 infection of bone marrow-derived dendritic cells (BMDCs), using four isolates with distinct cytokine induction profiles. Methods Bone marrow–derived dendritic cells (BMDCs) from PRRSV-free piglets were produced and infected (0.1 MOI) in vitro with four well-characterized PRRSV-1.1 isolates differing in TNF-α and IL-10 induction: 3262 (TNF-α ⁺ /IL-10 ⁺ ), 3249 (TNF-α ⁺ /IL-10 ^- ), 2988 (TNF-α ^- /IL-10 ⁺ ), and 3267 (TNF-α ^- /IL-10 ^- ). In parallel, to dissect the role of TNF-α and IL-10, blockade experiments were performed in which BMDCs inoculated with the virus were cultured in the presence of excess TNF-α or IL-10 neutralizing antibodies. Apoptosis was assessed by annexin V/viability staining and cleaved caspase-3 detection using flow cytometry, with statistical analyses performed in GraphPad Prism. Results Early after infection (≤ 24 hpi), infected cells were predominantly non-apoptotic; by 48 hpi, apoptotic bystander cells increased markedly, consistent with extrinsic apoptosis. Neutralizing TNF-α in TNF-α-inducing isolates (3262, 3249) increased the proportion of infected cells and reduced bystander apoptosis, indicating that TNF-α limits viral spread via depleting susceptible cells. In contrast, IL-10 blockade in IL-10-inducing isolates (3262, 2988) increased non-apoptotic infected cells without altering overall infection frequency, suggesting that IL-10 promotes apoptotic progression in infected cells. Conclusion Collectively, these data indicate that TNF-α and IL-10 differentially modulate apoptotic outcomes during PRRSV-1 infection in an isolate-dependent manner.