Newcastle disease (ND), caused by infections with virulent strains of Newcastle disease virus (NDV), is one of the most important infectious disease affecting wild, peridomestic, and domestic birds worldwide. Vaccines constructed from live, low-virulence (lentogenic) viruses are the most accepted prevention and control strategies for combating ND in poultry across the globe. Avian macrophages are one of the first cell lines of defense against microbial infection, responding to signals in the microenvironment. Although macrophages are considered to be one of the main target cells for NDV infection in vivo, very little is known about the ability of NDV to infect chicken macrophages, and virulence mechanisms of NDV as well as the polarized activation patterns of macrophages and correlation with viral infection and replication. In the present study, a cell culture model (chicken bone marrow macrophage cell line HD11) and three different virulence and genotypes of NDV (including class II virulent NA-1, class II lentogenic LaSota, and class I lentogenic F55) were used to solve the above underlying questions. Our data indicated that all three NDV strains had similar replication rates during the early stages of infection. Virulent NDV titers were shown to increase compared to the other lentogenic strains, and this growth was associated with a strong upregulation of both pro-inflammatory M1-like markers/cytokines and anti-inflammatory M2-like markers/cytokines in chicken macrophages. Virulent NDV was found to block toll-like receptor (TLR) 7 expression, inducing higher expression of type I interferons in chicken macrophages at the late stage of viral infection. Only virulent NDV replication can be inhibited by pretreatment with TLR7 ligand. Overall, this study demonstrated that virulent NDV activates a M1-/M2-like mixed polarized activation of chicken macrophages by inhibition of TLR7, resulting in enhanced replication compared to lentogenic viruses.

The nutrient-sensing Target of Rapamycin complex 1 (TORC1) is an evolutionarily conserved regulator of longevity and healthspan. S6 kinase (S6K) is an essential downstream mediator for the effect of TORC1 on longevity. However, mechanistic insights on how TORC1-S6K signalling promotes lifespan and healthspan are still limited. Here we show that activity of S6K in the Drosophila fat body is essential for rapamycin-mediated longevity. Fat-body-specific activation of S6K blocked lifespan extension upon rapamycin feeding and induced accumulation of multilamellar lysosomal enlargements. By proteomics analysis we identified Syntaxin 13 (Syx13) as an important downstream mediator of TORC1-S6K signalling involved in regulating lysosomal morphology. Inhibition of TORC1-S6K signalling decreased age-associated hyperactivation of the NF-κB-like IMD pathway in the fat body and promoted bacterial clearance, mediated by Syx13, suggesting that lysosomal and immune function are connected during ageing. Middle-age-onset repression of IMD pathway in the fat body by Relish RNAi promoted bacteria clearance and extended fly lifespan. In mice, chronic rapamycin treatment elevated Syntaxin 12/13 (Stx12) level in liver. We identified alleviated immune processes in the aged liver as a common signature of S6K1-deficient and rapamycin-treated mice. Thus, our results indicate that suppression of the TORC1-S6K-Syx13 axis ameliorates both inflammageing and immunosenescence in hepatic tissues via the endolysosomal system and thereby extends longevity, providing a mechanistic explanation for the effects of rapamycin and suppression of S6K on immune function and lifespan in model organisms and, potentially, humans.