Supplement to: Virulent African swine fever virus infection of porcine monocytes causes SLA I subversion due to loss of proper ER structure/function

African swine fever virus (ASFV) is a large DNA virus of the Asfarviridae family that causes a fatal hemorrhagic disease in domestic swine and wild boar. Infections with moderately virulent strains predominantly result in a milder clinical course and lower lethality. As target cells of ASFV, monocytes play a crucial role in triggering T-cell-mediated immune defense and ASF pathogenesis. We compared the effect of the highly virulent "Armenia2008" (ASFV-A) virus strain with that of the naturally attenuated "Estonia2014" (ASFV-E) on cellular immune activation in vivo and on primary monocytes ex vivo. Specifically, we asked whether antigen presentation of porcine monocytes is impaired upon ASFV-A infection. ASFV-A-infected monocytes are characterized by lower levels of swine leukocyte antigen (SLA) class I on the cell surface than ASFV-E-infected and uninfected monocytes. Despite stable steady-state SLA I mRNA/protein levels and expression of critical components of the antigen processing machinery, a marked decrease in maturation and reduced surface transport of SLA I were observed in ASFV-A-infected monocytes. The intracellular maturation block of SLA I was accompanied by a loss of functional rough ER structures and a pronounced formation of ER-associated aggresomes. This unsolved cellular stress resulted in a shutdown of overall host cell protein translation, mitochondrial dysfunction, and caspase-3-mediated apoptosis. In contrast, no such cellular subversion phenomenon was found in ASFV-E-infected monocytes. Our findings suggest that in domestic pigs infected with highly virulent ASFV-A, sequential subversion events occur in infected monocytes, likely leading to compromised T-cell activation and impaired downstream responses against ASFV.非洲猪瘟病毒（African swine fever virus, ASFV）是非洲猪瘟病毒科（Asfarviridae）的大型DNA病毒，可引发家猪与野猪致死性出血性疾病。中等毒力毒株感染后，临床进程通常更为温和，致死率也更低。作为ASFV的靶细胞，单核细胞在触发T细胞介导的免疫防御以及非洲猪瘟发病机制中发挥关键作用。本研究比较了高毒力毒株“Armenia2008”（ASFV-A）与自然减毒株“Estonia2014”（ASFV-E）在体内对细胞免疫激活的影响，以及二者对离体原代单核细胞的作用。具体而言，我们探究了猪单核细胞的抗原呈递功能在ASFV-A感染后是否受损。相较于ASFV-E感染组与未感染组单核细胞，ASFV-A感染组单核细胞表面的猪白细胞抗原（swine leukocyte antigen, SLA）I类分子表达水平更低。尽管ASFV-A感染组单核细胞的稳态SLA I mRNA与蛋白水平、以及抗原加工机制的关键组分表达均保持稳定，但我们仍观察到该组单核细胞的SLA I成熟过程显著受阻，且表面转运能力下降。SLA I的细胞内成熟阻滞伴随粗面内质网结构的功能丧失，以及显著的内质网相关聚集体形成。这种未被缓解的细胞应激最终导致宿主细胞整体蛋白翻译停滞、线粒体功能障碍，以及半胱天冬氨酸蛋白酶-3（caspase-3）介导的细胞凋亡。与之相反，ASFV-E感染组单核细胞未出现此类细胞劫持现象。本研究结果提示，在感染高毒力ASFV-A的家猪体内，受感染的单核细胞会发生一系列连续的细胞劫持事件，这可能会削弱T细胞激活，并损害机体针对ASFV的下游免疫应答。