Background: Lymphatic tissues are the principle sites for HIV-1 replication, host-virus interaction and CD4+ T cell loss. However, the current understanding of the virus-host molecular interaction in lymphatic tissues, especially in early infection, is limited. We thus investigated virus-host interaction in the lymph nodes (LNs) of rhesus macaques during early simian immunodeficiency virus (SIV) infection.
Methods: Sixteen adult male macaques were intra-rectally inoculated with SIVmac251 (3.1 x 104 TCID50) and were euthanized at 3, 6, 10, 14 or 28 days post-inoculation (dpi); another 3 macaques were used as uninfected controls. Total RNA was isolated from rectal draining LNs of macaques and whole genome transcriptome was profiled using Illumina GAIIx, and genes with altered expression were identified and analyzed. SIV RNA in rectal draining LNs was quantified by using qRT-PCR and in situ hybridization (ISH). CD4+ and caspase-1+ cells in LNs were quantified using flowcytometry.
Results: SIV RNA was detected in all the animals euthanized at 6 and 10 dpi using both qRT-PCR and ISH, however, SIV RNA was only detected in 2 and 1 out of 3 animals at 3 dpi using qRT-PCR and ISH respectively. Transcriptome analysis showed that hosts had clear responses, with 103, 366 and 1350 differentially expressed genes (DEGs) at 3 dpi, 6 dpi and 10 dpi, respectively. Pathway analysis of DEGs at 6 dpi and 10 dpi pointed to the activation of pyroptosis in addition to innate immune response and inflammation pathways. Multiple genes in pyroptosis pathway were significantly up-regulated in expression. The active form of capase-1, the hallmark of pyroptosis activation, was quantified in CD4+ T cells in rectal draining LNs using flowcytometry. Concurrent with loss of CD4+ T cells in draining LNs after early infection, the level of caspase-1+ CD4+ T cells significantly increased, indicating that the pyroptosis mediated CD4+ T cell death occurs in vivo in early SIV infected lymphatic tissues.
Conclusions: This study shows robust host responses to early SIV infection, the activation of pyroptosis pathway, and CD4+ T cell loss mediated by pyroptosis in lymphatic tissues in vivo. Since CD4+ T cell loss and immune activation are the hallmarks of HIV pathogenesis, the CD4+ T cell loss mediated by pyroptosis and associated immune activation in vivo in early SIV infection identified in this study opens a new avenue to design interceptive strategy to prevent CD4+ T cell death.