Background
The cell types that contribute to viral rebound after antiretroviral therapy interruption (ATI) in people living with HIV or experimental SIV-infected macaques are not well understood. Further, the mechanisms and impact of central nervous system (CNS) reservoirs in viral recrudescence after ATI remain unclear. Deep cervical lymph nodes (dCLN) drain the CNS, and productively SIV-infected macrophages have been reported to traffic from the CNS to the dCLN. Given this finding, we hypothesize that productively infected macrophages from the CNS contribute to the spread of infection after ATI.
Methods
We evaluated the cell types producing SIV in dCLN, axillary lymph nodes (AxLN), and mesenteric lymph nodes (MesLN) in three SIVmac251-infected rhesus macaques 14 days post-ATI. Animals were CD8-depleted before and during SIV-infection to increase the CNS reservoir. In tissue sections, viral RNA (vRNA) producing cells were detected using RNAscope in conjunction with CD3 and CD68 antibody staining, to identify T cells and macrophages, respectively. Additional sections were stained with antibodies directed against CD68 and Lyve-1, a marker for a subset of border-associated macrophages, to identify CNS-derived macrophages. Images were collected with a Nikon Ti-E microscope. Quantification of SIV vRNA+ CD68+ and SIV vRNA+ CD3+ cells was done with QuPath.
Results
At 14 days post-ATI, we found the majority of SIV-producing cells in LNs were CD3+ T cells. Importantly, CD68+ macrophages comprised a median of 46% (7-54%) of SIV-producing cells in dCLNs, while only 1.5% (0-11%) were detected in AxLN and 3.2% (0-3.5%) in MesLNs. CD68+ macrophages in the dCLN co-stained with the CNS macrophage marker Lyve-1.
Conclusions
These findings indicate that while most SIV-producing cells are T cells post-ATI, SIV-producing macrophages that traffic from the CNS to the dCLN are also a major contributor. These findings provide insights into HIV and SIV pathogenesis and may aid in the development of an HIV cure.
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