Extracellular Vesicles from HTLV-1 Infected Cells Induce Secretion of Proinflammatory Cytokines in Recipient Blood Brain Barrier Cells

Abstract

Human T-cell leukemia virus type 1 (HTLV-1) is a blood-borne pathogen and incurable retrovirus that indiscriminately infects between 5-20 million individuals of all ages globally. Patients experiencing persistent high viral loads of  HTLV-1 have been associated with the development of the neurodegenerative disease known as HTLV-1-associated myelopathy (HAM)/tropical spastic paraparesis (TSP), a progressive disorder as a result of demyelination and cell death in the spinal cord, as well as disturbance to the Blood-Brain Barrier (BBB). Recently, the detection of HTLV-1 infected T cells and expanding populations of cytokines in cerebrospinal fluid (CSF) may suggest that HTLV-1 is immunopathologically mediated. Extracellular vesicles (EVs) are small nanoparticles that mediate cellular communication and inflammation. We recently found that EVs promote cell-to-cell contact, and consequently promote viral spread. In addition, we found that EVs containing the viral protein Tax are secreted from infected cells. Therefore, with this experiment, we aimed to elucidate the potential infiltration of varying HTLV-1 EV subpopulations across the BBB and into neural tissues including astrocytes, monocyte-derived macrophages, and neurons to better understand CNS related HTLV-1 pathogenesis. EVs were isolated from ATL-16 and HUT102 cells by collecting and centrifuging supernatants at 2,000 g (2K), 10,000 g (10K), and finally 100,000 g(100K).  Astrocytes (CCF-STTG1) elicited an increase in IL-8 post-treatment with 2k and 100k HTLV-1 EVs. EVs from THP-1 macrophages had high background levels of IL-8 which were enhanced with the treatment of 2k HTLV-1 EVs. However, IL-8 was not detected in HTLV-1 EV treated neurons (SHSY-5Y) and U937 macrophages. We suggest elevated levels of IL-8 in the BBB may be a result of astrocytic immune activation, which may be supported by existing macrophages.