In Vitro Infectivity of HTLV-1 for Primary Rodent Lymphoid and Neuroglial Cells

Abstract

Human T lymphotropic virus type I (HTLV-1) has been associated with an adult T cell leukemia (ATL), sometimes disabling the immune system of an infected individual, or as a neurological disorder referred to as tropical spastic paraparesis (TSP) or HTLV-1 associated myelopathy (HAM). HTLV-1 predominantly infects T cells of the CD4+ subset, although in vitro infection of a number of diverse cell types has been observed. The susceptibility to HTLV- 1 infection of various neural cell types that could contribute to TSP/HAM pathogenesis has not yet been determined. The purpose of this study was to investigate HTLV-1 infectibility of various Fisher rat (F344) brain derived cells in vitro. Rat thymocytes isolated from Fisher rats were cocultivated with mitomycin C treated MT-2 cells giving rise to a transformed HTLV-1 infected and virus producing cell line, Rthy HT K1. HTLV-1 infection of the culture was confirmed by several assays. The rat and lymphoid origin of Rthy HT K1 was verified by detection of rat cell markers using FACS analysis. The infectivity of virions produced by Rthy HT K1 was demonstrated by subsequent infections of rat thymocyte cultures. Exposure of rat brain capillary endothelial cells to cell-free concentrated HTLV-1 or to mitomycin C treated HTLV-1 producing cells did not result in an infection detectable by p19 ELISA or p24. However, exposure of cultures containing neonatal rat astrocytes and oligodendrocytes to HTLV-1 using concentrated cell-free virus resulted in a transient production of p19. Astrocyte infection by HTLV-1 was further demonstrated by anti-p24 immunofluorescence, RT-PCR for tax mRNA and presence of viral particles by electron microscopy. Confirmation that the cell type infected by HTLV-1 was the astrocyte was achieved using dual-label immunofluorescence for anti-GFAP and HTLV- 1 anti-p24 and/or p19. It was observed that from days 2 to 7 post infection, the percentage of astrocytes infected increased from 11.6% to 27.4%. Subculturing of HTLV-1 infected astrocytes upon confluence about day 7 post infection resulted in a cessation of p19 production, while cultures not subcultured contained detectable levels of p19 until day 28. HTLV-1 pol DNA was detected within the HTLV-1 infected astrocytes despite the decline in p19 production. It was also noted that in the HTLV-1 infected cultures a population of cells became nonadherent. Dual-label immunofluorescence identified these cells as HTLV-1 infected astrocytes, indicating that HTLV-1 infection alters the adherence characteristics of astrocytes. HTLV-1 infection of oligodendrocytes was not observed. The ability of HTLV-1 to infect Fisher rat lymphocytes and astrocytes suggests it may serve as a useful animal model for investigating virus-host interactions in vivo, perhaps as a model for neurodegenerative disease.