Early innate immune responses of Nile tilapia (Oreochromis niloticus) during tilapia lake virus (TiLV) infection

Immune responses to Tilapia lake virus infection: what we know and what we don’t know

“…Indeed, infiltration of mononuclear inflammatory immune cells into the CNS can occur days following neurotropic virus infections, with cells first accumulating in the perivascular areas, as also observed during TiLV infection in the brain (16, 90), followed by massive infiltration in the regions of virus infection, which has also been described during TiLV infection (32,42,82). Such a massive infiltration can drive the occurrence of lymphocytic meningitis, a condition often associated with brain inflammation, and which has also been described during TiLV infection (19).…”

“…Pathogenesis Syncytia formation (1,11,17,19,23,24,(35)(36)(37)43) Necrosis (1,13,19,21,24,31,32,35,37,42) Upregulation of genes involved in the regulation of necroptosis, in inflammation and in leukocyte migration (31) Infiltration of lymphocytic inflammatory cells in the brain, liver, intestines and spleen (19,21,32,35,42,43,82) Innate immunity Upregulation of tlr3, tlr7, tlr22 in tilapia and zebrafish (12)(13)(14)42) Upregulated expression of irf1, irf3, irf5, irf7 in tilapia and zebrafish (12-14, 31, 35, 43) Upregulated expression of rig-1 in zebrafish (12)(13)(14) Upregulated expression of mavs (ips-1) in tilapia (42) Upregulation of traf3 and nfkbia genes in tilapia (31) Upregulation of type I IFNs (ifnf1) in zebrafish and antiviral activity of type I IFN against TiLV infection (12)(13)(14) Upregulation of mxa gene transcripts in tilapia and zebrafish (12-14, 31, 32, 35) Upregulation of genes coding for mx1 and rsad2 (viperin) transcripts in brown trout and rainbow trout (15) Upregulation/high levels of IL-1b in tilapia and zebrafish (12-14, 31, 32, 35, 66, 67) Upregulation of il-8 in tilap...…”

Knowns and unknowns of TiLV-associated neuronal disease

“…Interestingly, syncytial formation has been observed in the brain tissue of tilapia experimentally infected with TiLV [ 64 , 106 , 107 ]. Moreover, inflammatory cell infiltration [ 9 , 11 , 12 ] 52 , 107 , 108 ] and brain haemorrhage [ 9 , 11 , 12 , 15 ] are amongst the pathological signs associated with TiLV disease in the brain.…”

“…In tilapia, multifocal areas of gliosis have been reported during TiLV infection [ 9 , 11 , 12 ][ 52 ]. Perivascular infiltrations of lymphocytic cells were reported in the brain of both experimentally and naturally infected tilapia [ 9 , 11 , 12 ][ 65 , 108 ], in addition to the presence of macrophage-like cells in basal regions of the brain [ 65 ]. In some cases, infiltrating inflammatory cells were localized to white matter [ 65 ].…”

“…Neuronal degeneration has been observed in the telencephalon (particularly in the optic lobes) of experimentally infected tilapia [ 9 ]. Localized blood clotting, suggestive of blood vessel rupture, has been reported in the brain cortex [ 108 ]. Multifocal cerebral, meningeal and leptomeningeal haemorrhages [ 9 , 11 , 13 , 14 ] and severe capillary congestion [ 9 , 12–14 ], 108 ] have also been observed, which are all suggestive of neurovascular injury and lesions in the CNS vasculature.…”