TOLL-LIKE RECEPTOR 2 INFLUENCES THE SEVERITY OF NEUROPATHY DURING HERPES SIMPLEX VIRUS TYPE 1 INFECTION OF MURINE ENTERIC NERVOUS SYSTEM

INTRODUCTION: Recently, we have found that the neurotropic herpes simplex virus type 1 (HSV-1) establishes latency in rodent enteric nervous system (ENS), leading to gut dysmotility with no signs of illness, suggesting that may be involved in gastrointestinal motor disorders. AIMS&METHODS: Since the toll-like receptor (TLR) 2 contributes to antiviral innate immunity, this study aimed to assess the role of TLR2 on gut dysmotility and on ENS neurochemical changes induced at the early phase of HSV-1 infection. In C57/Bl6 mice (males, 10 weeks old) infection with HSV-1 was established by intranasal viral dose (103 pfu) followed 4 weeks (W) later by an intragastric inoculum (IG; 108 pfu). After 1-3W IG infection, in isolated ileum segments, changes in muscle tension were isometrically recorded following charbacol (0.001-30 μM) treatment and electric field stimulation (1-40 Hz). ENS neuropathy in whole mount preparations of ileal longitudinal muscle-myenteric plexus, immunostained with the neural markers HuC/D, peripherin and βIII-tubulin and with the glial marker S100β was assessed by confocal microscopy. Acetylcholinesterase (AChE) biochemical assay and nNOS (neuronal Nitric Oxide Synthetase), VIP, substance P (SP) and choline acetyltransferase (ChAT) immunohistochemistry were performed to evaluate alterations in the neurochemical coding. RESULTS: In vitro contractility studies have shown reduced muscarinic (Emax -35%) and nerve-mediated (-67% at 20 Hz) responses in WT post IG infection whereas in TLR2 KO were significantly increased by 23% and 51%, respectively. In the ENS of WT infected mice HuC/D and S100β immunoreactivities were drastically decreased whereas in TLR2 KO a higher S100β staining was observed. Neuronal integrity assessed by peripherin and βIII-tubulin immunofluorescence evidenced an irregular distribution more pronounced in infected TLR2 KO. In WT HSV-1 infection increased immunoreactivity of inhibitory nNOS+ and VIP+ neurons and decreased that of excitatory SP+. Furthermore, a reduced staining of AChE+ neurons, large fibers or small fibers, with an increased immunoreactivity of ChAT+ neurons was observed. Interestingly, opposite changes were found for these neurochemical markers in TLR2 KO. CONCLUSION: HSV-1 infection alters neuromuscular contractility, ENS integrity and neurochemical coding. TLR2 appears to be essentially involved in the severity of ENS neuropathy development. These results illustrate the complex but important roles that innate immune receptors play in host responses to HSV-1 during the early stages of ENS infection.