Antiviral effect and BMAP28 induction by toll-like receptor 7 after bovine alpha-herpesviruses infection

BURUCÚA M; QUINTANA S; COBO E; POUZO L; ODEÓN A; PÉREZ S; MARIN M

Online

Simposio; Innate Immunity: Mechanisms and Modulation.; 2021

Keystone Symposia on Molecular and Cellular Biology

The cross-talk mechanisms between Toll-like receptors (TLRs) and cathelicidins that participate in airway epithelial host defenses remain undefined. TLR7 expression is differentially modulated by bovine herpesvirus (BoHV) 1 and 5 infection. This work investigated cathelicidin expression in the respiratory tract of BoHV-1- and 5-infected calves and whether TLR7 activation modulates cathelicidin expression and viral replication in bovine respiratory cells. BMAP28 expression was determined by RT-qPCR from nasal mucosa, tracheal epithelium and lung of infected calves [6 days post-infection (pi), n=4] relative to mock-infected animals (n=2). Primary cultures of fetal bovine lung were stimulated with TLR7 agonist (Imiquimod, 5 µg/mL) and infected 1h later with BoHV-1 or BoHV-5 (MOI: 0.1). Viral titers in supernatants and BMAP28 and TLR7 expression were determined at 6 and 24 hpi and analysed by t-test, Mixed Procedure of SAS, and REST software, respectively (P< 0.05). BoHV-5 infection decreased BMAP28 mRNA in nasal mucosa and lungs (0.27-fold and 0.07-fold, respectively). However, in tracheal epithelium, BMAP28 was only detected upon infection. In vitro TLR7 induction after BoHV-1 or BoHV-5 infection was higher in cells stimulated with Imiquimod (238-fold and 712-fold, respectively). At 24 hpi, Imiquimod had antiviral effect showing a significant decrease (P< 0.05) in viral replication (105.4 TCID50/mL) with respect to the control (106.6 TCID50/mL) and concomitantly up-regulation of BMAP28 in BoHV-5 infected-cells was observed (27-fold). Previously, we had found that in nasal mucosa and lung TLR7 expression is only induced by BoHV-1. Interestingly, we observed that cathelicidin decreases only during BoHV-5 infection. Overall, it is demonstrated that TLR7 activation has a protective effect and induces BMAP28 expression in bovine respiratory cells, suggesting a relevant interaction for controlling infection. Understanding about the modulation of the innate immune response given by TLRs, cathelicidins and their signalling pathways would be useful for preventive and therapeutic strategies against BoHV infections.