THE ROLE OF INTERFERON AND NON-CONVENTIONAL T-CELLS IN THE CLEARANCE OF PRIMARY BHV-1 RESPIRATORY INFECTION

Bovine herpesvirus-1 (BHV-1) is prevalent globally and is an important cause of bovine disease. Humoral and cell-mediated immune responses contribute to viral clearance following a primary BHV-1 respiratory infection but innate immune mechanisms contributing to early control of BHV-1 infection are not known. Gene expression analyses and immunohistochemical (IHC) studies were used to investigate the role of interferons (IFNs) and innate immune cells during a primary BHV-1 infection. There was significant (P < 0.05) induction of type I IFN and IFN-stimulated genes (ISGs) in the URT within 3 days post-infection (pi) but virus shedding continued for another 4 to 7 days. In vitro studies demonstrated that both type I and II IFNs had limited capacity to inhibit BHV-1 replication and BHV-1 infection did not block ISG transcription. Consequently, immune cell recruitment to the URT was analyzed following BHV-1 infection to determine if alternative defence mechanisms were activated. Morphometric analyses of lymphocytes in URT tissues before and after BHV-1 infection revealed significant (P < 0.05) increases in cell populations expressing CD335+ (NKp46 natural cytotoxicity receptor), CD3+ (T-cell lineage marker) and CD8+ (cytotoxic T-cell marker) on day 5 pi. Confocal microscopy confirmed that approximately 90% of lymphocytes present on day 5 pi were T-cells co-expressing CD335 and CD8. This bovine T-cell subpopulation is known as non-conventional T cells, which may be innate lymphocytes. Specific recruitment of non-conventional T-cells to the site of BHV-1 infection in the URT raised questions regarding what chemokines may be involved in regulating this selective cell migration. Chemokine(s) involved in non-conventional T-cell recruitment in cattle are currently not known. qRT-PCR analysis of known bovine chemokine genes revealed that the expression of CCL4, CCL5 and CXCL9 genes were significantly (P < 0.05) up-regulated following BHV-1 infection in nasal turbinates. Thus, one or more of these chemokines may be involved in the selective recruitment of bovine non-conventional T-cells to the site of BHV-1 infection. The specific recruitment of non-conventional T cells to infected tissue suggests these cells may play an important role in either viral clearance or regulating host responses during BHV-1 infection