Specific T-cell subsets have a role in anti-viral immunity and pathogenesis but not viral dynamics or onwards vector transmission of an important livestock arbovirus

Abstract

IntroductionBluetongue virus (BTV) is an arthropod-borne Orbivirus that is almost solely transmitted by Culicoides biting midges and causes a globally important haemorrhagic disease, bluetongue (BT), in susceptible ruminants. Infection with BTV is characterised by immunosuppression and substantial lymphopenia at peak viraemia in the host.MethodsIn this study, the role of cell-mediated immunity and specific T-cell subsets in BTV pathogenesis, clinical outcome, viral dynamics, immune protection, and onwards transmission to a susceptible Culicoides vector is defined in unprecedented detail for the first time, using an in vivo arboviral infection model system that closely mirrors natural infection and transmission of BTV. Individual circulating CD4+, CD8+, or WC1+ γδ T-cell subsets in sheep were depleted through the administration of specific monoclonal antibodies.ResultsThe absence of cytotoxic CD8+ T cells was consistently associated with less severe clinical signs of BT, whilst the absence of CD4+ and WC1+ γδ T cells both resulted in an increased clinical severity. The absence of CD4+ T cells also impaired both a timely protective neutralising antibody response and the production of IgG antibodies targeting BTV non-structural protein, NS2, highlighting that the CD4+ T-cell subset is important for a timely protective immune response. T cells did not influence viral replication characteristics, including onset/dynamics of viraemia, shedding, or onwards transmission of BTV to Culicoides. We also highlight differences in T-cell dependency for the generation of immunoglobulin subclasses targeting BTV NS2 and the structural protein, VP7.DiscussionThis study identifies a diverse repertoire of T-cell functions during BTV infection in sheep, particularly in inducing specific anti-viral immune responses and disease manifestation, and will support more effective vaccination strategies.

Immuno-informatics study identifies conserved T cell epitopes in non-structural proteins of Bluetongue virus serotypes: formulation of a computationally optimized next-generation broad-spectrum multi-epitope vaccine

“…( 25 – 27 ) suggest that epitopes from NS1, VP2 and VP7 proteins of BTV can induce cross-reactive CD4+ and CD8+ T cell responses against multiple BTV serotypes. Similarly, many other studies have demonstrated the importance of CD4+ and CD8+ T cells that recognize epitopes on structural (VP2 and VP7) and non-structural (NS1) BTV proteins in conferring protection against BT ( 23 , 24 , 28 – 30 ). In light of these findings, vaccination designed to elicit cross-reactive T cell responses holds the potential to protect animals against several BTV serotypes.…”

“…Notably, BTV infections elicit serotype-specific neutralizing antibodies primarily against the outer capsid, which exhibits significant variability across serotypes ( 29 , 39 ), prompting the exclusion of B cell epitopes in our broad-spectrum vaccine design. Furthermore, we selected the non-structural proteins of BTV as promising vaccine targets because they are highly conserved and are also the dominant source for T cell epitopes, particularly NS1 protein ( 1 – 3 , 8 , 10 , 11 , 13 , 15 – 19 , 21 , 22 , 24 , 27 , 30 , 33 – 36 , 38 – 87 ) ( 22 , 29 ). Additionally, we performed protein-protein docking and molecular dynamics simulations (MDS) to study the molecular interaction patterns and investigate the vaccine’s capacity to trigger an immune response.…”

Defining correlates of protection for mammalian livestock vaccines against high-priority viral diseases

“…The most-utilized CoPs are neutralizing antibody (Nab) titers, with higher antibody titers commonly linked to increased protection ( Figures 1E, F ). Reduced viral loads and the absence of clinical disease have consistently been associated with higher Nab titers following passive immunization or vaccination against FMDV (sheep, cattle, and pigs) ( 62 – 64 , 81 ), PRRSV ( 15 , 32 , 51 , 54 , 55 ), BTV ( 15 , 26 , 27 , 31 ), and CSFV ( 107 , 110 , 111 , 117 , 120 ) ( Table 1 ). Sterilizing immunity is associated with high Nab titers for PRRSV ( 54 , 186 ), CSFV ( 187 ), and BTV ( 188 , 189 ).…”

“…CD4+ T cells have a key role in generating strong protective humoral immunity through the development of T cell-dependent antibody responses against BTV ( 211 ), ASFV ( 212 ), and FMDV ( 213 ) and should be investigated for CSFV, PRRSV, and LSDV ( Table 1 ). Notably, the depletion of CD4+ helper T cells in sheep enhanced clinical signs of BTV primary infection and impaired the development of Nabs, thus highlighting the importance of these cells in the development of protective antibody-mediated immunity ( 31 ). The level of T-cell dependency for generating an antibody response is likely antigen dependent ( 31 ).…”

“…Notably, the depletion of CD4+ helper T cells in sheep enhanced clinical signs of BTV primary infection and impaired the development of Nabs, thus highlighting the importance of these cells in the development of protective antibody-mediated immunity ( 31 ). The level of T-cell dependency for generating an antibody response is likely antigen dependent ( 31 ). However, while BTV-specific CD4+ helper T-cell responses appear to be crucial in the development of a primary antibody response, CD4+ helper T cells were not activated/expanded in vitro following stimulation ( 180 ), and therefore may play a limited role in the memory response to challenge.…”