Partial Activation of natural killer and γδ T cells by classical swine fever viruses is associated with type I interferon elicited from plasmacytoid dendritic cells.

Vaccination with live attenuated classical swine fever virus (CSFV) vaccines can rapidly confer protection in the absence of neutralizing antibodies. With an aim of providing information on the cellular mechanisms that may mediate this protection, we explored the interaction of porcine natural killer (NK) cells and γδ T cells with CSFV. Both NK and γδ T cells were refractory to infection with attenuated or virulent CSFV, and no stimulatory effects, as assessed by the expression of major histocompatibility complex (MHC) class II (MHC-II), perforin, and gamma interferon (IFN-γ), were observed when the cells were cultured in the presence of CSFV. Coculture with CSFV and myeloid dendritic cells (mDCs) or plasmacytoid dendritic cells (pDCs) showed that pDCs led to a partial activation of both NK and γδ T cells, with upregulation of MHC-II being observed. An analysis of cytokine expression by infected DC subsets suggested that this effect was due to IFN-α secreted by infected pDCs. These results were supported by ex vivo analyses of NK and γδ T cells in the tonsils and retropharyngeal lymph nodes from pigs that had been vaccinated with live attenuated CSFV and/or virulent CSFV. At 5 days postchallenge, there was evidence of significant upregulation of MHC-II but not perforin on NK and γδ T cells, which was observed only following a challenge of the unvaccinated pigs and correlated with increased CSFV replication and IFN-α expression in both the tonsils and serum. Together, these data suggest that it is unlikely that NK or γδ T cells contribute to the cellular effector mechanisms induced by live attenuated CSFV.

Assessment of the phenotype and functionality of porcine CD8 T cell responses following vaccination with live attenuated classical swine fever virus (CSFV) and virulent CSFV challenge.

Vaccination with live attenuated classical swine fever virus (CSFV) induces solid protection after only 5 days, which has been associated with virus-specific T cell gamma interferon (IFN-γ) responses. In this study, we employed flow cytometry to characterize T cell responses following vaccination and subsequent challenge infections with virulent CSFV. The CD3(+) CD4(-) CD8(hi) T cell population was the first and major source of CSFV-specific IFN-γ. A proportion of these cells showed evidence for cytotoxicity, as evidenced by CD107a mobilization, and coexpressed tumor necrosis factor alpha (TNF-α). To assess the durability and recall of these responses, a second experiment was conducted where vaccinated animals were challenged with virulent CSFV after 5 days and again after a further 28 days. While virus-specific CD4 T cell (CD3(+) CD4(+) CD8α(+)) responses were detected, the dominant response was again from the CD8 T cell population, with the highest numbers of these cells being detected 14 and 7 days after the primary and secondary challenges, respectively. These CD8 T cells were further characterized as CD44(hi) CD62L(-) and expressed variable levels of CD25 and CD27, indicative of a mixed effector and effector memory phenotype. The majority of virus-specific IFN-γ(+) CD8 T cells isolated at the peaks of the response after each challenge displayed CD107a on their surface, and subpopulations that coexpressed TNF-α and interleukin 2 (IL-2) were identified. While it is hoped that these data will aid the rational design and/or evaluation of next-generation marker CSFV vaccines, the novel flow cytometric panels developed should also be of value in the study of porcine T cell responses to other pathogens/vaccines.