Crimean-Congo hemorrhagic fever virus (CCHFV) is a bunyavirus causing severe hemorrhagic fever disease in humans, with high mortality rates. The requirement of a high-containment laboratory and the lack of an animal model hampered the study of the immune response and protection of vaccine candidates. Using the recently developed interferon alpha receptor knockout (IFNAR−/−) mouse model, which replicates human disease, we investigated the immunogenicity and protection of two novel CCHFV vaccine candidates: a DNA vaccine encoding a ubiquitin-linked version of CCHFV Gc, Gn, and N and one using transcriptionally competent virus-like particles (tc-VLPs). In contrast to most studies that focus on neutralizing antibodies, we measured both humoral and cellular immune responses. We demonstrated a clear and 100% efficient preventive immunity against lethal CCHFV challenge with the DNA vaccine. Interestingly, there was no correlation with the neutralizing antibody titers alone, which were higher in the tc-VLP-vaccinated mice. However, the animals with a lower neutralizing titer, but a dominant cell-mediated Th1 response and a balanced Th2 response, resisted the CCHFV challenge. Moreover, we found that in challenged mice with a Th1 response (immunized by DNA/DNA and boosted by tc-VLPs), the immune response changed to Th2 at day 9 postchallenge. In addition, we were able to identify new linear B-cell epitope regions that are highly conserved between CCHFV strains. Altogether, our results suggest that a predominantly Th1-type immune response provides the most efficient protective immunity against CCHFV challenge. However, we cannot exclude the importance of the neutralizing antibodies as the surviving immunized mice exhibited substantial amounts of them.IMPORTANCE Crimean-Congo hemorrhagic fever virus (CCHFV) is responsible for hemorrhagic diseases in humans, with a high mortality rate. There is no FDA-approved vaccine, and there are still gaps in our knowledge of the immune responses to infection. The recently developed mouse models mimic human CCHF disease and are useful to study the immunogenicity and the protection by vaccine candidates. Our study shows that mice vaccinated with a specific DNA vaccine were fully protected. Importantly, we show that neutralizing antibodies are not sufficient for protection against CCHFV challenge but that an extra Th1-specific cellular response is required. Moreover, we describe the identification of five conserved B-cell epitopes, of which only one was previously known, that could be of great importance for the development of diagnostics tools and the improvement of vaccine candidates.

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A genome wide search in European Wild Boar x Swedish Yorkshire (W x Y) inter-cross pigs has earlier identified quantitative trait loci (QTL) for leucocyte number and function on porcine chromosomes 1 and 8 (SSC 1 and 8). To verify the involvement of these chromosomal regions in the regulation of haematocrit (Hem) and haemoglobin (Hb) levels, leucocyte numbers and in vitro leukocyte functions (mitogen induced proliferation and IL-2 production, virus induced interferon-alpha production and neutrophil phagocytosis), animals of different genetic backgrounds were analysed. The animals comprised a back-cross sire family (n=47) of W x Y pigs and six crossbred [Y x Landrace (L)] sire families (n=191). They were genotyped for 16 genetic markers and an interval analysis was performed. On SSC1, a QTL close to S0082 on the q-arm that influenced numbers of white blood cells in L x Y pigs and numbers of band neutrophils and CD8(+) cells in W x Y pigs was identified (P

Genetic variation in total and differential white blood cell (WBC) counts, phagocytic capacity of polymorphonuclear leukocytes (PMNL), virus induced interferon-alpha (IFN-alpha) production, mitogen induced proliferation and interleukin 2 (IL-2) production of mononuclear cells (MNC) in vitro was studied in blood collected from 124 Yorkshire piglets, aged 8 weeks. The piglets were the offspring from 12 sires and 31 dams. Data from an earlier experiment, including 96 piglets of seven sires and 24 dams, were added when estimating heritabilities for Con A induced proliferation and IL-2 production. The highest heritability (h2 = 0.87 +/- 0.41) was estimated for the total number of PMNL. Medium high heritabilities (h2 = 0.3-0.4) were estimated for the phagocytic capacity of PMNL, Con A induced proliferation and IL-2 production and the total number of WBC, while the heritability estimates were lower (h2 = 0.00-0.08 +/- 0.12) for the total number of lymphocytes, serum concentrations of Ig and IFN-alpha production. Pronounced differences between litters from various dams were found for total number of lymphocytes, IFN-alpha production, Con A induced proliferation and IL-2 production. The Con A induced proliferation was positively correlated (r = 0.48, P < 0.001) with the IL-2 production and both these parameters were correlated (r = 0.44 and 0.37, respectively, P < 0.001) to the virus induced IFN-alpha production. Despite these positive correlations, no parental offspring group was uniformly superior across all traits measured. However, the heritabilities estimated for the immune parameters are sufficiently high to be used as genetic markers in selection for general immune competence of swine.

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