Abstract
Antigenic differences between bovine viral diarrhea virus (BVDV) vaccine strains and field isolates can lead to reduced vaccine efficacy. Historically, antigenic differences among BVDV strains were evaluated using techniques based on polyclonal and monoclonal antibody activity. The most common method for antigenic comparison among BVDV isolates is determination of virus neutralization titer (VNT). BVDV antigenic comparisons using VNT only account for the humoral component of the adaptive immune response, and not cell mediated immunity (CMI) giving an incomplete picture of protective responses. Currently, little data is available regarding potential antigenic differences between BVDV vaccine strains and field isolates as measured by CMI responses. The goal of the current paper is to evaluate two groups of cattle that differed in the frequency they were vaccinated, to determine if similar trends in CMI responses exist within each respective group when stimulated with antigenically different BVDV strains. Data from the current study demonstrated variability in the CMI response is associated with the viral strain used for stimulation. Variability in IFN-γ mRNA expression was most pronounced in the CD4+ population, this was observed between the viruses within each respective BVDV subgenotype in the Group 1 calves. The increase in frequency of CD25+ cells and IFN-γ mRNA expression in the CD8+ and CD335+ populations were not as variable between BVDV strains used for stimulation in the Group 1 calves. Additionally, an inverse relationship between VNT and IFN-γ mRNA expression was observed, as the lowest VNT and highest IFN-γ mRNA expression was observed and vice versa, the highest VNT and lowest IFN-γ mRNA expression was observed. A similar trend regardless of vaccination status was observed between the two groups of calves, as the BVDV-1b strain had lower IFN-γ mRNA expression. Collectively, data from the current study and previous data support, conferring protection against BVDV as a method for control of BVDV in cattle populations is still a complex issue and requires a multifactorial approach to understand factors associated with vaccine efficacy or conversely vaccine failure. Although, there does appear to be an antigenic component associated with CMI responses as well as with humoral responses as determined by VNT.
Highlights
Successful bovine viral diarrhea virus (BVDV) control strategies generally involve a multipronged approach that incorporates detection, intervention measures, and biosecurity [1]
A higher frequency of CD25+ (IL-2α receptor) labeling was observed on Peripheral Blood Mononuclear Cell (PBMC) (Table 2) for vaccinated calves in both Groups 1 and 2 and for all BVDV strains used for stimulation, and a lower frequency was observed for non-vaccinated calves
24 h after stimulation with BVDV, regardless of vaccination status or BVDV strain used for stimulation, minimal IL-2 mRNA expression was observed
Summary
Successful bovine viral diarrhea virus (BVDV) control strategies generally involve a multipronged approach that incorporates detection (testing/culling), intervention measures (vaccination), and biosecurity [1]. All approaches and implementation strategies should be considered to determine the most appropriate and cost-effective approach for each individual farm or entity as it relates to control programs. Understanding the reason for reduced vaccine protection is critical to the design of effective control programs. The highest BVDV prevalences were observed in countries that failed to implement any intervention strategy such as vaccination [2]. The goal of vaccination, as a method for controlling BVDV infections, is to reduce or prevent viremia in animals which subsequently may lead to prevention of fetal infections [3, 4]. Preventing viremia is critical for reducing transmission/shedding of the virus within a population of animals and reducing the impact of infection
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