Immune responses of pigs after experimental infection with a European strain of Porcine reproductive and respiratory syndrome virus

Abstract

The purpose of this experiment was to study the immune response of pigs during an experimental infection with a European strain of Porcine reproductive and respiratory syndrome virus (PRRSV). Five pigs were challenged intranasally with PRRSV strain VP21 and another five were kept as controls. Clinical course and humoral and cell-mediated responses were monitored for 70 days post-infection (p.i.). Infected pigs developed mild signs at 24 h p.i. Viraemia was detectable by nested RT-PCR until day 14 p.i. Earliest seroconversions (ELISA) were seen by day 7 p.i. (three of five animals) and, by day 14, all inoculated pigs had seroconverted (ELISA and immunoperoxidase monolayer assay). Virus-neutralizing antibodies were undetectable until day 56 p.i. and, by day 70 p.i., two inoculated pigs still were negative. Flow-cytometry assays using peripheral blood mononuclear cells (PBMC) showed an upshift in CD8+ cells (day 7 p.i.) and a downshift of CD21+ cells (days 7 and 28 p.i.). Regarding cell-mediated responses, development of PRRSV-specific gamma interferon-secreting cells (IFN-γ-SC) and interleukin 4-secreting cells (IL4-SC) in PBMC was examined by ELISPOT assay. IFN-γ-SC were not detected significantly until day 14 p.i., whereas, for IL4-SC, no differences between groups were seen. Concurrently with the onset of viraemia and the development of clinical signs, serum haptoglobin levels and interleukin 10 (IL10) in PRRSV-stimulated PBMC-culture supernatants increased significantly. These differences disappeared later on. For IL2, IL4, IL8 or transforming growth factor beta, no differences were seen among groups. These results are compatible with a model in which the immune response does not fully control the outcome of the infection.

Longitudinal analysis of acute-phase proteins in saliva in pig farms with different health status

“…These results were similar to those obtained in experimental PRRS infections, where the highest levels of serum Hp were found at the time of seroconversion of pigs (4 times higher than those obtained at the beginning of the experiment; Díaz et al, 2005). Moreover, in previous field investigations, serum Hp levels were also markedly increased after exposure to the PRRSv in pigs at 8 to 10 weeks of age from a farm with chronic PRRSv infection (Asai et al, 1999).…”

“…Longitudinal studies have been used to assess the evolution of selected APP in serum at specific times during the clinical course of experimentally induced viral diseases such as African Swine Fever and Aujeszky's disease (Carpintero et al, 2007), PRRS (Díaz et al, 2005) and also in bacterial infections with Streptococcus suis (Sorensen et al, 2006), Haemophilus parasuis (Martín de la Fuente et al, 2009) or Actinobacillus pleuropneumoniae (Lauritzen et al, 2003). Under field conditions, APP have been monitored in pigs during the clinical course of post-weaning multisystemic wasting syndrome (PMWS; Grau-Roma et al, 2009) and in pigs with PRRS virus (PRRSv) chronic infections (Asai et al, 1999).…”

Development of an experimental inactivated PRRSV vaccine that induces virus-neutralizing antibodies

“…Virus-neutralizing (VN) antibodies against PRRSV protect against viremia, virus replication in lungs, transplacental spreading of the virus and reproductive failure [12][13][14]20]. However, VN antibodies only appear in low amounts around 4 weeks or more after PRRSV infection, which is in contrast with the fast appearance of high amounts of nonneutralizing antibodies [7,34]. Attenuated as well as inactivated PRRSV vaccines are frequently used in the field.…”

Pig Major Acute-Phase Protein and apolipoprotein A-I responses correlate with the clinical course of experimentally induced African Swine Fever and Aujeszky's disease

“…Research interest has been focussed on the study of pig APP response in experimental acute inflammation and bacterial infections, as well as in farm animal manipulations [7,18,21,28,31,39,42]. Although there have been studies about virus infections in pigs [2,11,35,38], little is known about the APP response elicited by these pathogens.…”

“…It has often been suggested that in humans, viral infections caused a weaker response compared to that of acute bacterial infections [41]. However, not much is known about APP response elicited by viruses in pigs [2,11,35,38]. The aim of this work was to give a general view of the APP response elicited during two relevant viral infections that have been extensively studied in swine: African swine fever (ASF) and Aujeszky's disease (AD).…”