PRRS Immune Response in Vaccinated and non-Vaccinated Naïve Pigs

Immuno-modulation of pig immune response to Porcine Reproductive and Respiratory Syndrome virus (PRRSv) infection has been reported, particularly the inhibition of interferon-g (IFN-g) and increasing the number of interleukin10 (IL-10) producing cells. Thus, one of the strategies in controlling the immune-modulation of PRRSv is to vaccinate piglets for PRRS immune response. The purpose of this study was to investigate the immune response using serum neutralizing (SN) antibody titer and specific IFN-g producing peripheral blood mononuclear cells (PBMC) to PRRSv in vaccinated and nonvaccinated naïve pigs in Thailand.

Eighteen, 21-day-old, male piglets, bought from a PRRS-free herd, were individually housed and divided into 3 groups, (n=6 per group); A (non-vaccinated, no challenged), B (non-vaccinated, challenged) and C (vaccinated with challenged) groups. The C group was vaccinated with the PRRS vaccine (Ingelvac PRRS® MLV, BI, Germany) at 28 days of age (D0). The B and C groups were challenged with 2 ml of field PRRSv (10⁵TCID₅₀/ml) and 10⁷TCID₅₀/ml intramuscularly on day 28 and 42 post vaccination, respectively. Blood samples were collected on day 0, 28, 35, 42 and 49 for serum neutralizing antibodies and PRRS-specific IFN-g-producing PBMCs, measured by flow cytometry (BD AccuriTM C6).

The SN titer response showed that non-vaccinated pigs had no response, meanwhile the vaccinated pigs had small response on D35 and stronger response after 2nd challenged. Moreover, the percentage of specific IFN-g producing PBMC had responded right after vaccination and drastically increase at the 1st challenged then recovered on D42. After the 2nd challenged, both B and C groups showed the same trend in response. No response in the negative group (A group).

The percentage of specific IFN-g producing PBMC, after PRRSv challenging, had increased drastically in vaccinated pigs compared to the slower response of SN titer. However, after the 2nd challenged, the response in specific IFN-g producing PBMC showed the same trend either vaccinated or non-vaccinated pigs, but not the same response in SN titer. In conclusion, the protective immune response to the PRRS infection should be intensively focused on IFN-g producing cells than the SN titer, particularly in vaccinated piglets.

Disclosure of Interest: None Declared.