Effect of Isoquinoline Alkaloid on PRRS Immune Response in Weaning Pigs

Porcine Reproductive and Respiratory Syndrome virus (PRRSv) has been reported to negatively modulate pig immune response, 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 use immuno-enhancer for PRRS immune response. Sangrovit Extra ®, a plant extract from Macleaya cordata, mainly consists of isoquinoline alkaloids (IQs). The IQs induced biological activities; anti-inflammatory, anti-microbial and immunomodulatory activities. The purpose of this study was to investigate the effect of IQs on serum neutralizing (SN) antibody titer and specific IFN-g producing peripheral blood mononuclear cells (PBMC) to PRRSv in weaning pigs in Thailand.

Twenty four, 21-day-old, male piglets, bought from a PRRS-free herd, were individually housed and divided into 4 groups, (n=6 per group); A (non-vaccinated, no challenged), B (non-vaccinated, with challenged), C (vaccinated, with challenged) and D (vaccinated, 100 ppm of IQs with challenged) groups. The C and D pigs were vaccinated with the PRRS vaccine (Ingelvac PRRS® MLV, BI, Germany) at 28 days of age. The B, C and D pigs 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 PBMC, measured by flow cytometry (BD AccuriTM C6).

The group D pigs (IQs 100 ppm) not only had the highest level of SN titer, in particular on D42 and D49, but also continuously increased percentage of specific IFN-g producing PBMC. Moreover, vaccinated pigs were found to have a higher level of both SN titer and the percentage of IFN-g producing PBMC than unvaccinated pigs. After the PRRSv challenge, percentage of specific IFN-g producing PBMC had increased drastically in vaccinated piglets compared to the slower response of SN titer.

Pigs fed Sangrovit Extra® supplemented feed enhanced both SN titer and specific IFN-g producing PBMC in PRRS vaccinated piglets compared to non-vaccinated pigs. In conclusion, the protective immune response to the PRRS infection should be focused more on IFN-g producing cells than the SN titer, particularly in vaccinated piglets.

Disclosure of Interest: None Declared.