Porcine Reproductive and Respiratory Syndrome Virus–Induced Immunosuppression Exacerbates the Inflammatory Response to Porcine Respiratory Coronavirus in Pigs

Abstract

We performed a comprehensive analysis of innate and adaptive immune responses in dual-virus infected pigs to understand whether a pre-existing immunomodulatory respiratory viral infection affects the overall immunity to a subsequent porcine respiratory coronavirus (PRCV) infection in pigs. Pigs were either mock-infected or infected with porcine reproductive and respiratory syndrome virus (PRRSV), a virus known to cause immunosuppressive respiratory disease, and then pigs were co-infected with PRCV, which normally causes subclinical respiratory infection. We collected samples for six independent experiments from 178 pigs that were also used for pathological studies. We detected a significant reduction in innate NK-cell-mediated cytotoxic function in PRRSV-infected pigs, which was synergistically further decreased in pigs co-infected with PRCV. Subsequently, in association with clinical signs we observed elevated levels of proinflammatory (IL-6), Th-1 (IL-12), and regulatory (IL-10 and TGF-β) cytokines. Increased frequencies of CD4CD8 double-positive T lymphocytes and myeloid cells, in addition to the elevated Th-1 and proinflammatory cytokines in dual-infected pigs, contributed to the severity of lung disease in pigs. The results of our study clarify how each virus modulates the host innate and adaptive immune responses, leading to inflammatory reactions and lung pathology. Thus measurements of cytokines and frequencies of immune cells may serve as indicators of the progression of respiratory viral co-infections, and provide more definitive approaches for treatment.

Adjuvant effects of invariant NKT cell ligand potentiates the innate and adaptive immunity to an inactivated H1N1 swine influenza virus vaccine in pigs

“…Homogenate (wt/vol) (lysate) of a piece of cranial lobe of the lung was prepared in DMEM containing antibiotics, aliquoted and stored at À80 C until used for virus detection (Khatri et al, 2010;Renukaradhya et al, 2010). Briefly, MDCK cells cultured in 96-well tissue culture plates were inoculated with serial 10-fold dilution of the lung homogenate in DMEM and supplemented with TPCK…”

“…Lung homogenate samples were subjected to cytokine analysis by ELISA (Khatri et al, 2010;Renukaradhya et al, 2010) to detect the levels of innate (IFN-a), proinflammatory (IL-6), Th1 (IFN-g and IL-12), and immunosuppressive [IL-10 and transforming growth factor b (TGF-b)] cytokines. Briefly, ELISA plates were coated with predetermined concentration of cytokine coating antibodies, IFN-a (Thermo Scientific), IFN-g (BD Biosciences), IL-6 and IL-12 (R&D Systems), IL-10 and TGF-b (Invitrogen) and incubated overnight at 4 C. Plates were washed and blocked and the test samples were added along with respective cytokine standards and incubated at RT.…”

“…Like humans, pig is a natural host for all three subtypes of influenza H1N1, H1N2, and H3N2 viruses. Pig has iNKT cell and CD1d transcripts, and recently iNKT cell in pig was discovered and its adjuvant effects to a model Ag was demonstrated using a-GalCer (Artiaga et al, 2014;Eguchi-Ogawa et al, 2007;Looringh van Beeck et al, 2009;Renukaradhya et al, 2010). Further, pigs genetically knocked out for CD1d were shown to be iNKT cell deficient (Yang et al, 2015).…”

Swine Influenza H1N1 Virus Induces Acute Inflammatory Immune Responses in Pig Lungs: a Potential Animal Model for Human H1N1 Influenza Virus

“…Lung lysates from all the euthanized pigs were prepared as described previously (3, 36) and frozen at Ϫ20°C until cytokine analysis by enzyme-linked immunosorbent assay (ELISA). Lung lysates were analyzed for innate (IFN-␣), proinflammatory (IL-6), Th2 (IL-4), Th1 (IFN-␥ and IL-12), and anti-inflammatory/T-regulatory (IL-10 and transforming growth factor ␤ [TGF-␤]) cytokines by ELISA as described previously (1,24,36).…”

Porcine reproductive and respiratory syndrome virus (PRRSV) up-regulates IL-15 through PKCβ1-TAK1-NF-κB signaling pathway

“…Previous reports have shown that blood NK cell cytotoxicity is suppressed with no appreciable changes in their frequency in blood after 8 days of PRRSV infected pigs Renukaradhya et al, 2010). Interestingly, we detected IL-15 mRNA level in PBMC at 7, 10, and 14 days after PRRSV-infected pigs (data not shown), finding that IL-15 was slightly up-regulated (about 2 fold) at 7 days after PRRSV-infected pigs, but IL-15 was suppressed at 10 and 14 days after PRRSV-infected pigs.…”