SIV EPITOPES AND GENETIC FACTORS THAT AFFECT SURVEILLANCE AND IMMUNITY ELICITED BY INFLUENZA VACCINES AGAINST EMERGING INFLUENZA STRAINS
Location: Virus and Prion Research Unit
Title: Comparison of Humoral and Cellular Immune Responses to Inactivated Swine Influenza Virus Vaccine in Weaned Pigs
Submitted to: Veterinary Immunology and Immunopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 2, 2011
Publication Date: August 1, 2011
Citation: Platt, R., Vincent, A.L., Gauger, P.C., Loving, C.L., Zanella, E.L., Lager, K.M., Kehrli, Jr., M.E., Kimura, K., Roth, J.A. 2011. Comparison of humoral and cellular immune responses to inactivated swine influenza virus vaccine in weaned pigs. Veterinary Immunology and Immunopathology. 142(3-4):252-257.
Interpretive Summary: Swine influenza is one of the top three disease concerns for the US pork industry. It is caused by swine influenza virus (SIV), a virus that has the ability to swap genes between different viruses if a pig is concurrently infected with two or more SIV isolates. This process is called reassortment. In the spring of 2009, a novel H1N1 influenza A virus began to spread among humans worldwide and led to declaration of a pandemic. The novel virus contained gene segments related to North American SIV lineages but had also reassorted and contained gene segments of Eurasian SIV lineages thus providing a unique genetic constellation. Although the new H1N1 has recently been demonstrated to be circulating among pigs, human infection was not connected to pig exposure. With previous introductions of human H1 influenza viruses into North American swine populations several different lineages of H1 influenza viruses now circulate in North American swine. This diversity complicates decisions on the best viruses to use for vaccines to protect pigs against SIV. Understanding how these different viruses induce immunity is important in terms of vaccine strain selection. In the study reported here, we examined antibody and cellular immune responses induced in pigs vaccinated with a previously circulating, human-like endemic SIV strain and how this vaccination affected challenge with a virus strain from the 2009 A/H1N1 pandemic. We found the vaccine induced antibodies only against the vaccine strain of influenza but we were able detect cellular immune responses against both viruses. The results for cellular responses demonstrate that the cellular immunity assay was sensitive and potentially detected a wider range of antigens that the pig's immune system recognizes than what is detected only by antibodies. These results will contribute to our basic understanding of how vaccines against influenza work in pigs.
Humoral and cellular immune responses to inactivated swine influenza virus (SIV) vaccine were evaluated and compared. Fifty 3-week-old weaned pigs from a herd free of SIV and PRRSV were randomly divided into the non-vaccinated control group and vaccinated group containing 25 pigs each. Pigs were vaccinated intramuscularly twice with adjuvanted UV-inactivated A/SW/MN/02011/08 (MN/08) H1N1 SIV vaccine at 6 and 9 weeks of age. Whole blood samples for multi-parameter flow cytometry (MP-FCM) and serum samples for hemagglutination inhibition (HI) assay were collected at 23 and 28 days after the second vaccination respectively. A standard HI assay and MP-FCM were performed against UV-inactivated homologous MN/08 and heterologous pandemic A/CA/04/2009 H1N1 (CA/09) viruses. While the HI assay detected humoral responses only to the MN/08 virus, the MP-FCM detected strong cellular responses against the MN/08 delta-cluster virus and lower but significant heterologous responses to the CA/09 gamma-cluster virus, especially in the CD4+CD8+ T cell subset. The cellular heterologous responses to UV-inactivated gamma-cluster virus by MP-FCM suggested that the assay was sensitive and potentially detected a wider range of antigens than what is detected by the HI assay. The MP-FCM also identified the responses of multiple parameters in different T cell subsets. Overall, the adjuvanted UV-inactivated A/SW/MN/02011/08 H1N1 SIV vaccine stimulated both humoral and cellular immune responses including the CD4-CD8+ T cell subset.