Contribution of the genetic background to the immune response of broilers vaccinated or challenged with LPAI H9N2

BACKGROUND The knowledge on the immune responses to LPAI is limited. The purpose of this study was to investigate the immune responses of two divergently selected lines of broilers, a line responding with high antibody response to antigens (HH), and a line responding with low antibody titers (LL) to antigen. METHODS Day old chicks from each line were divided in two groups, one vaccinated with inactivated H9N2 vaccine and one non-vaccinated. At 21 days of age all the chicks were challenged with field isolate of H9N2, 1X106.5 ELD50 per chick by drops to the eye, nose and beak. Twenty four hours and 14 days post challenge (PC), the chickens were weighed blood spleen and lungs were taken and leukocytes were isolated. The leukocytes were stained with monoclonal antibodies for surface markers and analyzed by flow cytometry. We used Elispot assay to identify the number of antibody producing cells in each of the organs. mRNA was extracted using TRIsol reagent in order to assess the cytokine production level by qRT-PCR using the SYBR green methods. RESULTS Our results showed that LL-vaccinated group gained more weight than any of the other group. Using IDEXX kit, no antibody titers could be identified in vaccinated chicks 21 days post vaccination while 14 days PC vaccinated HH chickens demonstrated the highest average antibody titers. LL vaccinated chickens demonstrated higher average antibody titer than non-vaccinated LL. Using the Elispot assay no difference were found between the groups either cells producing IgA, IgM or IgY beside of a high number of IgY producing cells in the lungs of vaccinated HH birds. CONCLUSIONS Further data on leukocytes subpopulations using flow cytometry, cytokines production (IFNγ, IL-6, IL-18, IL-2 and IL-4) isotype specific antibody responses and number and functionality of NK cells are in process.