Different genetic bases of immune responses in laying hens

Given the growing concerns of consumers regarding the safety of animal-derived foods, it is important to develop effective methods to reduce chronic use of antibiotics and to enhance the effectiveness of vaccine protection by improving, via genetic selection, the innate ability of birds to respond to antigenic challenges. Immune responses to different pathogens follow distinct pathways and resistance to most diseases and pathogens is controlled by polygenes. Therefore the aim of the work described in this thesis is to identify genetic factors underlying immune response in laying hens. The H/L population used in this study, originate from a cross of two lines divergently selected for high (H) and low (L) primary antibody response to Sheep Red Blood Cells (SRBC). Individuals from generations F0, F1 and F2 were genotyped with 180 microsatellite markers. The phenotypes were collected for entire F2 population with regard to several antigens: SRBC, KLH, E.coli, M.butyricum. The setup of the experiment allowed the use of two statistical models to analyze the data: a paternal half-sib model and a line-cross analysis model. In the half-sib analysis, QTL for the SRBC primary antibody response were identified on GGA1 and on GGA16. In the line-cross analysis Mendelian QTL were identified: on GGA4, GGA7, and GGA13. Subsequently, QTL analysis was performed on the data for two other antigens: KLH and M.butyricum. These analyses were performed on two independent populations: H/L cross and FP (feather pecking) lines. A QTL for the primary antibody response to KLH detected on GGA14 was validated in both populations under the half-sib analysis model. Based on the results differences in the genetic regulation of antibody responses to two different T-cell dependent antigens, KLH and M. butyricum were suggested. Subsequently the question asked was: which genetic components of innate immune responses are identified and which relations between the innate and the adaptive immune system could be found. Natural antibodies in our studies were measured by level of antibodies binding the homotopes LPS and LTA in the two, already mentioned populations: H/L and FP cross. For the H/L population data were collected at two ages: 5 wks of age and 18 wks of age, whereas for the FP cross data were collected at 37 wks of age. The QTL results indicate that different regions are associated with levels of antibodies binding the homotopes LPS and LTA, respectively, in poultry and that different genetic regions are involved in innate ( non specific ) and adaptive ( specific ) immune responses. The QTL region detected for primary antibody response to KLH on GGA14 was fine mapped. Previously collected genotypic data was combined with additional information obtained by genotyping individuals with SNP (Single Nucleotide Polymorphism) markers. A combined linkage disequilibrium / linkage analysis (LDLA) was performed. This analysis resulted in narrowing down QTL region from initial 50cM to the region below 1cM. Given the strong immuno-modulating features of KLH, and the high level of Nabs towards KLH in (non immunized) poultry we propose to focus on the QTL on GGA14 by future studies.