Associations of Polymorphisms in Four Immune-related Genes with Antibody Kinetics and Body Weight in Chickens

Four biological candidate genes, natural resistance associated macrophage protein 1 (SLC11A1 or NRAMP), prosaposin (PSAP), interferon Gamma (IFNG), and toll-like receptor 4 (TLR4), were examined to identify single nucleotide polymorphisms (SNP) and associations of the SNP with antibody response kinetics in hens. An $F_2$ population was produced by mating $G_0$ highly inbred (<99%) males of two MHC-congenic Fayoumi lines with highly inbred Leghorn hens. The $F_2$ hens (n = 158) were injected twice with SRBC and whole, fixed Brucella abortus (BA). Blood samples were obtained before each immunization, at 7 d after primary immunization, and at several time points after secondary immunization. Minimum titers (Ymin) and the time needed to reach them (Tmin), and maximum (Ymax) titers and the time needed to reach them (Tmax), were estimated from the seven post-secondary immunization titers using a nonlinear regression model. The $F_2$ hens were genotyped for the four candidate genes by using PCR-RFLP for one SNP per gene, which identified the parental allele. General linear models were used to test associations of SNP genotypes with antibody response parameters and BW measured at 4 ages. The IFNG SNP was highly significantly (p<0.0125) associated with primary response to SRBC, Tmin to BA, Ymin to BA, and 12-week BW. The current study demonstrated that the novel IFNG promoter SNP was associated with antibody kinetics for BA and SRBC in laying hens, and also with BW, suggesting that this cytokine may play a pivotal role in the relationship between immune function and growth.