Selective breeding for high natural antibody level increases resistance to avian pathogenic Escherichia coli (APEC) in chickens

Keyhole limpet hemocyanin (KLH)-binding natural antibody (NAb) titers in chickens are heritable, and higher levels have previously been associated with a higher survival. This suggests that selective breeding for higher NAb levels might increase survival by means of improved general disease resistance. Chickens were divergently selected and bred for total NAb levels binding KLH at 16 weeks of age for six generations, resulting in a High NAb selection line and a Low NAb selection line. To for test differences in disease resistance, chickens were challenged with avian pathogenic Escherichia coli (APEC) in two separate experiments. Chickens at 8 days of age received one of four intratracheal inoculations of 0.2 mL phosphate buffered saline (PBS): 1) mock inoculate, 2) with 0.2 mL PBS containing 10^8.20 colony-forming units (CFU)/mL APEC, 3) with 0.2 mL PBS containing 10^6.64 CFU/mL APEC, and 4) with 0.2 mL PBS containing 10^7.55 CFU/mL APEC. Mortality was recorded during 7 days post inoculation. Overall, 50-60% reduced mortality was observed in the High line compared to the Low line for all APEC doses. In addition, morbidity was determined of the surviving chickens at 15 days of age. The High line had lower morbidity scores compared to the Low line. We conclude that selective breeding for high KLH-binding NAb levels at 16 weeks of age increase APEC resistance in early life. This study and previous studies support the hypothesis that KLH-binding NAb might be used as an indicator trait for to selective breed for general disease resistance in an antigen non-specific fashion.

Effects of early life dextran sulfate sodium administration on pathology and immune response in broilers and layers

Intestinal pathology early in life may affect immune development and therefore immune responses later in life. Dextran sulfate sodium (DSS) induces colitis in rodents and is a widely used model for inflammatory bowel diseases. The present study investigated DSS as a model for early life intestinal pathology and its consequences on intestinal pathology, ileal cytokine, and immunoglobulin mRNA expression levels as well as the antibody response towards an immunological challenge later in life in chickens. Broiler and layer chicks received 2.5% DSS in drinking water during d 11 through d 18 post hatch or plain drinking water as a control. As an immunological challenge all birds received a combination of Escherichia coli lipopolysaccharide (LPS) and human serum albumin (HuSA) intramuscularly (i.m.) at d 35, and antibody titers against LPS, HuSA, and keyhole limpet hemocyanin (KLH) were determined to investigate effects of intestinal inflammation early in life on humoral immunity later in life. DSS treated birds showed a decrease in BW from which broilers quickly recovered, but which persisted for several weeks in layers. Histological examination of intestinal samples showed symptoms similar to those in rodents, including shortening and loss of villi and crypts as well as damage of the epithelial cell layer of different parts of the intestine. Effects of DSS on intestinal morphology were less severe in broilers that also showed a lower mortality in response to DSS than layers. No effect of DSS on ileal cytokine expression levels could be observed, but ileal immunoglobulin expression levels were decreased in DSS treated broilers that also showed lower antibody titers against LPS in response to the challenge. In conclusion, DSS may serve as a model for intestinal pathology early in life, although more research on the appropriate dose is necessary and is likely to differ between breeds. Results from the present study could indicate that broilers are less susceptible to DSS compared with layers or have a better capacity to recover from intestinal pathology.

Genetic and Non-Genetic Inheritance of Natural Antibodies Binding Keyhole Limpet Hemocyanin in a Purebred Layer Chicken Line

Natural antibodies (NAb) are defined as antibodies present in individuals without known antigenic challenge. Levels of NAb binding keyhole limpet hemocyanin (KLH) in chickens were earlier shown to be heritable, and to be associated with survival. Selective breeding may thus provide a strategy to improve natural disease resistance. We phenotyped 3,689 white purebred laying chickens for KLH binding NAb of different isotypes around 16 weeks of age. Heritabilities of 0.12 for the titers of total antibodies (IgT), 0.14 for IgM, 0.10 for IgA, and 0.07 for IgG were estimated. We also estimated high, positive genetic, and moderate to high, positive phenotypic correlations of IgT, IgM, IgA, and IgG, suggesting that selective breeding for NAb can be done on all antibody isotypes simultaneously. In addition, a relatively substantial non-genetic maternal environmental effect of 0.06 was detected for IgM, which may reflect a transgenerational effect. This suggests that not only the genes of the mother, but also the maternal environment affects the immune system of the offspring. Breaking strength and early eggshell whiteness of the mother's eggs were predictive for IgM levels in the offspring, and partly explained the observed maternal environmental effects. The present results confirm that NAb are heritable, however maternal effects should be taken into account.

Functional analysis of carp interferon-gamma: evolutionary conservation of classical phagocyte activation

In teleost fish two IFN-gamma gene sequences were found for which two phylogenetic clusters can be distinguished. Our previous analysis of expression of these in carp led us to hypothesize that a classical IFN-gamma function is associated with the IFN-gamma2 cluster. We investigated the evolutionary conservation of the IFN-gamma function, inducing classical activation of phagocytes, thus skewing towards a Th1-like profile of immune activation. Recombinant proteins for the carp IFN-gamma sequences of both clusters were made and we studied their effects on expression of proinflammatory mediators. Carp IFN-gamma2, in contrast to carp IFN-gamma1, was powerful in inducing a proinflammatory reaction in phagocytes: a classical synergistic response with lipopolysaccharide was observed for the induction of iNOS expression and NO release, for expression of CXCL9-11-like chemokines and the expression of proinflammatory cytokines IL-1beta, TNFalpha and the IL-12 subunits p35 and p40. In contrast, like in mammals, the CXCL8-like cytokines are LPS but not IFN-gamma sensitive. These results corroborate an evolutionary conserved nature of IFN-gamma function in lower vertebrates including classical activation of phagocytes.

Immune functions in crustaceans: lessons from flies

In recent years insects, notably Drosophila, have emerged as a popular model for studying immune responses to bacterial and fungal pathogens. Due to the availability of the complete genome sequence, genome-wide scans of immune responses have been performed using microarray analyses. These analyses have revealed the presence of two major pathways: Toll and Imd. Each pathway consists of four steps: (i) recognition through pattern recognition receptors; (ii) modulation by serine proteases; (iii) signal transduction leading to translocation of transcription factors and (iv) humoral and cellular responses. We have compared the information from insects with those currently available in crustaceans, and have identified commonalities and differences. Remarkably, in both insects and crustaceans, little is known about their anti-viral responses. Future research will have to focus on these anti-viral immune responses ultimately to control viral diseases, which are at present a major threat to culturing penaeid shrimp.