DIFFERENCES IN THE IMMUNE RESPONSE OF BROILERS AND LAYERS FOLLOWING EXPERIMENTAL APEC INFECTION

In a recent study, the pathological outcomes of experimental infection with avian pathogenic Escherichia coli (APEC) in specific pathogen free (SPF) broilers and layers were investigated, demonstrating higher susceptibility in broilers compared to layer-type birds. To align these findings with immunological data, phenotypic changes in mononuclear cells of SPF broilers and layers following APEC infection were investigated. Thirty-two SPF broiler and the same number of layer chicks were divided into two groups each. At 14 days of life, one group from each bird type was infected with ilux2-tagged APEC via aerosol exposure, while the remaining groups served as controls. Following infection, birds from each group were sequentially necropsied at 3, 7, 10, and 14 days for sampling. IgG titers were measured by ELISA, and lung and spleen samples were collected to determine the frequency of mononuclear cell subsets by flow cytometry. Both infected groups demonstrated a significant rise in IgG post-infection, with antibodies being detected in infected broilers from 7 dpi onward, while the titres increased in infected layers from 10 dpi onward. In infected broilers, a significant increase of CD8α+ cells in the lung was observed. Additionally, a significant decrease in CD4+ cells in the lung and TCR-γδ+ cells as well as Bu-1+ cells in the spleen was detected. In infected layers, an increase in CD8α+ cells and a reduction of monocytes/macrophages in the lung compared to non-infected birds were observed. The findings indicate bird type specific differences in cellular and humoral immune responses following APEC infection. APEC infection caused significant changes of lymphocyte populations in the lung and spleen of broilers whereas in layers cellular variations were exclusively observable in the lung. This difference indicates that the systemic immune response is less affected compared to broilers.