Immunity to bacterial infection in the chicken

•Knowledge of immunity to bacterial infection in the chicken is largely based on studies of Salmonella.•Interaction with the innate immune system is important in protection and pathogenesis of Salmonella.•Salmonella infection elicits both antibody and protective cellular responses.•Regulation of the intestinal immune response is likely to be important in understanding bacterial intestinal colonization.•‘Systems’-based approaches offer improves understanding of immunity and bacterial pathogenesis. Bacterial infections remain important to the poultry industry both in terms of animal and public health, the latter due to the importance of poultry as a source of foodborne bacterial zoonoses such as Salmonella and Campylobacter. As such, much focus of research to the immune response to bacterial infection has been to Salmonella. In this review we will focus on how research on avian salmonellosis has developed our understanding of immunity to bacteria in the chicken from understanding the role of TLRs in recognition of bacterial pathogens, through the role of heterophils, macrophages and γδ lymphocytes in innate immunity and activation of adaptive responses to the role of cellular and humoral immunity in immune clearance and protection. What is known of the immune response to other bacterial infections and in particular infections that have emerged recently as major problems in poultry production including Campylobacter jejuni, Avian Pathogenic Escherichia coli, Ornithobacterium rhinotracheale and Clostridium perfringens are discussed.