The Chicken MHC: Insights into Genetic Resistance, Immunity, and Inflammation Following Infectious Bronchitis Virus Infections

Abstract

The chicken immune system has provided an immense contribution to basic immunology knowledge by establishing major landmarks and discoveries that defined concepts widely used today. One of many special features on chickens is the presence of a compact and simple major histocompatibility complex (MHC). Despite its simplicity, the chicken MHC maintains the essential counterpart genes of the mammalian MHC, allowing for a strong association to be detected between the MHC and resistance or susceptibility to infectious diseases. This association has been widely studied for several poultry infectious diseases, including infectious bronchitis. In addition to the MHC and its linked genes, other non-MHC loci may play a role in the mechanisms underlying such resistance. It has been reported that innate immune responses, such as macrophage function and inflammation, might be some of the factors driving resistance or susceptibility, consequently influencing the disease outcome in an individual or a population. Information about innate immunity and genetic resistance can be helpful in developing effective preventative measures for diseases such as infectious bronchitis, to which a systemic antibody response is often not associated with disease protection. In this review, we summarize the importance of the chicken MHC in poultry disease resistance, particularly to infectious bronchitis virus (IBV) infections and the role played by innate immunity and inflammation on disease outcome. We highlight how future studies focusing on the MHC and non-MHC genes can potentially bring clarity to observed resistance in some chicken B haplotype lines.

Keywords: IBV; chicken MHC; genetic resistance; inflammation; innate immunity.

Figure 1

Schematic representation of an antigen presenting cell internalizing pathogens in the process of phagocytosis and subsequent antigen presentation through major histocompatibility complex (MHC) molecules (A). In humans, there are six MHC class I molecules occurring in three heterozygous loci (B). In chickens, there are two MHC class I molecules occurring in one heterozygous locus (C), which allows for stronger associations with disease resistance than the human MHC class I. Adapted from Kaufman, 2013 [19].

Figure 2

Schematic representation of the chicken microchromosome 16, indicating the MHC B and Rfp-Y loci. The B locus contains the B-F/B-L and the B-G regions corresponding to MHC class I, II, III, and IV (B-G) genes. The Rfp-Y locus contains nonclassical MHC class I and II genes. Adapted from Delany et al. (2009) [61] and Kaufman (2013) [19].