Page 386 - Avian Virology: Current Research and Future Trends

Avian Immune Responses to Virus Infection

Lonneke Vervelde * and Jim Kaufman * 14
1
2

1 The Roslin Institute and The Royal (Dick) School of Veterinary Science, University of Edinburgh, Easter Bush, Midlothian, UK.
2 University of Cambridge, Department of Pathology, and Department of Veterinary Medicine, Cambridge, UK.
*Correspondence: lonneke.vervelde@roslin.ed.ac.uk and jfk31@cam.ac.uk
https://doi.org/10.21775/9781912530106.14

Abstract A major function of an immune response is to recognize and
All organisms have evolved a large number of complicated and eliminate invading micro-organisms. The immune system of
interwoven immune responses to defend themselves against a vertebrates is made up of two functional elements, the innate
wide variety of pathogens. The vast majority of what is known and adaptive, which differ in their mechanism of pathogen rec-
about immunity is from research on humans and biomedical ognition and time of response. Traditionally innate responses
model species. However, the challenges faced by the poultry were viewed as rapid responses upon invasion of pathogens,
industry because of infectious diseases from viruses has driven defined by phagocytosis and lytic functions. The innate immune
research over many decades. Innate immunity consists of many system is now considered to be the first line of defence using
different systems dependent on a wide variety of host genes, germline-encoded receptors and includes a major role in immu-
provides the initial stages of response against all pathogens, nomodulation and induction of adaptive immune responses. The
can provide protection in individuals with the appropriate host later adaptive responses, cellular and humoral, use highly specific
alleles, and is crucial for initiation and guidance of the adaptive T- and B-lymphocytes with antigen receptors that are generated
immune system. Adaptive immunity is particularly important as by gene rearrangement.
the basis for vaccination, in which innate immunity is stimulated The immune response to virus infections has been far better
by adjuvants present in the vaccines. However, the genetics of characterized in mammals compared with chickens. This chapter
adaptive immunity can also be important, as resistance to many describes our current general understanding of the avian innate
economically important viruses is dependent on particular and adaptive responses to virus and is focused on the differ-
generalist alleles of the molecules encoded by the major histocom- ences and anomalies compared with the mammalian response.
patibility complex (MHC). Further research should elucidate the The reader will be referred to previously published reviews on
molecular bases for both innate and adaptive immune responses, mammalian responses with regard to general features of immune
allowing better genetic breeding, improved vaccines and applica- responses to virus infections if unknown in or similar to the
tion to birds outside of the poultry industry. chicken. The other chapters in this book will describe the immune
responses to specific viruses in more depth, whereas this chapter
will describe the general concepts.
Introduction
Despite advances made in the diagnosis of and vaccination for
viral diseases in poultry, viruses are the major cause of negative Innate host responses
impact to the poultry industry by infecting birds worldwide. Mucosal surfaces, in particular the respiratory tract, are the
Highly pathogenic avian influenza, low pathogenic avian influ- main site of entry and uptake of the avian viruses which have a
enza, Newcastle disease and infectious bronchitis are the four major impact on the industry; avian influenza virus (AIV), infec-
most important diseases in terms of the number of livestock tious bronchitis virus (IBV), Newcastle disease virus (NDV),
units lost for poultry species (World Bank, 2011). The treatment Marek’s disease virus (MDV), infectious laryngotracheitis virus
and prevention of viral infections are of utmost importance for (ILTV), and avian metapneumovirus (aMPV). Airway defence
the industry, not only because they have a devastating effect on mechanisms are highly efficient in both the clearance of viruses
poultry flocks, but they can also render flocks immunosuppressed and prevention of clinical consequences and the intracellular
and susceptible to opportunistic infections. It is vital to develop nature of viruses has led to a rigorous selection and adaptation
new control strategies, such as antivirals, vaccines and breeding of both the virus and host. Viruses are selected on their ability
strategies, and with this in mind a greater understanding of the to evade the immune system, to enable replication and spread to
chicken’s immune response to viruses will also assist with the other hosts. Elimination of the host will reduce the availability of
design of novel strategies. susceptible hosts and will not benefit the virus. Highly adapted