Local immunity of the respiratory mucosal system in chickens and turkeys

Abstract

This review article presents fundamental mechanisms of the local mucosal immunity in selected regions of the respiratory tract in healthy birds and in some pathological conditions. The respiratory system, whose mucosa come into direct contact with microorganisms contaminating inhaled air, has some associated structures, such as Harderian gland (HG), conjunctive-associated lymphoid tissue (CALT) and paranasal glands (PG), whose participation in local mechanisms of the mucosal immunity has been corroborated by numerous scientific studies.The nasal mucosa, with structured clusters of lymphoid tissue (NALT -nasal-associated lymphoid tissue) is the first to come into contact with microorganisms which contaminate inhaled air. Lymphoid nodules, made up of B cells with frequently developed germinal centres (GC), surrounded by a coat of CD4 + cells, are the major NALT structures in chickens, whereas CD8 + cells are situated in the epithelium and in the lamina propria of the nasal cavity mucosa.Studies into respiratory system infections (e.g. Mycoplasma gallisepticum) have shown the reactivity of the tracheal mucosa to infection, despite a lack of essential lymphoid tissue.Bronchus-associated lymphoid tissue (BALT) takes part in bronchial immune processes and its structure, topography and ability to perform defensive function in birds is largely age-dependent. Mature BALT is covered by a delicate layer of epithelial cells, called follicle-associated epithelium (FAE). Germinal centres (GC), surrounded by CD4 + cells are developed in most mature BALT nodules, while CD8 + lymphocytes are dispersed among lymphoid nodules and in the epithelium, and they are rarely present in GC.Macrophages make up the first line of defence mechanisms through which the host rapidly responds to microorganisms and their products in the respiratory mucosal system. Another very important element are polymorphonuclear cells, with heterophils being the most important of them. Phagocytic cells obtained from lung lavages in birds are referred to as FARM (free avian respiratory macrophages). Their number in chickens and turkeys is estimated to be 20 times lower than that in mice and rats, which indicates a deficit in the first-line of defence in the birds' respiratory system.There are numerous B cells and antibody secreting cells (ASC) present throughout the respiratory system in birds. Their role comes down to perform antigen-specific protection by producing antibodies (IgM, IgY or IgA class) as a result of contact with pathogenic factors.

Evaluation of respiratory route as a viable portal of entry for Salmonella in poultry

“…Local immunity of the respiratory mucosal system is ensured by nonspecific defensive reactions with an arsenal of mechanical and cellular defenses, supplemented when necessary by inflammatory and immune responses. [75][76][77] There is no constitutive lymphoid tissue in the trachea. However, studies investigating infections of the respiratory system have shown reactivity of the tracheal mucosa to infections, despite a lack of essential lymphoid tissue.…”

“…Conjunctivalassociated lymphoid tissue and nasal-associated lymphoid tissue, which are at the forefront of defense, are not fully functional germinal center and plasmatic cells at 4 weeks of age. 76,79 Further, B-cell responses were not detected in the trachea until 3 weeks post-infection in layer-type chickens, which is typically more than half the lifespan of the average broiler. Having assessed the high risk of contamination of chickens through the aerosol route in hatcheries, these structures appear to have a minute role in preventing infections acquired through inhalation.…”

“…The numbers of cells producing IgG, IgA, or IgM continue to increase during the following weeks; however, it is now evident that BALT requires 6 weeks to develop fully in poultry, which approaches the age of the broilers at the end of a typical production cycle. 76,78,80 Mature BALT structures consist of lymphocyte aggregates that are covered by a distinct layer of epithelial cells known as follicle-associated epithelium, which harbors considerable numbers of lymphocytes. In 6-8 week-old birds, almost every bronchial opening was surrounded by a raised ring of lymphoid tissue and germinal centers are found in most lymphoi nodules, and occasionally plasma cells are seen under the follicle-associated epithelium.…”

The effects of subcutaneous and intraocular administration of class B ODN CpG in chicken on the expression of TLR21, IFN-γ and IL-1β

“…The Harderian gland (HG) located behind the orbit of the eye plays a role in adaptive immune response, producing numerous immunoglobins and probably presenting antigens (del Cacho et al 1992, Śmiałek et al 2011, Gurjar et al 2013. Since the intraocular route is widely used in vaccination of chicken with live-attenuated viruses and bacteria (Purswell et al 2010, Gurjar et al 2013, it is important to know if this way of administration of class B CpG ODN can elicit the proinflamatory response.…”

Three-step Anti-aMPV IgA Expression Profile Evaluation in Turkeys of Different Immunological Status after TRT Vaccination

“…Humoral immunity of the body mucous membranes is associated with IgA (also reffered to as secretory IgA -sIgA) (Snoeck et al 2006, Smialek et al 2011.…”