Abstract
Infectious coryza (IC), an upper respiratory tract disease affecting chickens, is caused by Avibacterium paragallinarum. The clinical manifestations of IC include nasal discharge, facial swelling, and lacrimation. This acute disease results in high morbidity and low mortality, while the course of the disease is prolonged and mortality rates are increased in cases with secondary infections. Studies regarding the immune response in infected chickens are scarce, and the local immune response is the focal point of investigation. However, a large body of work has demonstrated that severe infections can impact the systemic immune response. The objective of this study was to evaluate the systemic effects of Avibacterium paragallinarum (serovar B-1) infection on immune cells in specific pathogen-free (SPF) chickens. The current study revealed the presence of a transient circulating monocyte population endowed with high phagocytic ability and clear downregulation of major histocompatibility complex class II (MHC-II) surface expression. In human and mouse studies, this monocyte population (identified as tolerant monocytes) has been correlated with a dysfunctional immune response, increasing the risk of secondary infections and mortality. Consistent with this dysfunctional immune response, we demonstrate that B cells from infected chickens produced fewer antibodies than those from control chickens. Moreover, T cells isolated from the peripheral blood of infected chickens had a lower ability to proliferate in response to concanavalin A than those isolated from control chickens. These findings could be related to the severe clinical signs observed in complicated IC caused by the presence of secondary infections.
Highlights
Avibacterium paragallinarum (Av. paragallinarum) is a gram-negative bacterium that has been isolated worldwide and is the aetiological agent of infectious coryza (IC), a disease that contributes to significant economic losses in the poultry industry
The monocyte population increased in infectious coryza expresses low levels of MHC‐II molecules In this study, we experimentally infected specific pathogen-free (SPF) chickens with Av. paragallinarum via intrasinus instillation to establish a model of infectious coryza
Low monocyte HLA-DR expression is used as a robust marker of immunosuppression or immunoparalysis, as the presence of this population has been correlated with an increased risk of secondary infections leading to late morbidity and mortality in critically ill patients admitted for sepsis, trauma or postsurgical complications [36,37,38,39,40,41]
Summary
Avibacterium paragallinarum (Av. paragallinarum) is a gram-negative bacterium that has been isolated worldwide and is the aetiological agent of infectious coryza (IC), a disease that contributes to significant economic losses in the poultry industry. Clinical signs of IC include nasal discharge, facial swelling, and lacrimation. This disease is associated with reduced egg production, poor growth, and high morbidity [1, 2]. In cases with secondary infections, exacerbation of the clinical signs of the disease and increased mortality are observed [3,4,5,6]. The causal agent of the disease is classified by the Kume haemagglutinin serotyping scheme into nine serovars (A-1, A-2, A-3, A-4, B-1, C-1, C-2, C-3, and C-4) [7]. All serovars exhibit tropism related to the upper respiratory tract, including the involvement of nasal passages, infraorbital sinuses, and paranasal sinuses
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