Abstract
Avibacterium paragallinarum, the causative agent of infectious coryza, is known to release outer membrane vesicles (OMVs). In the present study, we investigated the composition, bioactivities, and functional properties of the OMVs of A. paragallinarum. Following extraction and purification, the OMVs were observed to be spherical in shape, with diameters ranging from 20 to 300 nm. The vesicles contained endotoxin as well as genomic DNA. The molecular weights of the OMV-contained protein fragments were mostly concentrated at 65 and 15 kDa. The components of the OMV proteins were mainly various functional enzymes (e.g., ATP-dependent RNA helicase), structural components (e.g., streptomycin B receptor and membrane protein), and some hypothetical proteins with unknown functions. The expression levels of inflammation-related factors, such as interleukin (IL)-2, IL-6, IL-1β, IL-10, and inducible nitric oxide synthase (iNOs), were significantly upregulated in chicken macrophage cells HD11 incubated with OMVs. Serum IgG antibodies were measured after two intramuscular injections of an OMV-based vaccine into specific pathogen-free (SPF) chickens. The vaccinated chickens were then challenged by A. paragallinarum of homologous and heterologous serovars. It was noted that the vaccinated chickens produced immunoglobulin G (IgG) antibodies against A. paragallinarum. The OMVs conferred an acceptable level of protection (70%), defined as an absence of colonization and of clinical signs, against the homologous strain (serovar A), while the cross-protection against heterologous challenge with serovars B and C was much weaker. However, the OMVS did provide significant protection against clinical signs for all three serovars. Overall, this study laid a foundation for further unraveling the functional roles of OMVs released by A. paragallinarum.
Highlights
Infectious coryza is an acute respiratory disease of poultry that causes significant economic losses by inducing growth retardation and impairing egg production
The outer membrane vesicles (OMVs) were found to be both closely associated with bacterial cells as well as distinctly separated from the cells of A. paragallinarum
At 24 h, compared to the control group, the expression levels of IL-1β, IL-10, and inducible nitric oxide synthase were remarkably higher (p < 0.01) in the cells exposed to OMV and LPS, while the Detection of Nucleic Acids in OMVs
Summary
Infectious coryza is an acute respiratory disease of poultry that causes significant economic losses by inducing growth retardation and impairing egg production. The continuing problem of outbreaks of infectious coryza, including in North America (Crispo et al, 2018) and Europe (Heuvelink et al, 2018), highlights the importance of unraveling the interaction between A. paragallinarum and the host immune response. The release of outer membrane vesicles (OMVs) by Gramnegative bacteria has been observed and extensively studied over the past decades (Jan, 2017), including Haemophilus influenzae (Deich and Hoyer, 1982; Roier et al, 2016) and A. paragallinarum (Ramon Rocha et al, 2006) in the family Pasteurellaceae. OMVs are ubiquitously produced both in vitro and in vivo during an infection (Roier et al, 2016) and play a crucial role in host-microbe interactions (Turnbull et al, 2016). Little is known about the immunogenic potential of OMVs derived from A. paragallinarum
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