Abstract
The obligate intracellular Gram-negative bacterium Chlamydia psittaci often causes avian chlamydiosis and influenza-like symptoms in humans. However, the commercial subunit C. psittaci vaccine could only provide a partial protection against avian chlamydiosis due to poor cellular immune response. In our previous study, a recombinant herpesvirus of turkeys (HVT)-delivered vaccine against C. psittaci and Marek’s disease based on human cytomegalovirus (CMV) promoter (rHVT-CMV-pmpD) was developed and provided an effective protection against C. psittaci disease with less lesions and reduced chlamydial loads. In this study, we developed another recombinant HVT vaccine expressing the N-terminal fragment of PmpD (PmpD-N) based on human elongation factor-1 alpha (EF-1α) promoter (rHVT-EF-pmpD) by modifying the HVT genome within a bacterial artificial chromosome. The related characterization of rHVT-EF-pmpD was evaluated in vitro in comparison with that of rHVT-CMV-pmpD. The expression of PmpD-N was determined by western blot. Under immunofluorescence microscopy, PmpD-N protein of both two recombinant viruses was located in the cytoplasm and on the cell surface. Growth kinetics of rHVT-EF-pmpD was comparable to that of rHVT-CMV-pmpD, and the growth rate of rHVT-EF-pmpD was apparently higher than that of rHVT-CMV-pmpD on 48, 72, and 120 h postinfection. Macrophages activated by rHVT-EF-pmpD could produce more nitric oxide and IL-6 than that activated by rHVT-CMV-pmpD. In this study, a recombinant HVT vaccine expressing PmpD-N based on EF-1α promoter was constructed successfully, and a further research in vivo was needed to analyze the vaccine efficacy.
Highlights
Chlamydia psittaci is an emerging zoonotic pathogen of global significance, which can cause avian chlamydiosis [1], and infection in human with pneumonia, encephalitis, endocarditis, and even death [2]
A recombinant herpesvirus of turkeys (HVT) expressing polymorphic membrane protein D (PmpD)-N based on cytomegalovirus (CMV) promoter was constructed to successfully elicit an exceptional cellular and humoral immunity, and proved to confer a partial protection in chickens against C. psittaci challenge infection [10]. We developed another recombinant HVT vaccine expressing PmpD-N based on elongation factor-1 alpha (EF-1α) promoter, and its morphological and immunological characterization was analyzed in comparison with rHVT-CMV-pmpD in vitro
Typical plaques appeared in the chicken embryo fibroblast (CEF) monolayers, these plaques being similar in size and morphology compared with those formed by rHVT-CMV-pmpD (Figure 1)
Summary
Chlamydia psittaci is an emerging zoonotic pathogen of global significance, which can cause avian chlamydiosis [1], and infection in human with pneumonia, encephalitis, endocarditis, and even death [2]. Recombinant HVT Vaccine against C. psittaci vaccine is available because the cellular and humoral immunity are both necessary to protect animals from this obligate intracellular bacterial infection [7]. The major outer membrane protein (MOMP) and the autotransported polymorphic membrane protein D (PmpD) of C. psittaci are proved to be good vaccine candidates [8,9,10]. PmpD has more merit than MOMP because PmpD is conserved and can elicit early immune-mediated neutralization of an ongoing chlamydial infection [11, 12]. The specific neutralizing antibody triggered by N-terminal fragment of PmpD (PmpD-N) may provide humoral immune protection against early infection [12]
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