Abstract
Bacterial glycoproteins have been investigated as vaccine candidates as well as diagnostic biomarkers. However, they are poorly understood in Mycobacterium bovis strain bacille Calmette-Guérin (BCG), a non-pathogenic model of Mycobacterium tuberculosis. To understand the roles of secreted O-mannosylated glycoproteins in BCG, we conducted a ConA lectin-affinity chromatography and mass spectra analysis to identify O-mannosylated proteins in BCG culture filtrate. Subsequent screening of antigens was performed using polyclonal antibodies obtained from a BCG-immunized mouse, with 15 endogenous O-mannosylated proteins eventually identified. Of these, BCG_0470 and BCG_0980 (PstS3) were revealed as the immunodominant antigens. To examine the protective effects of the antigens, recombinant antigens proteins were first expressed in Mycobacterium smegmatis and Escherichia coli, with the purified proteins then used to boost BCG primed-mice. Overall, the treated mice showed a greater delayed-type hypersensitivity response in vivo, as well as stronger Th1 responses, including higher level of IFN-γ, TNF-α, and specific-IgG. Therefore, mannosylated proteins BCG_0470 and BCG_0980 effectively amplified the immune responses induced by BCG in mice. Together, our results suggest that the oligosaccharide chains containing mannose are the antigenic determinants of glycoproteins, providing key insight for future vaccine optimization and design.
Highlights
Tuberculosis (TB), caused by Mycobacterium tuberculosis (M. tuberculosis), remains a major threat to public health, with ever increasing morbidity and mortality rate worldwide (WHO, 2019)
bacille Calmette-Guérin (BCG), an attenuated Mycobacterium bovis strain developed as a vaccine by Calmette and Guérin in 1921, is the only licensed TB vaccine approved by the World Health Organization
Protein O-mannosylation process occurs in both eukaryotes and prokaryotes, including the important human pathogen M. tuberculosis, the etiological agent of TB (Espitia and Mancilla, 1989)
Summary
Tuberculosis (TB), caused by Mycobacterium tuberculosis (M. tuberculosis), remains a major threat to public health, with ever increasing morbidity and mortality rate worldwide (WHO, 2019). Current TB health interventions include treatment of latent TB infection and childhood immunization using the bacille Calmette-Guérin (BCG) vaccine (Martinez et al, 2017; WHO, 2019). Latent TB infection prevention services are often not accessible to eligible patients, BCG vaccination coverage generally achieves a rate of at least 90% (WHO, 2019). BCG, an attenuated Mycobacterium bovis strain developed as a vaccine by Calmette and Guérin in 1921, is the only licensed TB vaccine approved by the World Health Organization. Its efficacy is varied, nearly 100 years of BCG use confirms that this living bacilli alone inducessubstantial immune protection against TB (Pym et al, 2003; Nieuwenhuizen and Kaufmann, 2018). Identifying and characterizing the most immunogenic and efficient antigens in the BCG vaccine may help to completely eliminate TB infection
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