Serological characterization of surface-exposed proteins of Coxiella burnetii

Abstract

The obligate intracellular Gram-negative bacterium Coxiella burnetii causes Q fever, a worldwide zoonosis. Here we labelled Cox. burnetii with biotin and used biotin-streptavidin affinity chromatography to isolate surface-exposed proteins (SEPs). Using two-dimensional electrophoresis combined with mass spectrometry, we identified 37 proteins through bioinformatics analysis. Thirty SEPs expressed in Escherichia coli (recombinant SEPs, rSEPs) were used to generate microarrays, which were probed with sera from mice experimentally infected with Cox. burnetii or sera from Q fever patients. Thirteen rSEPs were recognized as seroreactive, and the majority reacted with at least 50 % of the sera from mice infected with Cox. burnetii but not with sera from mice infected with Rickettsia rickettsii, R. heilongjiangensis, or R. typhi. Further, 13 proteins that reacted with sera from patients with Q fever did not react with sera from patients with brucellosis or mycoplasma pneumonia. Our results suggest that these seroreactive SEPs have potential as serodiagnostic antigens or as subunit vaccine antigens against Q fever.

Coxiella burnetii immunogenic proteins as a basis for new Q fever diagnostic and vaccine development

“…The 58 identified immunoreactive proteins were used for calculating the ratios of proteins exclusively found in human, mouse or the both sera. Approximately half (48%) of the total proteins found are recognized by human and mouse sera, particularly 66% in the publication of Xiong et al (2012), 44% in Wang et al (2013) and 41% in Jiao et al (2014). These common antigens represent very promising immune targets for sensitive Q fever detection in various hosts, including humans and ruminants.…”

“…A more precise conclusion about the portion of host species-specific anti-C. burnetii antigen responses can be drawn from those three publications, which analyzed human and mouse sera in parallel using the same techniques (Xiong et al, 2012a;Wang et al, 2013;Jiao et al, 2014;Ref. 16-18, Table 1).…”

“…Only one periplasmatic protein (1%) and one secreted protein (1%) were noted in the selected publications. Also, Jiao et al (2014) who analyzed protein fractions enriched for surfaceexposed antigens have revealed various cytoplasmic bacterial proteins. Subsequently, they concluded that besides technical reasons the identified cytoplasmic proteins might reside on the surface of C. burnetii and contribute to bacterium-host interactions.…”

“…Interestingly, a unique procedure based on immunocapturing of antigens on biofunctionalized magnetic microspheres using polyclonal antibodies was presented by Flores-Ramirez et al (2016). In most of these articles total protein extracts were analyzed, but few studied bacterial protein fractions enriched for outer membrane proteins (Papadioti et al, 2011;Jiao et al, 2014). These outer membrane proteins were found to be advantageous for the development of new vaccines due to their exposition to host immune cells (Hotta et al, 2004;Papadioti et al, 2011).…”

“…Localization of identified C. burnetii antigens based on annotations in the respective publication The functions of 43% of all identified proteins are stated in the publications as either known or predicted by defined algorithms, such as PSORTb 3.0.2 or SOSUI-GramN Jiao et al, 2014;Flores-Ramirez et al, 2016). The remaining 57% are classified as proteins with unknown localization, or it was not stated.…”