Proteome Analysis and Serological Characterization of Surface-Exposed Proteins of <i>Rickettsia heilongjiangensis</i>

<div><p>Background</p><p><i>Rickettsia heilongjiangensis</i>, the agent of Far-Eastern spotted fever (FESF), is an obligate intracellular bacterium. The surface-exposed proteins (SEPs) of rickettsiae are involved in rickettsial adherence to and invasion of host cells, intracellular bacterial growth, and/or interaction with immune cells. They are also potential molecular candidates for the development of diagnostic reagents and vaccines against rickettsiosis.</p><p>Methods</p><p><i>R. heilongjiangensis</i> SEPs were identified by biotin-streptavidin affinity purification and 2D electrophoreses coupled with ESI-MS/MS. Recombinant SEPs were probed with various sera to analyze their serological characteristics using a protein microarray and an enzyme-linked immune sorbent assay (ELISA).</p><p>Results</p><p>Twenty-five SEPs were identified, most of which were predicted to reside on the surface of <i>R. heilongjiangensis</i> cells. Bioinformatics analysis suggests that these proteins could be involved in bacterial pathogenesis. Eleven of the 25 SEPs were recognized as major seroreactive antigens by sera from <i>R. heilongjiangensis</i>-infected mice and FESF patients. Among the major seroreactive SEPs, microarray assays and/or ELISAs revealed that GroEL, OmpA-2, OmpB-3, PrsA, RplY, RpsB, SurA and YbgF had modest sensitivity and specificity for recognizing <i>R. heilongjiangensis</i> infection and/or spotted fever.</p><p>Conclusions</p><p>Many of the SEPs identified herein have potentially important roles in <i>R. heilongjiangensis</i> pathogenicity. Some of them have potential as serodiagnostic antigens or as subunit vaccine antigens against the disease.</p>