title: The detection of protective antigen (PA) associated with spores of Bacillus anthracis and the effects of anti-PA antibodies on spore germination and macrophage interactions.
abstract: The protective antigen (PA) component of the anthrax toxins is an essential virulence factor of Bacillus anthracis and is the major protective immunogen. The kinetics of PA production during growth of B. anthracis, and the roles of anti-PA antibody in host immunity are not clearly defined. Production of PA by the vegetative organisms peaks during the shift from exponential to stationary phase of growth. Recently, PA was also found to be associated with spores. In our study, PA-specific mRNA was detected in spores by RT-PCR within 15-min of exposure to germinant. PA protein was detected by immunomagnetic electrochemiluminescence (ECL) on spores within 1 h of exposure to a germination medium and was rapidly released into the supernatant. PA was not demonstrated on ungerminated spores by RNA analysis, ECL, or spore-based anti-PA ELISA; however, it was detected on ungerminated spores by immunoelectron microscopy (immunoem). In rabbits, PA induces polyclonal antibodies (Abs) that, in addition to their anti-toxin neutralizing activities, exhibit anti-spore activities. In this study, the anti-spore effects of a human monoclonal Ab specific for PA (AVP-hPA mAb, Avanir Pharmaceuticals) were characterized. AVP-hPA mAb retarded germination in vitro, and enhanced the phagocytic and sporicidal activities of macrophages. The activities were comparable to those of the polyclonal rabbit anti-rPA Ab. Assays to detect germination inhibitory activity (GIA) in serum from vaccinated mice and guinea pigs suggested a possible role for anti-PA Abs in protection. Thus, anti-PA Ab-mediated, anti-spore activities may play a role in protection during the early stages of an anthrax infection.
authors.affiliation: United States Army Medical Research Institute of Infectious Disease (USAMRIID), Bacteriology Division, 1425 Porter Street, Fort Detrick, Frederick, MD 21702, USA.
authors.forename: C K
authors.initials: CK
authors.lastname: Cote
authors.forename: C A
authors.initials: CA
authors.lastname: Rossi
authors.forename: A S
authors.initials: AS
authors.lastname: Kang
authors.forename: P R
authors.initials: PR
authors.lastname: Morrow
authors.forename: J S
authors.initials: JS
authors.lastname: Lee
authors.forename: S L
authors.initials: SL
authors.lastname: Welkos
mesh_terms: D000818:Animals; D022122:Anthrax Vaccines / Q000276:immunology; D000907:Antibodies, Bacterial / Q000276:immunology*; D000911:Antibodies, Monoclonal; D000942:Antigens, Bacterial / Q000032:analysis* / Q000276:immunology*; D001408:Bacillus anthracis / Q000737:chemistry / Q000276:immunology* / Q000502:physiology; D001427:Bacterial Toxins / Q000032:analysis* / Q000276:immunology*; D006168:Guinea Pigs; D006801:Humans; D007106:Immune Sera; D008163:Luminescent Measurements; D008264:Macrophages / Q000276:immunology* / Q000382:microbiology*; D051379:Mice; D016253:Microscopy, Immunoelectron; D010587:Phagocytosis; D012329:RNA, Bacterial / Q000032:analysis; D012333:RNA, Messenger / Q000032:analysis; D011817:Rabbits; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013171:Spores, Bacterial / Q000737:chemistry* / Q000276:immunology / Q000502:physiology; D014611:Vaccination
chemical_list: D022122:Anthrax Vaccines; D000907:Antibodies, Bacterial; D000911:Antibodies, Monoclonal; D000942:Antigens, Bacterial; D001427:Bacterial Toxins; D007106:Immune Sera; D012329:RNA, Bacterial; D012333:RNA, Messenger; C030325:anthrax toxin