Pierre Voet

Inhibition of Borrelia burgdorferi-Tick Interactions In Vivo by Outer Surface Protein A Antibody

Borrelia burgdorferi outer surface protein (Osp) A is preferentially expressed by spirochetes in the Ixodes scapularis gut and facilitates pathogen-vector adherence in vitro. Here we examined B. burgdorferi-tick interactions in vivo by using Abs directed against OspA from each of the three major B. burgdorferi sensu lato genospecies: B. burgdorferi sensu stricto, Borrelia afzelii, and Borrelia garinii. Abs directed against B. burgdorferi sensu stricto (isolate N40) destroy the spirochete and can protect mice from infection. In contrast, antisera raised against OspA from B. afzelii (isolate ACA-1) and B. garinii (isolate ZQ-1) bind to B. burgdorferi N40 but are not borreliacidal against the N40 isolate. Our present studies assess whether these selected OspA Abs interfere with B. burgdorferi-tick attachment in a murine model of Lyme disease with I. scapularis. We examined engorged ticks that had fed on B. burgdorferi N40-infected scid mice previously treated with OspA (N40, ACA-1, ZQ-1, or mAb C3.78) or control Abs. OspA-N40 antisera or mAb C3.78 destroyed B. burgdorferi N40 within the engorged ticks. In contrast, treatment of mice with OspA-ACA-1 and OspA-ZQ-1 antisera did not kill B. burgdorferi N40 within the ticks but did effectively interfere with B. burgdorferi-I. scapularis adherence, thereby preventing efficient colonization of the vector. These studies show that nonborreliacidal OspA Abs can inhibit B. burgdorferi attachment to the tick gut, highlighting the importance of OspA in spirochete-arthropod interactions in vivo.

Function of Neisserial Outer Membrane Phospholipase A in Autolysis and Assessment of Its Vaccine Potential

ABSTRACT Outer membrane phospholipase A (OMPLA) is an outer membrane-localized enzyme, present in many gram-negative bacterial species. It is implicated in the virulence of several pathogens. Here, we investigated the presence, function, and vaccine potential of OMPLA in the human pathogen Neisseria meningitidis. Immunoblot analysis showed the presence of OMPLA in 28 out of 33 meningococcal strains investigated. The OMPLA-negative strains all contained a pldA gene, but these alleles contained premature stop codons. All six Neisseria gonorrhoeae strains tested, but only two out of seven commensal neisserial strains investigated, expressed OMPLA, showing that OMPLA is expressed by, but not limited to, many pathogenic neisserial strains. The function of OMPLA was investigated by assessing the phenotypes of isogenic strains, expressing no OMPLA, expressing wild-type levels of OMPLA, or overexpressing OMPLA. OMPLA exhibited phospholipase activity against endogenous phospholipids. Furthermore, OMPLA was characterized as an autolysin that acted under specific conditions, such as prolonged growth of the bacteria. The vaccine potential of the protein was investigated by immunizing mice with in vitro refolded, recombinant OMPLA. High levels of antibody titers were obtained, but the murine sera were neither bactericidal nor protective. Also, convalescent patients and vaccinee sera did not contain detectable levels of anti-OMPLA antibodies, indicating that OMPLA may not be sufficiently immunogenic to be included in a meningococcal vaccine.

Vaccination of natural reservoir hosts with recombinant lipidated OspA induces a transmission-blocking immunity against Lyme disease spirochaetes associated with high levels of LA-2 equivalent antibodies

As observed in humans, immune responses in naturally infected reservoir hosts of Borrelia burgdorferi sensu lato rarely target the outer surface proteins (Osp) A and B of Lyme disease spirochaetes. The absence of protective immunity in such hosts following tick-borne infection allows them to play an effective role in the maintenance of Lyme borreliosis in nature. Therefore, the question was addressed whether one of the most prominent natural reservoir host species of B. burgdorferi s.l. in Europe, the yellow-necked mouse (Apodemus flavicollis), may lack the ability to elicit transmission-blocking antibodies to Lyme borreliosis spirochaetes. Yellow-necked mice were immunized with a recombinant lipidated OspA from B. burgdorferi sensu stricto or with high numbers of UV-irradiated whole spirochaetes. All immunized mice, but not untreated controls, developed polyclonal humoral immune responses to OspA (31 kDa). Serum antibodies of animals vaccinated with the recombinant OspA contained high levels of antibody to an epitope of OspA, defined by the monoclonal antibody LA-2, whereas only low levels of LA-2 equivalent antibodies could be detected in sera from animals immunized with killed spirochaetes. Ixodes ricinus ticks infected with B. burgdorferi s.s. lost their spirochaete load after feeding on animals with high levels of LA-2 equivalent antibody; ticks feeding on animals which had only low or undetectable serum levels of LA-2 equivalent antibodies retained their spirochaete infection. Furthermore, animals with high levels of LA-2 equivalent antibody were protected against spirochaete infection. Our study shows that natural mouse reservoir hosts are highly competent to generate transmission-blocking antibodies after vaccination with a lipidated recombinant OspA and indicates that antibodies to the LA-2 epitope play a key role in the destruction of B. burgdorferi s.s. within feeding Ixodes ricinus ticks.

Animal models for meningococcal disease.

There are many in vitro systems for the study of meningococcal pathogenesis, but it is only in animal models of infection that the interactions of the bacteria with whole tissues and the humoral and cellular immune systems can be assessed. Animal-infection models are also of great importance for the assessment of the protective efficacy of existing and candidate vaccines. However, the relevance of these animal models to human disease and how well protection assessed in them corresponds to protection against human disease, must always be considered. Animal models for pathogenic Neisseria have been previously reviewed (1).