Refine
Document Type
- Doctoral Thesis (2)
Language
- English (2)
Has Fulltext
- yes (2)
Is part of the Bibliography
- no (2)
Keywords
- Lipoprotein (2) (remove)
Staphylococcus aureus is present in around a third of the human population as a constant commensal in the anterior nares, in a third as an intermittent commensal, and a third are non-carriers. However, S. aureus is also a dangerous pathogen, responsible for many types of infections. Recently, the emerging of methicillin-resistant S. aureus strains has aggravated the health problem. Treating infections caused by the invasive strains has become ineffective with conventional antibiotics. Noticeably, transmission of S. aureus has occurred not only in healthcare settings but also in the community; furthermore, transmission between humans and domestic animals has been reported. Although studies about host-pathogen interactions of S. aureus have advanced our knowledge in the last decades, we still have not fully understood mechanisms of the immune system in responses to S. aureus. The aim of this study is to unravel interactions of the human adaptive immune system to selected S. aureus virulence factors. In particular, the study focuses on two aspects: the reaction of human antibodies to the bacterial extracellular proteins in S. aureus-induced furunculosis with an emphasis on Panton-Valentine Leukocidin and responses of the adaptive immune system to membrane-bound lipoproteins of S. aureus. Furunculosis is a variety of hair follicle infection in which S. aureus is one of the chief causal pathogens involved. The corresponding bacterial strains are generally capable of producing of a pore-forming toxin, known as Panton-Valentine Leukocidin (PVL). Recently, the emerging of pvl-positive methicillin-resistant S. aureus has become a problem for treating the bacterially caused furuncles. Colonization with the bacteria is a risk factor for development of chronic or recurrent boils. It is not yet known why furunculosis patients are largely infants or young adults. In this context, we untangled the responses of antibody IgG antibodies to S. aureus extra-cellular factors, notably the PVL toxin, in families in which the patients were children. Multiplex PCR demonstrated that S. aureus clones, isolated from the patients’ wounds but also from the nares of family members, harbored genes coding for PVL toxin. Spa-typing highlighted that bacterial genotypes were very similar in each family. This suggests that transmission of pvl-positive S. aureus took place between family members. The finding also raises the question why only the young patients but not family members who were colonized by the same S. aureus clones suffered from furunculosis. 2D immune proteomics procedures showed a tendency of higher IgG titers against bacterial virulence factors in family healthy members than in patients. PVL-specific antibodies were measured using ELISA, in which patients’ PVL-specific IgG titers were low. This supports the idea that antibodies, probably in conjunction with T cells, might contribute to clinical protection in furunculosis. This research will serve as a foundation for future studies, in which our results should be validated in a larger cohort. Among S. aureus’ virulence factors are lipoproteins, which are anchored in the bacterial cell membrane. Lipoproteins perform various functions in colonization, immune evasion, and immunomodulation. These proteins are potent activators of the complex of innate immune receptors termed Toll-like receptors (TLR) 2 and 6. This study addressed the specific B-cell and T-cell responses to lipoproteins in human S. aureus carriers and non-carriers. 2D immune proteomics and ELISA approaches revealed that titers of serum antibody (IgG) binding to the S. aureus lipoproteins were very low or even unmeasurable in healthy individuals except for the lipoprotein SaeP. Only patients with cystic fibrosis or epidermolysis bullosa who were heavily exposed to the bacteria, generated an antibody response also to lipoproteins. Proliferation assays and cytokine profiling data showed only subtle responses of T cells in healthy individuals; three out of eight tested lipoproteins did not elicit proliferation. Hence, the robust activation of the innate immune system by S. aureus lipoproteins does not translate into a strong adaptive immune response. Reasons for this may be inaccessibility of lipoproteins for B cells as well as ineffective processing and presentation of the antigens to T cells. The main findings implicate that family members can serve as S. aureus reservoirs causing recurrent furunculosis in young patients and that antibodies may provide partial protection from such infections by S. aureus. We have found that, different from proteins that are secreted by S. aureus, lipoproteins which anchored in the bacterial cell membrane, do not trigger strong responses from the human adaptive immune system. This suggests that these proteins remain mostly hidden in the bacterial cell-wall.
Immunogenicity and protectivity of surface-localized lipoproteins of Streptococcus pneumoniae
(2019)
Steptococcus pneumoniae (pneumococcus) represents a common colonizer of the human upper respiratory tract (URT). However, under certain conditions, for example following viral infections, or in indiciduals with a weakened immune system, including young children, elderly and immunocompromised persons, it can cause a wide range of life-threatening diseases, such as pneumonia, meningitis or sepsis. Based on the polysaccharide capsule that surrounds the bacterium, pneumococci are classified into so far 98 different serotypes. Prevention of S. pneumoniae infections was achieved by the development of pneumococcal polysaccharide-based (PPSV) vaccines. However, these vaccines have important limitations, including high manufacturing costs and restricted serotype coverage facilitating replacement by non-vaccine serotypes. Aiming for the development of a serotype-independent vaccine, the potential of surface-exposed and highly conserved pneumococcal lipoproteins was evaluated for being targeted as a future protein-based vaccine. Therefore, selected lipoproteins were examined i) for their surface abundance and accessibility, ii) for their presence in clinically relevant S. pneumoniae strains, and iii) for their immunogenicity. Finally, based on these initial screenings, the most promising candidates were selected to analyze their protective efficacy in a moude model of colonization. DacB and PnrA were identified as highly abundant lipoproteins on the pneumococcal surface. They showed to be immunogenic both during natural infection using convalescent patient sera and when given to mice as a subunit vaccine formulation. Following intranasal immunization and challenge of mice with two heterologous S. pneumoniae strains, both proteins reduced the pneumococcal load in the nasopharynx. The protection correlated with increased production of IL-17A indicative for a Th17-mediated immunity, which is strongly suggested to play a critical role in preventing pneumococcal colonization and infection. Lipoproteins are triggering innate receptors on antigen-presenting cells, thereby linking innate with adaptive immune responses. Therefore, lipidated proteins were evaluated for their potential to be used as an adjuvant for vaccination. Lipidation clearly enhanced humoral immune responses to DacB and PnrA without the need of an additional adjuvant. However, an additional adjuvant was required to confer protection against pneumococcal colonization. In conclusion, Lipoproteins are interesting candidates for future protein-based vaccine strategies because they are highly conserved, abundant and immunogenic. PnrA and DacB were identified as potential candidates, since they induced protection against pneumococcal colonization, which in turn may lead to a decline in infections and transmission.