Mechanismus der Gruppe A Streptokokken zur Umgehung der Immunabwehr bei Hautinfektion
Immunologie
Zusammenfassung der Projektergebnisse
The burden of GAS diseases is the highest in socio-economically disadvantaged communities, including the indigenous communities of Australia, where rates of skin and invasive infections, and of acute rheumatic fever (ARF) and rheumatic heart disease (RHD), are amongst the highest in the world. There is increased acceptance that recurrent skin infections, not just throat infections, are linked to ARF and RHD as well as kidney diseases. Therefore, there is a pressing need to understand the pathogenesis of GAS infection, particularly within the skin, especially since no commercial vaccine is currently available. Significant advances have been made in GAS molecular microbiology research, yet our understanding of the immune responses to GAS, particularly during the early critical phase of infection, has not kept in pace with these advances. We have selected a highly invasive isolate (NS88.2) from the Northern Territory for this work, the extreme diversity of GAS strains in this region has recently been shown to reflect globalscale transmission. Therefore, this study investigating the pathogenesis of NS88.2 is of both national and global relevance. After establishing the intravital imaging model using multi-photon and confocal microscopy we realised that the cytotoxicity of both, NS88.2 and NS88.2rep, made it impossible to acquire images for quantitative analysis. Both bacteria would lyse the cells if the concentration was too high. Only on rare occasions, in areas with very few bacteria, I was able to have neutrophils and bacteria in the same FOV. Therefore, we focused on narrowing down the pathways used by NS88.2 for immune evasion. We ruled out various pathways within the host, commonly controlling S.pyogenes infections, namely the complement system, inflammasome formation, TNF-α and IFN-γ signalling pathways. Using knockout mice and blocking these pathways, the survival of mice infected with NS88.2 was not altered. Interestingly, comparing NS88.2 with the commonly used strain 5448AP, we could demonstrate that the invasiveness of NS88.2 does not rely on the presence of the human plasminogen in contrast to 5448AP. Furthermore, NS88.2, but not 5448AP caused a systemic cytokine storm within 24-48h. This indicates that NS88.2 uses different mechanism of immune evasion compared to 5448AP, even though both harbor an inactivating mutation in the CovR/S two-component system. Another approach was the knock-out of candidate genes within the GAS genome, which are associated with invasiveness and overexpression in NS88.2 compared to NS88.2rep. The deletion of sclA, gls24, prp or ska did not alter the survival of infected mice. As preliminary data demonstrated that the majority of NS88.2 bacteria were not associated with Ly6G+ neutrophils, we wanted to further investigate this. Using a pH sensitive dye which allowed us to distinguish between phagocytosed and associated bacteria, we discovered that invasive strain NS88.2 was significantly less phagocytosed compared to NS88.2rep. This indicated that NS88.2 developed strategies to resist phagocytosis or hide from phagocytes. Comparing the overexpressed genes in NS88.2, compared to NS88.2rep, which are involved in phagocytosis and associated with increased invasiveness, we identified a new candidate gene, hasA. The gene hasA encodes the hyaluronate synthase which is required for the synthesis of the hyaluronic acid capsule of GAS. Capsular hyaluronic acid (HA) is known to resist phagocytosis and is a critical virulence factor. The knock-out of hasA alone increased the survival to 100%, comparable to the non-invasive strain NS88.2rep. Interestingly and surprisingly, the knockout did not affect phagocytosis, where neutrophils were still unable to phagocytose NS88.2ΔhasA, similar to NS88.2.
Projektbezogene Publikationen (Auswahl)
- (2018) Noncanonical Hippo Signalling in the Regulation of Leukocyte Function. Trends in immunology 39 (8) 656–669
Kurz, Angela R. M.; Catz, Sergio D.; Sperandio, Markus
(Siehe online unter https://doi.org/10.1016/j.it.2018.05.003) - (2018) The lymphoid cell network in the skin Immunol Cell Biol
Tikoo S, Rohit J, Kurz AR, Weninger W
(Siehe online unter https://doi.org/10.1111/imcb.12026) - (2018) The Yin and Yang of Tyrosine Kinase Inhibition During Experimental Polymicrobial Sepsis. Front. Immunol. 9:901
Gonçalves-de-Albuquerque CF, Rohwedder I, Silva AR, Ferreira AS, Kurz AR, Cougoule C, Klapproth S, Eggersmann T, Silva JD, Oliveira GPd, Capelozzi VL, Schlesinger GG, Costa ER, Estrela Marins RdCE, Mócsai A, Maridonneau-Parini I, Walzog B, Rocco PRM, Sperandio M and Castro-Faria-Neto HCd
(Siehe online unter https://doi.org/10.3389/fimmu.2018.00901)
