ALITALON TUTKIMUS VIELÄ KERRAN

[Bb]

Lähettäjä: Soijuv Lähetetty: 21.12.2004 12:25

Alitalon tutkimuksessa esitetään niitä mekanismeja joilla Bb tunkeutuu elimistöön ja selviytyy siellä :


http://ethesis.helsinki.fi/julkaisut/la ... mpleme.pdf

?In Lyme disease pathogenesis the ability of the spirochete to invade tissues is essential.

This ability is achieved by

1. utilization of human matrix metalloproteases (MMP?s) (68, 69),

and

2. plasmin/plasminogen (70-74).

By binding these enzymes onto its outer membrane, B. burgdorferi can penetrate through connective tissue similarly to leukocytes when they penetrate through blood vasculature. In the pathogenesis of arthritis, the use of MMPs is central to the observed damage in the synovium (75).


?We observed a form of biofilm-formation of large Borrelia burgdorferi bundles, which likely served to protect Borrelia bacteria from complement. This may be analogous to attack of the complement system on tumors, where the outer cell-layers are attacked, but the inner layers protected (128).

This mechanism has also been documented elsewhere (76). MMPs (68, 75, 129) enable the spirochetes to invade tissues and when they are able to grow into a larger population, they may be able to shield each other by forming a form of biofilm. Because there was a very large amount of bacteria, the majority of the cells were not attacked. In a physiological sense this may partially explain the difficulty in treating persistent long-term infections.

???The temporally controlled expression of virulence factors may also explain the virulence of B. garinii strains in infecting the CNS. It was observed that B. garinii strains have a higher sensitivity to complement in vitro compared to B. burgdorferi s. s. and B. afzelii strains. Nevertheless, they seem to enter the CNS where they can escape complement, which is relatively scarce inside the CNS. This may require the temporally regulated expression of virulence factors, such as OspE or Bba68-proteins or other FH-binding proteins preceding entry. As observed in study V, the OspE proteins are expressed in B. garinii strains freshly isolated from the CNS.

...9.14 Key mechanisms of pathogenesis and future studies

This work has answered some of the most central questions in Lyme isease pathogenesis. Apparently, the utilization of the FH-binding proteins, which include the OspE, and Bba68 families of proteins are important to the virulence of Borrelia burgdorferi spirochetes. A rigorous proof for this necessitates animal model studies. The generation of e.g. OspE-transfected strains of B. garinii and other analogous gene-manipulated Borreliae will be instrumental for studies of this kind.

At least two proteins (130, 131) have been studied as vaccine candidates against Lyme disease. A vaccine using OspA as antigen was sold for some time in North America, but it was withdrawn because of arthritogenic sideeffects (132). Subsequently, the vaccine was redesigned to contain a recombinant antigen lacking a potentially cross-reactive site (58 ) and currently exists as a second-generation rOspA vaccine (133). However, similarly to the first-generation OspA vaccine, the rOspA vaccine is only effective against North-American strains. In the Åland islands, Finland, a polyvalent vaccine (134), utilizing the OspC antigen (135) was undergoing clinical testing but this testing has been discontinued. Therefore, no currently available vaccine exists for the European market.

Computer prediction studies indicate that OspE has an overall coiled-coil-type structure. In this regard, it resembles other FH-binding proteins, e.g. M-protein of group A streptococci (136) and PspC-family proteins of pneumococci (41).

Future studies regarding the three-dimensional structure of OspE and Bba68- family proteins would be of potential interest for docking analysis of the FHOspE interaction, which would enable the design of targeted antigen design for vaccines and/or pharmacotherapy.

10 Conclusions

This work has demonstrated that Lyme disease spirochetes utilize FH binding as a complement evasion mechanism. The complement inhibitor factor H binds with its C terminus to plasmid-encoded OspE surface proteins of B. burgdorferi. The OspE-family of FH-binding proteins, therefore, constitutes a family of virulence factors, which affect the complement sensitivity of B. burgdorferi s. l. spirochetes. In addition, another FH-binding protein family was observed and identified by others as the Bba68-family of proteins. This information may enable the development of new, effective vaccines against a