Complement sensitivity and factor H binding of European Francisella tularensis ssp. holarctica strains in selected animal species

Abstract

Francisella tularensis is a Gram%negative bacterium, the causative agent of the 19 zoonotic disease tularaemia. The bacterium has deve loped several extracellular and 20 intracellular strategies to evade the hosts’ innate and adaptive immune responses. The aims of 21 the study were to examine complement sensitivity of wild and attenuated F. tularensis ssp. 22 holarctica strains in animal hosts of distinct sensitivity to the bacterium, to compare the 23 complement evading ability of wild strains of diffe rent phylogeographic background, and to 24 examine the role of factor H in the host%pathogen i nteractions. Complement sensitivity assays 25 were carried out on various F. tularensis ssp. holarctica wild strains and on the attenuated 26 live vaccine strain (LVS) with the sera of the high ly sensitive house mouse ( Mus musculus ), 27 moderately sensitive European brown hare ( Lepus europaeus ) and the relatively resistant 28 cattle ( Bos taurus ). Specific binding of complement regulator factor H to bacterial membrane 29 proteins was examined by Western blot assays. All w ild strains interacted with the hosts’ 30 complement system and showed no significant differe nces in their survivability. The 31 attenuated LVS was resistant to serum killing in mo use, but was lysed in the sera of hare and 32 cattle. Direct binding of factor H to F. tularensis membrane proteins was not detected