Bacterial lipoproteins and other factors released by Francisella tularensis modulate human neutrophil lifespan: effects of a TLR1 SNP on apoptosis inhibition.

Abstract

F. tularensis infects several cell types including neutrophils, and aberrant neutrophil accumulation contributes to tissue destruction during tularemia. We demonstrated previously that F. tularensis strains Schu S4 and LVS markedly delay human neutrophil apoptosis and thereby prolong cell lifespan, but the bacterial factors that mediate this aspect of virulence are undefined. Herein, we demonstrate that bacterial conditioned medium (CM) can delay apoptosis in the absence of direct infection. Biochemical analyses show that CM contained F. tularensis surface factors as well as outer membrane components. Our previous studies excluded roles for LPS and capsule in apoptosis inhibition, and current studies of [14 C] acetate-labeled bacteria argue against a role for other bacterial lipids in this process. At the same time, studies of isogenic mutants indicate that TolC and virulence factors whose expression requires FevR or MglA were also dispensable, demonstrating that apoptosis inhibition does not require type I or type VI secretion. Instead, we identified bacterial lipoproteins (BLPs) as active factors in CM. Additional studies of isolated BLPs demonstrated dose-dependent neutrophil apoptosis inhibition via a TLR2-dependent mechanism that is significantly influenced by a common polymorphism, rs5743618, in human TLR1. These data provide fundamental new insight into pathogen manipulation of neutrophil lifespan and BLP function.

DOI: 10.1111/cmi.12795

Cite this paper

@article{Kinkead2017BacterialLA, title={Bacterial lipoproteins and other factors released by Francisella tularensis modulate human neutrophil lifespan: effects of a TLR1 SNP on apoptosis inhibition.}, author={Lauren C. Kinkead and Laura C Whitmore and Jenna M. McCracken and J. Raymond Fletcher and Brandi B Ketelsen and Justin Kaufman and Bradley D. Jones and David Weiss and Jason H. Barker and Lee-Ann H Allen}, journal={Cellular microbiology}, year={2017} }