Streptococcal pathogens express surface proteins that target inhibitory LILR and complement regulating factors
File(s)
Author(s)
Lewis Marffy, Alexander
Type
Thesis
Abstract
Background: Streptococcus pyogenes, Streptococcus agalactiae, and Streptococcus pneumonia are major causes of invasive human diseases. Bacteria must evade host immune responses to promote virulence utilising mechanisms such as targeting host inhibitory immune receptors and complement regulators. Whilst inhibitory leukocyte Ig-like receptors (LILR) are known targets of bacteria, the bacterial ligands are unknown. Similarly, streptococcal pathogens are known to target the complement regulator factor H (FH), but the mechanism of immune evasion remains unclear. Thus, the hypothesis proposed was that streptococcal pathogens target inhibitory LILR and FH to enhance bacterial immune evasion.
Method: A combination of biochemical and cellular assays using isogenic mutants were used to identify streptococcal ligands that interact with LILR. A panel of recombinant proteins and bacterial mutants were constructed to identify bacterial ligand binding domains in LILR and FH. Finally, ex vivo whole blood and neutrophil assays were performed to assess the functional consequences of the bacterial engagement with LILR and FH.
Results: This study identified the first bacterial ligands that bind inhibitory LILR: S. pyogenes M3 protein binds LILRB2 and S. agalactiae β protein binds LILRB3. Data also suggest that S. pneumoniae bind LILRB3 via a subset of PspC proteins. Two LILRB3 binding domains were identified in β protein – B75KN and B6C – and a FH binding domain in a loop in B75KN. The data suggest that β protein inhibits neutrophil phagocytosis through engagement with LILRB3, but not by sequestering FH. In contrast, M3 engagement of LILRB2 does not enhance immune evasion; however, recombinant LILRB2 inhibited M3-mediated S. pyogenes adhesion to host cells...
Method: A combination of biochemical and cellular assays using isogenic mutants were used to identify streptococcal ligands that interact with LILR. A panel of recombinant proteins and bacterial mutants were constructed to identify bacterial ligand binding domains in LILR and FH. Finally, ex vivo whole blood and neutrophil assays were performed to assess the functional consequences of the bacterial engagement with LILR and FH.
Results: This study identified the first bacterial ligands that bind inhibitory LILR: S. pyogenes M3 protein binds LILRB2 and S. agalactiae β protein binds LILRB3. Data also suggest that S. pneumoniae bind LILRB3 via a subset of PspC proteins. Two LILRB3 binding domains were identified in β protein – B75KN and B6C – and a FH binding domain in a loop in B75KN. The data suggest that β protein inhibits neutrophil phagocytosis through engagement with LILRB3, but not by sequestering FH. In contrast, M3 engagement of LILRB2 does not enhance immune evasion; however, recombinant LILRB2 inhibited M3-mediated S. pyogenes adhesion to host cells...
Version
Open Access
Date Issued
2023-09-12
Date Awarded
2024-04-01
Copyright Statement
Attribution-NonCommercial 4.0 International Licence (CC BY-NC)
License URL
Advisor
McCarthy, Alex
Sriskandan, Shiranee
Sponsor
Biotechnology and Biological Sciences Research Council/United Kingdom
NIAID NIH HHS/United States
The Royal Society
Wellcome Trust
Grant Number
BB/V006495/1/BB
R21 AI155828
RGS\R1\201044
225315/Z/22/Z
Publisher Department
Department of Infectious Disease
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)