Poster Presentation The Australasian Society for Immunology 2017 Annual Scientific Meeting

Distinct characteristics of the RP105-agonistic mycobacterial 19 kDa lipoprotein and RP105-mediated macrophage activation (#365)

Thomas E Schultz 1 , Chien-Hsiung Yu 1 , Karl-Heinz Wiesmüller 2 , Megan Lucas 3 , Karen M Dobos 3 , Alan G Baxter 4 , Alexandre S Cristino 5 , Antje Blumenthal 1
  1. The University of Queensland Diamantina Institute, Translational Research Institute, Brisbane, Queensland, Australia
  2. EMC microcollections GmbH, Tübingen, Germany
  3. Department of Microbiology, Immunology and Pathology, College of Veterinary Medicine, Colorado State University, Fort Collins, Colorado, USA
  4. Comparative Genomics Centre, James Cook University, Townsville, QLD, Australia
  5. The University of Queensland Diamantina Institute, The University of Queensland, Brisbane, QLD, Australia

Radioprotective 105 kDa (RP105/CD180) is a Toll-like receptor (TLR) family member that contributes to host control of mycobacterial infection. RP105 and TLR2 physically and functionally interact in recognition of mature Mycobacterium tuberculosis lipoproteins. The M. tuberculosis 19kDa lipoprotein, a well-known TLR2/TLR1 agonist, was identified to also activate host cells in an RP105-dependent manner.  The roles of TLR2 and its co-receptors, TLR1 and TLR6, in recognition of lipoproteins as well as the transcriptional signature induced downstream of TLR activation are well studied. In contrast, requirements for RP105 agonism in mycobacterial lipoproteins are unknown and the contributions of RP105 to host cell activation are poorly defined.  We thus investigated two facets of RP105-dependent macrophage activation by lipoproteins: (i) the structural basis of the RP105-dependent host cell activation by the M. tuberculosis 19 kDa lipoprotein; and (ii) RP105-mediated transcriptional events induced by this lipoprotein. Systematic analysis of various synthetic lipopeptide structures revealed that, in contrast to TLR1 and TLR6, RP105 did not discriminate between lipopeptides with two or three acyl chains. In contrast, replacement of polar residues with non-polar residues within the peptide moiety partially ablated RP105-dependent IL-6 and TNF production. This suggests that engagement of RP105 by the M. tuberculosis 19 kDa lipoprotein is dependent on protein moiety composition.  This sets RP105 agonism apart from the current TLR2/1 and TLR2/6 paradigm of lipoprotein recognition, which is determined by lipoprotein acylation status. Genome-wide gene expression analyses of M. tuberculosis 19 kDa lipoprotein-stimulated macrophages identified 107 RP105-regulated transcripts that differed from TLR-regulated transcripts. Systems biology and bioinformatics approaches identified putative transcription factors and microRNAs as upstream regulators of this gene signature. Our data indicate that RP105 activation plays a non-redundant role in the innate immune recognition of M. tuberculosis, underpinning its functions in shaping the host response to pathogenic mycobacteria.