Toll-like Receptor (TLR) 2 Mediates Inflammatory Responses to Oligomerized RrgA Pneumococcal Pilus Type 1 Protein

Alan Basset,Fan Zhang,Cyril Benes,Sabina Sayeed,Muriel Herd,Claudette Thompson,Douglas T Golenbock,Andrew Camilli,Richard Malley

doi:10.1074/jbc.m112.398875

Abstract

The pneumococcal type 1 pilus is an inflammatory and adherence-promoting structure associated with increased virulence in mouse models. We show that RrgA, an ancillary pilus subunit devoid of a lipidation motif, particularly when presented as part of an oligomer, is a TLR2 agonist. The surface-exposed domain III, and in particular a 49-amino acid sequence (P3), of the protein is responsible for the TLR2 activity of RrgA. A pneumococcal mutant carrying RrgA with a deletion of the P3 region was significantly reduced in its ability to activate TLR2 and induce TNF-α responses after mouse intraperitoneal infection, whereas no such difference could be noted when TLR2(-/-) mice were challenged, further implicating this region in recognition by TLR2. Thus, we conclude that the type 1 pneumococcal pilus can activate cells via TLR2, and the ancillary pilus subunit RrgA is a key component of this activation.

Highlights

The pneumococcal pilus is associated with increased inflammation
We conclude that the type 1 pneumococcal pilus can activate cells via TLR2, and the ancillary pilus subunit RrgA is a key component of this activation
We further demonstrate that a 49-amino acid region (P3) of the domain III (DomIII)3 of RrgA is necessary and sufficient for this activation

Summary

Background

The pneumococcal pilus is associated with increased inflammation. Results: A 49-amino acid region of the pilus protein RrgA activates TLR2 and is associated with increased inflammation and virulence. Available pneumococcal vaccines generate potent systemic immunity via the generation of opsonophagocytic antibodies to the capsular polysaccharide [2, 3] These vaccines, have limitations, including selective coverage of capsular types included in the vaccines, only partial protection against mucosal disease, the phenomenon of serotype replacement, and high cost (4 – 6). Complicating the picture further, our group and others recently showed that pilus expression is bistable among a clonal population [25, 26], such that only roughly 30% of cells derived from one clone express the pilus at any one time This regulation appears to be negatively regulated by RrgA [25] and positively regulated by the RlrA-positive feedback loop [27].

Part 3 of Domain III of rrgA

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION