title: Toll-like receptor 2 deficiency results in impaired antibody responses and septic shock during Borrelia hermsii infection.
abstract: Overwhelming bacteremia is a leading cause of death. To understand the mechanisms involved in protective antibody and pathological inflammatory responses during bacteremia, we have been studying the murine model of Borrelia hermsii infection. Toll-like receptor (TLR) signaling plays an important role in generating the rapid anti-B. hermsii antibody responses required for the resolution of bacteremia. Using NF-κB reporter assays, we found that B. hermsii activates TLR2 and TLR9. However, TLR2(-/-) TLR9(-/-) mice exhibited an impairment in anti-B. hermsii antibody responses similar to that of TLR2(-/-) mice. Moreover, the impairment in the antibody responses of TLR2(-/-) mice or TLR2(-/-) TLR9(-/-) mice coincides with an order-of-magnitude-higher bacteremia, and death results from septic shock, as evidenced by a dysregulated systemic cytokine response and characteristic organ pathology. Since TLR2 appears to be the major extracellular sensor stimulated by B. hermsii, we hypothesized that during elevated bacteremia the activation of intracellular sensors of bacteria triggers dysregulated inflammation in TLR2(-/-) mice. Indeed, blocking the internalization of B. hermsii prevented the induction of inflammatory cytokine responses in TLR2-deficient cells. Furthermore, we found that B. hermsii activates the cytoplasmic sensor nucleotide-binding oligomerization domain 2 (NOD2). Macrophages deficient in both TLR2 and NOD2 have impaired cytokine responses to B. hermsii compared to cells lacking TLR2 alone, and B. hermsii-infected TLR2(-/-) NOD2(-/-) mice exhibited improved survival compared to TLR2(-/-) mice. These data demonstrate that TLR2 is critical for protective immunity and suggest that, during heightened bacteremia, recognition of bacterial components by intracellular sensors can lead to pathological inflammatory responses.
authors.affiliation: Department of Microbiology and Immunology, Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, PA 19107, USA.
authors.forename: Gregory S
authors.initials: GS
authors.lastname: Dickinson
authors.forename: Heather
authors.initials: H
authors.lastname: Piccone
authors.forename: Guizhi
authors.initials: G
authors.lastname: Sun
authors.forename: Egil
authors.initials: E
authors.lastname: Lien
authors.forename: Louis
authors.initials: L
authors.lastname: Gatto
authors.forename: Kishore R
authors.initials: KR
authors.lastname: Alugupalli
mesh_terms: D000818:Animals; D000907:Antibodies, Bacterial / Q000097:blood; D000917:Antibody Formation / Q000276:immunology*; D016470:Bacteremia / Q000276:immunology / Q000382:microbiology / Q000473:pathology; D001898:Borrelia / Q000145:classification / Q000276:immunology / Q000472:pathogenicity*; D002460:Cell Line; D004195:Disease Models, Animal; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D053473:Nod2 Signaling Adaptor Protein / Q000235:genetics / Q000378:metabolism; D012061:Relapsing Fever / Q000276:immunology* / Q000382:microbiology / Q000473:pathology; D012772:Shock, Septic / Q000276:immunology* / Q000382:microbiology; D015398:Signal Transduction; D051195:Toll-Like Receptor 2 / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism
chemical_list: D000907:Antibodies, Bacterial; D053473:Nod2 Signaling Adaptor Protein; C495945:Nod2 protein, mouse; C493486:Tlr2 protein, mouse; D051195:Toll-Like Receptor 2