Date of Award

5-2009

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Animal Biotechnology & Biomedical Sciences

First Advisor

Juan Anguita

Second Advisor

Barbara Osborne

Third Advisor

Alejandro P. Heuck

Subject Categories

Cell Biology

Abstract

The Lyme disease spirochete Borrelia burgdorferi is the only known human pathogen that directly activates invariant natural killer T (iNKT) cells. The number and activation kinetics of iNKT cells vary greatly among different strains of mice. Here, we report the role of the iNKT cell response in the pathogenesis of Lyme disease using C57BL/6 (B6) mice, a strain with optimal iNKT cell activation that is resistant to the development of spirochetal-induced inflammation. During experimental infection of B6 mice with B. burgdorferi , iNKT cells localize to the inflamed heart where they are activated by CD1d-expressing macrophages. Activation of iNKT cells in vivo results in the production of IFNγ, which we demonstrate controls the severity of murine Lyme carditis by at least two mechanisms. First, IFNγ greatly enhances the recognition of B. burgdorferi by macrophages, leading to increased phagocytosis of the spirochete. Secondly, IFNγ activation of macrophages increases the surface expression of CD1d, thereby facilitating further iNKT activation. Collectively, our data demonstrate that in the resistant background, B6, iNKT cells modulate acute murine Lyme carditis through the action of IFNγ, which appears to self-renew through a positive feedback loop during infection. Inflammation during infection with B. burgdorferi is dependent on the ability of the spirochete to evade local mechanisms of clearance. Even though macrophages are the main infiltrating cell during Lyme carditis, the identification of a receptor capable of mediating phagocytosis of B. burgdorferi has been elusive. Here, we demonstrate that the integrin CR3 is able to mediate binding to the spirochete and facilitate phagocytosis in a complement-dependent and independent manner. Expression of CR3, but not CR4, in CHO cells markedly enhanced their capacity to interact with B. burgdorferi , in the absence and presence of complement opsonization. Furthermore, the interaction between CR3 and B. burgdorferi is dependent on the metal-ion-dependent adhesion site (MIDAS) and could be blocked with EDTA. Inhibition of CR3 with blocking antibody was able to completely abrogate phagocytosis of B. burgdorferi by the macrophage-like RAW264.7 cells and partially block uptake by bone marrow-derived macrophages (BMMs), a finding that was recapitulated with CD11b-deficient BMMs. We further show that activation with recombinant IFNγ increases the transcription of CD11b and CD18, which correlates with increased surface expression of CR3, and that the effect of IFNγ on the phagocytosis of B. burgdorferi is circumscribed to CR3 activity, because inhibition of CR3 is able to completely diminish the effect of IFNγ on the phagocytosis of the B. burgdorferi . Lastly, our results demonstrate that CR3 is a negative regulator of proinflammatory cytokine induction in macrophages responding to B. burgdorferi . Overall, our data demonstrate roles for CR3 in the binding, phagocytosis and proinflammatory cytokine elicited by B. burgdorferi and shed light on the role of IFNγ in mediating the clearance of the spirochete during Lyme disease.

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Cell Biology Commons

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