Innate and adaptive immune responses to Listeria monocytogenes: a short overview

Abstract

The Gram-positive facultative intracellular bacterium Listeria monocytogenes is a model pathogen for elucidating important mechanisms of the immune response. Infection of mice with a sub-lethal dose of bacteria generates highly reproducible innate and adaptive immune responses, resulting in clearance of the bacteria and resistance to subsequent L. monocytogenes infection. Both the innate and adaptive immune systems are crucial to the recognition and elimination of this pathogen from the host.

PD-1 on dendritic cells impedes innate immunity against bacterial infection

“…In addition to IL-12 and TNF-␣, we also observed significant increases of other cytokines in DKO sera, including IFN-␥ ( Figure 4C), which is probably produced by NK cells. 2 Further analysis demonstrates that NK cells, but not DCs, are the major producer of IFN-␥ after LM infection (data not shown). This implicates a cytokine cascade in LM infection involving other innate immune cells and that PD-1-mediated negative regulation is an important player in the control of infection.…”

“…2,32 Up-regulation of PD-1 by LM infection implies that expression of PD-1 may be a consequence of TLR and/or cytokine signaling. To test this, we next stimulated sDCs with various cytokines and TLR ligands in vitro to assess their ability to modulate PD-1 surface expression.…”

“…1,2 An effective innate immune response allows the host to develop antigen-specific adaptive immune responses in which T and B cells are responsible for the clearance of the infection. 3 At the cellular level, neutrophils and macrophages are thought to be the major innate cells killing LM.…”

“…3 At the cellular level, neutrophils and macrophages are thought to be the major innate cells killing LM. 2,4 In recent years, dendritic cells (DCs) have also been implicated in playing a critical role in innate immunity. 5 A subset of DCs (TipDC) have been shown to produce tumor necrosis factor-␣ (TNF-␣) and iNOS, which, contributes to bacteria inhibition.…”

The arsenal of virulence factors deployed byListeria monocytogenesto promote its cell infection cycle

“…Host survival is thus dependent on the development of an effective adaptive immune response, which, if not provided, can permit bacteria to re-enter the bloodstream and possibly reach the brain or the placenta, causing potentially fatal systemic infections. [21][22][23] Since the first isolation of Listeria, several important discoveries have been made. In the early 60s, Mackaness and colleagues showed the implication of Listeria in cellular immunity by using a mouse model of infection for L. monocytogenes.…”