Pathogenicity and immunogenicity of Listeria monocytogenes small-plaque mutants defective for intracellular growth and cell-to-cell spread

Abstract

Listeria monocytogenes strains previously generated by transposon mutagenesis were examined with respect to virulence and induction of protective immunity in BALB/c mice. The phenotypic defects observed in these mutant L. monocytogenes strains included decreased hemolysin (listeriolysin 0 [LLO]) production, phospholipase C activity, intracellular growth, and/or cell-to-cell spread in vitro. While 50%o lethal dose determinations performed with these mutant strains indicated reduced virulence for BALB/c mice, sublethal infection with the * Corresponding author.

Delivery of a viral antigen to the class I processing and presentation pathway by Listeria monocytogenes.

“…Like killed L. monocytogenes, LLO-negatire mutants fail to enter the cytoplasm and induce protective immunity (8,11). Although both LLO-positive and -negative L. monocytogenes target the class II pathway in infected macrophages, only macrophages infected by LLO-positire bacteria are targeted for lysis by CD8 + T cells (8,9). These results are consistent with a requirement of bacterial entry into the cytoplasm to induce CD8 + T cells.…”

“…The immune response to L. monocytogenes is considered a paradigm of T cell-mediated immunity, as both the CD4 + and CD8 + T cell subsets contribute to the resolution of infection, whereas antibody plays no measurable role (2). Adoptive transfer studies have implicated CD8 + cells as the most critical effector T cell subset (5,6) that secretes cytokines (7,8) and actively lyses infected cells in vitro (9,10). The induction of protective immunity to L. monocytogenes requires administration of live hemolytic bacteria (11,12).…”

Protective Immunity to Listeria Monocytogenes Infection Mediated by Recombinant Listeria innocua Harboring the VGC Locus

“…Since Lm is located in both phagosomes and cytosol of professional antigen-presenting cells during infection, epitopes derived from Listeria proteins are presented by the MHC pathway thereby priming both effector CD4 + and CD8 + T cells [28,29] resulting in full elimination of Listeria from the host. Previous experimental studies [30,31] have revealed that persistence and number of viable microorganisms are important parameters for establishing efficient T cell-mediated immunity. Moreover, it has been shown that the presence of live bacteria in mice organs over the first 48 hours after immunization is critical for the induction of effector CD8 + T cell mechanisms [32].…”

Assessing Vacuolar Escape of Listeria Monocytogenes

“…However, how these bacterial virulence factors specifically contribute to Listeria vacuolar escape is not fully understood. For example, inactivation of LLO in J774 cells completely abrogates bacterial translocation to the cytoplasm [14,17] but in human epithelial HeLa, HEp-2 and Henle 407 cells, the broad range phospholipase PlcB can rescue a Δhly mutant, suggesting that host factors also contribute to the stability of the bacterial vacuole. Indeed, it has been demonstrated in murine macrophages that the gamma-interferon-inducible lysosomal thiol reductase (GILT) and the cystic fibrosis transmembrane conductance regulator (CFTR) enhance the oligomerization and the lytic activity of LLO to facilitate vacuolar rupture [18,19] while inducible renitence limits vacuolar disruption by restoring the integrity of endolysosomal membranes [20].…”