Processing and Major Histocompatibility Complex Class II Presentation ofLegionella pneumophilaAntigens by Infected Macrophages

Abstract

To better understand interactions between the intracellular pathogen Legionella pneumophila and macrophages (Ms), host and bacterial determinants important for presentation of antigens on major histocompatibility complex class II molecules (MHC-II) were investigated. It was determined that immune CD4 T-cell responses to murine bone marrow-derived Ms (BMs) infected with wild-type L. pneumophila were higher than the responses to avirulent dotA mutant bacteria. Although this enhanced response by immune T cells required modulation of vacuole transport mediated by the Dot/Icm system, it did not require intracellular replication of L. pneumophila. Intracellular cytokine staining identified a population of immune CD4 T cells that produced gamma interferon upon incubation with BMs infected with wild-type L. pneumophila that did not respond to M infection with dotA mutant bacteria. Endocytic processing was required for presentation of L. pneumophila antigens on MHC-II as determined by a defect in CD4 T-cell responses when the pH of BM endosomes was neutralized with chloroquine. Investigation of MHC-II presentation of antigens by BMs infected with L. pneumophila icmR, icmW, and icmS mutants indicated that these mutants have an intermediate presentation phenotype relative to those of wild-type and dotA mutant bacteria. In addition, it was found that antigens from dot and icm mutants are presented earlier than antigens from wild-type L. pneumophila. Although immune CD4 T-cell responses to proteins secreted by the L. pneumophila Lsp system were not detected, it was found that the Lsp system is important for priming L. pneumophila-specific T cells in vivo.These data indicate that optimal antigen processing and MHC-II presentation to immune CD4 T cells involves synthesis of L. pneumophila proteins in an endoplasmic reticulum-derived compartment followed by transport to lysosomes.Naive T cells expressing a unique T-cell receptor become antigen-specific effector cells upon encountering a professional antigen-presenting cell that has a cognate peptide major histocompatibility complex (MHC) displayed on its surface (2). Effector T cells play an important role in immunity to pathogens by producing factors that either upregulate cellular antimicrobial functions or that kill infected target cells that display a cognate peptide MHC (11,20). T cells producing the CD4 protein typically respond to peptides presented on MHC class II molecules (MHC-II), whereas a peptide-loaded MHC-I will stimulate T cells producing CD8. Most antigens loaded onto MHC-I are derived from proteins that have gained access to the cell cytosol, such as viral antigens or antigens released by bacterial pathogens that escape membrane-bound compartments and replicate in the cytosol of their host (21, 28). In contrast, peptides loaded onto MHC-II are derived from antigens that are transported to lysosomes, such as those produced by organisms that remain in vacuoles that undergo endocytic maturation after internalization by an antigen-presenting cell (8, 11).There are...

Role of Toll-Like Receptor 9 in Legionella pneumophila -Induced Interleukin-12 p40 Production in Bone Marrow-Derived Dendritic Cells and Macrophages from Permissive and Nonpermissive Mice

“…To ensure that chloroquine treatment was not affecting the uptake and intracellular survival of L. pneumophila, CFU were measured in the DC cultures from both mouse strains and in macrophages from A/J mice. As reported by others (5,33,45), macrophages from A/J mice supported the replication of L. pneumophila, as evidenced by an increase in the number of CFU (Fig. 2D); however, intracellular growth was not seen in DCs from both mouse strains, and furthermore, chloroquine treatment had no effect on the number of CFU (Fig.…”

“…TLR9 is activated by DNA or synthetic oligonucleotides, such as murine ODN1826, that contain unmethylated CpG (21), and the activity of these receptors can be blocked by inhibitory ligands, such as murine ODN2088 (41), or by treatment with the antimalarial chloroquine, which through its buffering capacity interferes with acidification or maturation of the endosomes (39,46). Chloroquine has been reported to suppress the antigenpresenting function of L. pneumophila-infected macrophages due to neutralization of endocytic compartments (8,17,33). Regarding dendritic cells (DCs), L. pneumophila is internalized by these cells, similar to case for macrophages, but the bacterium does not grow intracellularly (34).…”

IL-1R signaling enables bystander cells to overcome bacterial blockade of host protein synthesis

“…All strains harbored the pSS128 plasmid encoding an M45-tagged β-lactamase-RalF fusion protein (22). For in vitro and in vivo studies, L. pneumophila was cultured on charcoal yeast extract agar containing 6.25 μg/mL chloramphenicol for 48 h at 37°C before infection (19,(49)(50)(51).…”

Macrophage activation by polysaccharide biological response modifier isolated from Aloe vera L. var. chinensis (Haw.) Berg.

“…Activated macrophage can act as accessory cells/antigen presenting cells (APCs) and sources of cytokines for the activation of other immune effector cells [6,7]. As APCs, antigens are engulfed by phagocytosis or endocytosis, and internalized antigens are digested into fragments and antigen peptides are finally associated with MHC class II molecule on the cell surface for antigen presentation [8]. The major cytokines produced by macrophages for the modulation of other immune cells are proinflammatory cytokines: IL-1, IL-6 and TNF-α [9,10].…”