An ITAM-signaling pathway controls cross-presentation of particulate but not soluble antigens in dendritic cells

Abstract

Dendritic cells (DC) possess a unique capacity for presenting exogenous antigen on major histocompatibility class I, a process that is referred to as cross-presentation, which serves a critical role in microbial and tumor immunity. During cross-presentation, antigens derived from pathogen-infected or tumor cells are internalized and processed by DCs for presentation to cytotoxic T lymphocytes (CTLs). We demonstrate that a signaling pathway initiated by the immunoreceptor tyrosine–based activation motif (ITAM)–containing adaptors DAP12 and FcRγ utilizes the Vav family of Rho guanine nucleotide exchange factors (GEFs) for processing and cross-presentation of particulate, but not soluble, antigens by DCs. Notably, this novel pathway is crucial for processing and presentation of particulate antigens, such as those associated with Listeria monocytogenes bacteria, yet it is not required for antigen uptake. Mechanistically, we provide evidence that in DCs, Vav GEFs are essential to link ITAM-dependent receptors with the activation of the NOX2 complex and production of reactive oxygen species (ROS), which regulate phagosomal pH and processing of particulate antigens for cross-presentation. Importantly, we show that genetic disruption of the DAP12/FcRγ–Vav pathway leads to antigen presentation defects that are more profound than in DCs lacking NOX2, suggesting that ITAM signaling also controls cross-presentation in a ROS-independent manner.

Protective T cell immunity in mice following protein-TLR7/8 agonist-conjugate immunization requires aggregation, type I IFN, and multiple DC subsets

“…First, aggregation of the protein as a consequence of conjugation with the TLR7/8 agonist by chemical treatment or UV activation leads to increased uptake of antigen by DCs and is required for T cell priming in vivo. The ability of aggregated or particulate antigens to enhance cellular immunity and specifically increase the efficiency of cross-presentation has been demonstrated with a variety of antigens and formulations (61)(62)(63). Moreover, in focusing on CD8 + T cell immunity, aggregated and particulate protein improves antigen access to cytoplasmic proteasomes, resulting in more efficient cross-presentation (13,14).…”

Phagosome maturation in polarized macrophages

“…In line with this, the maintenance of less-acidic pH values in the phagosomes of dendritic cells has been shown to promote antigen presentation by preventing excessive degradation [74 -77, 131]. As discussed in previous sections, the regulation of luminal pH is partially dependent on the activity of the NADPH oxidase, and the absence of NADPH oxidase activity at the phagosome in gp91phox-deficient, Rab27a-deficient ashen, as well as Vav-null mice, results in a more acidic phagosomal pH and as a consequence, significantly reduced antigen-presenting efficiency [74,75,132]. In addition to regulating protease activity through pH, the NADPH oxidase has been proposed to control intraphagosomal proteolysis through a redox-mediated mechanism, in which proteases, such as cysteine cathepsins, that have a cysteine in the active site are subject to reversible inhibition by ROS [78,[133][134][135].…”

NADPH Oxidase Promotes Neutrophil Extracellular Trap Formation in Pulmonary Aspergillosis

“…Among CGD patients, the degree of impairment of NADPH oxidase in neutrophils correlates with mortality (3). NADPH oxidase is rapidly activated by conditions that, in nature, are associated with infectious threat, such as the ligation of specific pathogen recognition receptors by microbial products (e.g., formylated peptides and fungal cell wall beta-glucans), opsonized particles, and integrin-dependent adhesion (4)(5)(6). Activation of the phagocyte NADPH oxidase (NOX2) requires translocation of cytoplasmic subunits p47 phox , p67 phox , and p40 phox and Rac to a membrane-bound heterodimer cytochrome comprised of gp91 phox and p22 phox .…”