Efficient scavenger receptor‐mediated uptake and cross‐presentation of negatively charged soluble antigens by dendritic cells

Abstract

SUMMARYExogenous antigens endocytosed in large amounts by antigen-presenting cells (APC) are presented on major histocompatibility complex (MHC) class I molecules as well as on class II molecules, a process called cross-presentation. Among APC, dendritic cells (DC) play a key role in cross-presentation by transporting internalized antigen to the cytosol. The present study shows that ovalbumin (OVA) introduced with negative charges by succinylation (Suc-OVA), maleylation (Mal-OVA) or cis-aconitylation (Aco-OVA) was efficiently taken up by DC via scavenger receptors (SR). Mal-OVA and Aco-OVA were efficiently cross-presented by DC, while cross-presentation of Suc-OVA was hardly observed. MHC class I presentation of acylated OVA introduced directly into the cytosol was inefficient and presentation of exogenous native OVA but not of Aco-OVA was markedly augmented by chloroquine, an inhibitor of endosomal acidification, suggesting that deacylation in endosomes or lysosomes is necessary for cross-presentation of acylated OVA. MHC class I presentation of exogenous native OVA and Aco-OVA by DC was blocked by lactacystin and brefeldin A, demonstrating that exogenous antigens taken up by DC are cross-presented through the conventional cytosolic pathway. Therefore, SR-mediated delivery of antigen to DC leads to efficient cross-presentation, although the pathway of chemical modification should be considered.

Scavenger Receptors and Resistance to Inhaled Allergens

“…In vitro assays confirmed that the absence of receptors did not affect AM binding of OVA, as doubledeficient AMs bound Alexa-OVA to nearly the same extent as did control AMs (data not shown). These findings are consistent with previous reports indicating that, unlike chemically modified albumin, native albumin binding to MΦs is not mediated through SRAs (17)(18)(19), and also indicate that nebulization does not per se denature the allergenic proteins sufficiently to create SRA-binding domains.…”

“…The context for our findings includes the recognition of the important role of dendritic cells (DC) in the pathogenesis of asthma (21), and as professional antigen-presenting cells which bridge innate and adaptive immunity (22,23). DCs express SR-AI/II, which functions in antigen presentation and adaptive immunity (17,19,(24)(25)(26)(27)(28). For example, SR-AI/II -/-mice are deficient in mounting an efficient T cell response to maleylated murine serum albumin, a known SR-AI/II ligand (29).…”

“…AMs can efficiently bind and internalize unopsonized particles and bacteria through SRAs, leading to the clearance of inhaled matter from the airways and the reduction of the resulting inflammation (7-9), and are known to similarly bind modified proteins (17)(18)(19). To determine if SRAs could reduce allergic inflammation by simply 'scavenging' aeroallergen with a resulting decrease in allergen dose, we measured their ability to internalize inhaled allergens using FITC-OVA.…”

Scavenger Receptors SR-AI/II and MARCO Limit Pulmonary Dendritic Cell Migration and Allergic Airway Inflammation

“…AMs can efficiently bind and internalize unopsonized particles and bacteria through SR-As, leading to the clearance of inhaled matter from the airways and the reduction of the resulting inflammation (7)(8)(9) and are known to similarly bind modified proteins (17)(18)(19). To determine whether SR-As could reduce allergic inflammation by simply "scavenging" aeroallergen with a resulting decrease in allergen dose, we measured their ability to internalize inhaled allergens using FITC-OVA.…”

Mannose receptor polyubiquitination regulates endosomal recruitment of p97 and cytosolic antigen translocation for cross-presentation

“…S3D), indicating that ubiquitination of the MR indeed is important for cross-presentation. In addition, the moderate cross-presentation efficiency of control cells indicates the existence of alternative pathways in these cells, which has already been observed by others (19,20). Subsequently, we investigated whether reduced cross-presentation was due to an impaired antigen transport into the cytoplasm.…”