The role of phagosomal pH on the size-dependent efficiency of cross-presentation by dendritic cells

Abstract

Vaccines able to stimulate CD8+T cells are crucial in controlling a broad range of infectious diseases and tumors. To induce effective CD8+T cell responses, exogenous antigen has to be cross-presented onto major histocompatibility complex (MHC) class I molecules by dendritic cells. Although particle size has been recognized as a critical factor of vaccine design, it is unclear how the size of vaccine carriers impacts the intracellular processing of exogenous antigen and cross-presentation onto MHC class I molecules. In this study, by using polystyrene beads with narrowly defined sizes as model antigen carriers, we demonstrate that particle size mediates the efficiency of cross-presentation of exogenous antigens. By examining the intracellular trafficking, kinetics of phagosomal pH and degradation of antigens bounded to beads, we illustrate the possible mechanisms attributed to the profound effect of particle size on the efficiency of cross-presentation. Antigen bounded to 50 nm beads was shuttled rapidly to an acidic environment within half an hour post-exposure to cells, leading to its rapid and unregulated degradation and inefficient cross-presentation. In contrast, antigen bounded to 500 nm and 3 μm beads remained in a more neutral environment, which preserved the majority of antigens, leaving it available for the generation of peptides to be loaded onto MHC class I molecules. We conclude that the size of antigen carriers plays a critical role in directing antigen to the class I antigen presentation pathway. Our results, together with previous in vivo studies on the effect of particle size on CD8+T cell responses, provide insight into the rational design of vaccines for the stimulation of cell-mediated immunity.

Induction of Endoplasmic Reticulum–Endosome Fusion for Antigen Cross-Presentation Induced by Poly (γ-Glutamic Acid) Nanoparticles

“…1A, 1B). Similar results were obtained with 1-mm diameter polystyrene microbeads, which are used as a marker of phagocytosis (22). In contrast, the cell entry of the clathrin-dependent endocytosis marker transferrin (23) was not inhibited by cytochalasin D or amiloride, indicating that these reagents specifically inhibited actin-dependent phagocytosis/macropinocytosis.…”

“…The first ER-endosome fusion complex was reported with regard to phagosome entrapping of microsized latex beads (49). A recent report also suggests that the efficiency of crosspresentation is dependent on the size of the carrier (22). Therefore, optimization of the g-PGA NP size of may be useful for efficient cross-presentation to induce strong tumor immunity.…”

Novel, High Throughput Method to Study in Vitro Protein Release from Polymer Nanospheres

“…47 To this end, protein release kinetics were studied for five different chemistries of TRBSA-encapsulated CPH:SA nanospheres with the fluorescence-based protein detection assay in release media with three different buffered pH values: 7.3 (neutral), 6.0 (mildly acidic), and 4.3 (intracellular pH). 47 Because of the small sample size (∼1 mg nanospheres) and the buffering capabilities of the release medium, it is highly unlikely that the polymer degradation will alter the pH of the release buffer. The high throughput technique allowed for concurrent, rapid protein quantification of a twodimensional combinatorial library varying in nanosphere chemistry and pH of the release medium.…”

Improved antigen cross-presentation by polyethyleneimine-based nanoparticles

“…Both chloroquine and NH 4 Cl inhibit acidification of endosomes and have been reported to increase crosspresentation of exogenous antigens. [29][30][31] However, treatment with chloroquine or NH 4 Cl actually reduced PEI-OVA nanoparticle-mediated cross-presentation ( Figure 6). We think this is because the inhibition of endosome acidification by chloroquine and NH 4 Cl reduced the proton influx and prevented endosome rupture and antigen escape.…”