NLRP3 inflammasome-activating arginine-based liposomes promote antigen presentations in dendritic cells.
The NLRP3 inflammasome activation has been proposed as a common mechanism for some adjuvants to boost the immune system, and cationic liposomes were reported to potentially activate the NLRP3 inflammasome. Herein, we questioned whether the NLRP3 inflammasome-activating cationic liposomes could promote antigen presentation and be applied as an immune adjuvant. In addition, we aimed to investigate the structure effect of lipid on triggering these immune responses. A series of structurally similar lipids, consisting of arginine (Arg) head group and varied lengths of alkyl chains or spacers in between were used to prepare cationic liposomes. Lipopolysaccharide-primed human or murine macrophages or phorbol 12-myristate 13-acetate-primed THP-1 cells were treated with these liposomes, and interleukin (IL)-1β secretion was measured to quantify the NLRP3 inflammasome activation. Lysosome rupture was examined in THP-1 cells by the fluorescence loss of acridine orange, a lysosome dye. Further, chicken ovalbumin (OVA) was loaded on the liposome surface and applied to murine bone marrow-derived dendritic cells (BMDCs), which activate OT-I and OT-II lymphocytes upon major histocompatibility complex (MHC) class I- and class II-mediated antigen presentation, respectively. OT-I and OT-II cell division and IL-2 secretion were measured to evaluate the antigen presentation efficiency. The expressions of MHC molecules and co-stimulatory molecules ie, CD80, CD86, and CD40 on BMDCs were investigated by flow cytometry. All the liposomes showed size distributions of 80-200 nm and zeta potentials of around 50 mV. A3C14 liposomes, consisting of Arg-C3-Glu2C14 lipids induced the most potent lysosome rupture and NLRP3 inflammasome activation. OVA-A3C14 also exhibited the most potent MHC class I- and class II-mediated antigen presentation in BMDCs without interfering MHC and co-stimulatory molecules. The hydrophobic moieties of arginine-based liposomes are crucial in stimulating innate immune cells. A3C14 liposomes were non-immunogenic but strongly activated innate immune cells and promoted antigen presentation, and therefore can be applied as immune adjuvants.