Regulatory T cells (Tregs) are vital for maintaining a balanced immune response and their dysfunction is often
associated with auto-immune disorders. We have previously shown that antigen-loaded anionic liposomes
composed of phosphatidylcholine (PC) and phosphatidylglycerol (PG) and cholesterol can induce strong antigenspecific
Treg responses. We hypothesized that altering the rigidity of these liposomes while maintaining their
size and surface charge would affect their capability of inducing Treg responses. The rigidity of liposomes is
affected in part by the length and saturation of carbon chains of the phospholipids in the bilayer, and in part by
the presence of cholesterol. We used atomic force microscopy (AFM) to measure the rigidity of anionic OVA323-
containing liposomes composed of different types of PC and PG, with or without cholesterol, in a molar ratio of
4:1(:2) distearoyl (DS)PC:DSPG (Young's modulus (YM) 3611 ± 1271...
Show moreRegulatory T cells (Tregs) are vital for maintaining a balanced immune response and their dysfunction is often
associated with auto-immune disorders. We have previously shown that antigen-loaded anionic liposomes
composed of phosphatidylcholine (PC) and phosphatidylglycerol (PG) and cholesterol can induce strong antigenspecific
Treg responses. We hypothesized that altering the rigidity of these liposomes while maintaining their
size and surface charge would affect their capability of inducing Treg responses. The rigidity of liposomes is
affected in part by the length and saturation of carbon chains of the phospholipids in the bilayer, and in part by
the presence of cholesterol. We used atomic force microscopy (AFM) to measure the rigidity of anionic OVA323-
containing liposomes composed of different types of PC and PG, with or without cholesterol, in a molar ratio of
4:1(:2) distearoyl (DS)PC:DSPG (Young's modulus (YM) 3611 ± 1271 kPa), DSPC:DSPG:CHOL
(1498 ± 531 kPa), DSPC:dipalmitoyl (DP)PG:CHOL (1208 ± 538), DPPC:DPPG:CHOL (1195 ± 348 kPa),
DSPC:dioleoyl (DO)PG:CHOL (825 ± 307 kPa), DOPC:DOPG:CHOL (911 ± 447 kPa), and DOPC:DOPG
(494 ± 365 kPa). Next, we assessed if rigidity affects the association of liposomes to bone marrow-derived
dendritic cells (BMDCs) in vitro. Aside from DOPC:DOPG liposomes, we observed a positive correlation between
liposomal rigidity and cellular association. Finally, we show that rigidity positively correlates with Treg responses
in vitro in murine DCs and in vivo in mice. Our findings underline the suitability of AFM to measure
liposome rigidity and the importance of this parameter when designing liposomes as a vaccine delivery system.
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