Intestinal Microfold Cells Play a Critical Role in the Uptake and Oral Tolerance Mediated by Lysophosphatidylserine-Containing Lipidic Nanoparticles.

Phosphatidylserine (PS) is an anionic phospholipid that is exposed to the outer leaflet of the cell membrane during apoptosis. This PS externalization can teach the immune system to tolerate an antigen without eliciting immunological consequences. Previously, we showed that mice treated with PS nanoparticles containing single-chain PS (LysoPS) induced oral tolerance towards therapeutic proteins, whereas double-chain PS did not. These observations suggest that structural alterations of PS play a critical role in its tolerogenic potential. Given that intestinal microfold cells (M-cells) facilitate the transport of particulate antigens from the intestinal lumen to Peyer's patches (PP) for immune surveillance, we hypothesized that the failure of double-chain PS to induce tolerance may result from insufficient uptake by M-cells. The M cell-mediated uptake was investigated using in vitro and ex vivo studies and oral tolerance towards ovalbumin (OVA) was studied in M-cell-deficient mice. Consistent with this hypothesis, our data showed that LysoPS nanoparticles displayed at least a 2-fold increase in immune cell exposure and M-cell-mediated uptake compared to double-chain PS-containing nanoparticles. Importantly, LysoPS-mediated oral tolerance was absent in M cell-deficient mice with higher anti-ova antibody titers than the wild-type strain. These studies demonstrate that higher PS exposure on LysosPS nanoparticles compared to double chain could play a significant role in M cell-mediated tolerance.