Oral administration of BSA-FITC-loaded polylactic acid microparticles (green) prepared via phase inversion nanoencapsulation (PIN) resulted in rapid uptake (within 15 minutes) and persistence (for at least 24 hours) in the Peyer's patches (PP) of 10 week-old APC^min/+ mice (magenta, dendritic cells; blue, B-cells). Uptake in the PP was followed by trafficking of the particles to the mesenteric lymph nodes. Particles could not be visualized in the villi or the enterocytes of the small intestine or in the colon. Oral IL-10 PIN particles ameliorated intestinal polyposis and systemic symptoms of disease in the APC^min/+ mice via neutralization of CD4⁺Foxp3⁺RORγt⁺IL-17⁺ pathogenic T-regulatory cells found in the immune structures of the gastrointestinal tract. For details, see article by Chung and colleagues on page 5377.