Cationic stearic acid-chitosan micelles enhance intranasal antigen delivery and mucosal immunity

Chitosan (CS), as an effective mucosal adjuvant, suffers from poor solubility at neutral pH value. Inspired by the membrane-fusion and hydrophobic properties of fatty acid, stearic acid (SA) was grafted onto CS to form water-soluble, positively charged CS-SA micelles, facilitating antigen delivery. Here, the nasal adjuvant capacity of CS-SA micelles was evaluated using model antigen ovalbumin (OVA). Results showed that OVA loaded CS-SA micelles (OVA-CS-SA) exhibited a moderate positive charge (7.2 mV), high antigen loading efficiency (EE > 87 %), and good stability against pH and nasal electrolyte. Compared with free OVA, OVA-CS-SA significantly enhanced mucus permeability (P_app by 2.01-fold) and epithelial transport (P_app by 2.34-fold), improved macrophage antigen uptake (2.45-fold in RAW 264.7 cells), and upregulated antigen-presentation and costimulatory markers (MHC I/II, CD80/CD86/CD40) on dendritic cells. Intranasal immunization with OVA-CS-SA raised lung sIgA and serum IgG, promoted splenocyte proliferation (∼50 %), boosted the secretion of IL-4, IL-17, and IFN-γ, and increased the proportion of central memory T cells in the spleen. Overall, CS-SA micelles improved nasal antigen delivery and augmented mucosal and systemic immune responses in a mouse model, supporting their candidacy as an effective intranasal adjuvant.