Vesicle architecture licenses antigen-specific memory T cell immunity after mucosal immunization with infection-derived vesicles.

Small extracellular vesicles (sEVs) released by infected cells carry microbial antigens together with host immunomodulatory molecules, yet whether their structural integrity governs the durability of protective immunity is unknown. Using Salmonella infection as a model, we show that sEVs isolated from infected macrophages act as potent antigen carriers for intranasal immunization. In BALB/c mice, intact sEVs elicited antigen-specific serum IgG responses comparable in magnitude to those induced by live attenuated Δ aroA Salmonella. Immunization further increased fecal IgA binding to Salmonella following lethal challenge and generated serum capable of enhancing macrophage-mediated bacterial uptake. Single-cell RNA sequencing of mesenteric lymph nodes revealed enrichment of mature B cells, effector CD8 T cells, and central memory-like CD4 T cells expressing CD69, CD44, CCR7, and Sell/CD62L, while defined recombinant sEV-associated antigens drove IFN-γ and IL-2 production by memory T cells ex vivo. Disrupting vesicle architecture by sonication left total IgG and IgG1 induction intact but selectively impaired IgG2a responses and antigen-specific T-cell recall; intact sEVs, by contrast, drove greater dendritic-cell CD80 expression, IL-2 production by cocultured CD69+ CD4 T cells, and prolonged survival after lethal challenge. These findings establish that vesicle integrity is dispensable for the overall magnitude of antibody induction but is required to instruct dendritic-cell costimulation, Th1-associated IgG2a class switching, and durable memory T-cell recall after mucosal immunization, identifying infection-derived sEVs as structurally organized immunogens rather than passive antigen reservoirs.