IL15 and Salmonella Infections: As transgenic mice expressing LSP-IL-15 mounted a robust immune response following Salmonella infection, whereas mice expressing the non-secreted SSP-IL-15 did not, it was postulated that the over-expressed SSP-IL-15 isoform may compete with endogenous IL-15 for binding to IL-15Rα and inhibit IL-15 signaling (14).