Endogenous IL-15 might be responsible for early protection by natural killer cells against infection with an avirulent strain of Salmonella choleraesuis in mice

Interleukin (IL)-15 is a novel cytokine with growth factor activity for T c ells, B cells, and natural killer cells (NK cells). We investigated the rol e of IL-15 in the host defense against infection with avirulent Salmonella choleraesuis strain 31N-1 cured of 50-kb, virulent plasmid, IL-15 was abund antly expressed at transcription and protein levels in macrophages infected with S. choleraesuis 31N-1, The number of NK cells in the infected sites w as increased during the course of infection coincident with IL-15 productio n. Anti-IL-15 mAb, administration inhibited the emergence of NIC cells and interferon-gamma (IFN-gamma) production in serum after infection with S, ch oleraesuis 31N-1 and concurrently impaired the clearance of the bacteria. T hese results suggested that IL-15 might be responsible for protection again st avirulent S, choleraesuis infection at early stage of infection through activation of NK cells in the infected sites.