Role of IL-12-independent and IL-12-dependent pathways in regulating generation of the IFN-gamma component of T cell responses to Salmonella typhimurium.
Clearance of facultative intracellular pathogens such as Salmonella requires IFN-gamma from CD4 T cells. Mechanisms linking intracellular pathogen recognition with induction of IFN-gamma-producing T cells are still poorly understood. We show in this study that IL-12 is not required for commitment to the IFN-gamma-producing T cell response in infection with Salmonella typhimurium, but is needed for its maintenance. The IL-12-independent signals required for commitment depend on events during the first hour of infection and are related to Ag presentation. Even transient attenuation of Ag presentation early during infection specifically abrogates the IFN-gamma component of the resulting CD4 T cell response. The IL-12 needed for maintenance is also better induced by live rather than dead bacteria in vivo, and this difference is due to specific suppression of IL-12 induction by dead bacteria. Presence of exogenous IL-4 down-modulates IL-12 production by macrophages activated in vitro. Furthermore, macrophages from IL-4-null mice secrete high levels of both IL-12 and IL-18 in response to stimulation in vivo even with dead bacteria, but this does not lead to induction of IFN-gamma-secreting T cells in response to immunization with dead S. typhimurium. Early IL-4 is contributed by triggering of CD4 NK T cells by dead, but not live, bacteria. Thus, Ag presentation-related IL-12-independent events and IL-4-sensitive IL-12-dependent events play crucial complementary roles in the generation of the IFN-gamma-committed CD4 T cell component of the immune response in Salmonella infection.
National Institute of Immunology, New Delhi, India.
Beena
B
John
Deepa
D
Rajagopal
Achal
A
Pashine
Satyajit
S
Rath
Anna
A
George
Vineeta
V
Bal
D000818:Animals; D017951:Antigen Presentation / Q000187:drug effects; D002478:Cells, Cultured; D002738:Chloroquine / Q000008:administration & dosage; D015395:Histocompatibility Antigens Class I / Q000502:physiology; D007274:Injections, Intraperitoneal; D007371:Interferon-gamma / Q000096:biosynthesis*; D018664:Interleukin-12 / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D020382:Interleukin-18 / Q000096:biosynthesis; D015847:Interleukin-4 / Q000172:deficiency / Q000235:genetics / Q000494:pharmacology; D007694:Killer Cells, Natural / Q000276:immunology; D017737:Macrophages, Peritoneal / Q000276:immunology / Q000378:metabolism / Q000382:microbiology; D051379:Mice; D018345:Mice, Knockout; D011994:Recombinant Proteins / Q000494:pharmacology; D012481:Salmonella Infections, Animal / Q000235:genetics / Q000276:immunology; D022562:Salmonella Vaccines / Q000008:administration & dosage / Q000276:immunology; D012486:Salmonella typhimurium / Q000187:drug effects / Q000254:growth & development / Q000276:immunology*; D015398:Signal Transduction / Q000276:immunology*; D016176:T-Lymphocyte Subsets / Q000187:drug effects / Q000276:immunology* / Q000382:microbiology*; D014613:Vaccines, Attenuated / Q000008:administration & dosage / Q000276:immunology
D015395:Histocompatibility Antigens Class I; D020382:Interleukin-18; D011994:Recombinant Proteins; D022562:Salmonella Vaccines; D014613:Vaccines, Attenuated; D018664:Interleukin-12; D015847:Interleukin-4; D007371:Interferon-gamma; D002738:Chloroquine