Leishmania major activates IL-1 alpha expression in macrophages through a MyD88-dependent pathway.
Leishmania species present unusual challenges to the immune system with their capacity to downregulate inflammatory responses as well as their ability to live within macrophages. Although toll-like receptor (TLR) pathways have been implicated in the recognition of several classes of pro-inflammatory microbes, it is not known if pathogens with anti-inflammatory properties activate the host response through this family of proteins. In this study, Leishmania major stimulation of cytokine promoter-luciferase reporter constructs was examined in transfected macrophages to detect early signs of cellular activation. L. major selectively activated the promoter region of IL-1 alpha, but not IL-6, IL-8, IL-10, or an NF-kappa B reporter. IL-1 alpha mRNA expression was also stimulated by L. major, although at lower levels than lipopolysacharide-stimulated macrophages. No IL-1 alpha protein was detectable in stimulated cell lysates or culture supernatants. Transfection of macrophages with a dominant-negative version of myeloid differentiation factor 88 (MyD88), an adaptor protein which interacts with TLRs, inhibited activation of the IL-1 alpha promoter. Furthermore, stimulation of IL-1 alpha RNA expression by L. major was inhibited in peritoneal macrophages from MyD88-/- as compared to MyD88+/+ mice. These observations indicate that L. major stimulates IL-1 alpha promoter activity and mRNA expression in macrophages through MyD88-dependent pathways. However, additional anti-inflammatory pathways must also be activated which downregulate transcription and ultimately inhibit translation of the IL-1 alpha protein. Examination of promoter activation is a powerful tool for understanding the early events in macrophage activation for anti-inflammatory pathogens such as Leishmania that have mechanisms to downregulate transcription and translation.
Hawn
Thomas R
TR
Division of Infectious Diseases, Department of Medicine, University of Washington, Seattle, WA 98195, USA.
Ozinsky
Adrian
A
Underhill
David M
DM
Buckner
Frederick S
FS
Akira
Shizuo
S
Aderem
Alan
A
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D000943:Antigens, Differentiation / Q000378:metabolism*; D002460:Cell Line; D004797:Enzyme-Linked Immunosorbent Assay; D005786:Gene Expression Regulation; D017930:Genes, Reporter / Q000235:genetics; D007375:Interleukin-1 / Q000032:analysis / Q000096:biosynthesis / Q000235:genetics*; D018320:Leishmania major / Q000502:physiology*; D008070:Lipopolysaccharides / Q000494:pharmacology; D008262:Macrophage Activation / Q000187:drug effects; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism* / Q000469:parasitology; D051379:Mice; D053594:Myeloid Differentiation Factor 88; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011971:Receptors, Immunologic / Q000378:metabolism*; D015398:Signal Transduction; D014162:Transfection
D048868:Adaptor Proteins, Signal Transducing; D000943:Antigens, Differentiation; D007375:Interleukin-1; D008070:Lipopolysaccharides; C507780:Myd88 protein, mouse; D053594:Myeloid Differentiation Factor 88; D012333:RNA, Messenger; D011971:Receptors, Immunologic