title: IL-10 fails to inhibit the production of IL-18 in response to inflammatory stimuli.
abstract: IL-10 is an inhibitor of the production of pro-inflammatory cytokines such as IL-12 and IL-1beta, but it is not known whether it can inhibit the production of IL-18. Therefore, a variety of in vivo and in vitro models were used to determine whether IL-10 is an inhibitor of IL-18 production. Infection of IL-10-/- mice with Toxoplasma gondii results in increased levels of IL-12 in the serum and in recall responses compared to wild type (WT) mice. Surprisingly, although infection resulted in increased levels of IL-18 in serum, there were no differences between WT and IL-10-/- mice. Moreover, splenocytes from infected WT and IL-10-/- mice produced similar levels of IL-18 and addition of exogenous IL-10 did not inhibit their production of IL-18. To address whether endogenous IL-18 inhibitors were masking increased IL-18 production in the IL-10-/- mice, expression of IL-18 binding protein was examined using RT-PCR. Although infection leads to increased expression of IL-18BP mRNA, no difference was seen between WT and IL-10-/- mice. In addition, splenocytes from IL-10-/- mice produced elevated levels of nitric oxide (NO) compared to WT mice, and NO has been shown to inhibit activity of interleukin-1 converting enzyme (ICE), which is required for IL-18 production. However, the addition of an inhibitor of NO production did not alter the levels of IL-18 produced. Finally, analysis of the levels of cytokine mRNA of macrophages stimulated with LPS and IFN-gamma revealed that although IL-10 is a potent inhibitor of IL-12 mRNA accumulation, it did not inhibit IL-1beta or IL-18. Together, these data indicate that IL-10 is not an inhibitor of the production of IL-18.
authors.affiliation: Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, 3800 Spruce Street, Philadelphia, PA 19104-6050, USA.
authors.forename: Valerie P
authors.initials: VP
authors.lastname: Zediak
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Hunter
mesh_terms: D000818:Animals; D016207:Cytokines / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D016753:Interleukin-10 / Q000378:metabolism / Q000502:physiology*; D018664:Interleukin-12 / Q000378:metabolism; D020382:Interleukin-18 / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D008822:Mice, Transgenic; D009569:Nitric Oxide / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012260:Ribonucleases / Q000378:metabolism; D013154:Spleen / Q000166:cytology / Q000378:metabolism; D013997:Time Factors; D014122:Toxoplasma / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D016207:Cytokines; D020382:Interleukin-18; D012333:RNA, Messenger; D016753:Interleukin-10; D018664:Interleukin-12; D009569:Nitric Oxide; D012260:Ribonucleases