Macrophage and monocyte IL-1 beta regulation differs at multiple sites. Messenger RNA expression, translation, and post-translational processing.
Maturation of blood monocytes into macrophages is accompanied by a number of functional changes including decreased IL-1 beta release in response to LPS. This limitation has previously been ascribed to transcriptional regulation. However, in seeming conflict with the observed depression in IL-1 beta mRNA levels, recent work demonstrates increased intracellular IL-1 beta in macrophages. Therefore, the present study sought to explain these differences by comparing IL-1 beta production from autologous alveolar macrophage and blood monocyte pairs at multiple regulatory sites, including endotoxin responsiveness, mRNA expression, protein translation, and post-translational processing. Macrophages did not differ from monocytes in endotoxin sensitivity, but when analyzed by both ELISA and Western blot, were confirmed to have limitations in IL-1 beta release. Gene expression studies demonstrated that at 4 h, macrophage IL-1 beta steady state mRNA levels were 3-fold lower than the monocyte's. However, total IL-1 beta protein production, as measured by [35S]methionine labeling with immunoprecipitation, demonstrated three- to sixfold higher amounts in macrophages at comparable time points. The enhanced protein production in the face of relatively low mRNA levels suggests that macrophages translate IL-1 beta mRNA more efficiently. Furthermore, characterization of IL-1 beta release into supernatants revealed that whereas monocyte release occurred early, represented 5 to 20% of the intracellular amounts, and contained largely processed IL-1 beta, macrophage release was delayed, represented 1 to 5% of the intracellular amounts, and contained primarily unprocessed IL-1 beta. Taken together, these data demonstrate that the limitations in alveolar macrophage IL-1 beta release occur due to slower export and conversion of 35- to 17-kDa protein and are not due to differences in sensitivity to endotoxin or to transcriptional control mechanisms.
Herzyk
D J
DJ
Department of Internal Medicine, Ohio State University, Columbus 43210.
Allen
J N
JN
Marsh
C B
CB
Wewers
M D
MD
D015152:Blotting, Northern; D015153:Blotting, Western; D003609:Dactinomycin / Q000494:pharmacology; D004306:Dose-Response Relationship, Immunologic; D004731:Endotoxins / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay; D005786:Gene Expression Regulation / Q000502:physiology; D006207:Half-Life; D006801:Humans; D007375:Interleukin-1 / Q000378:metabolism*; D008264:Macrophages / Q000378:metabolism*; D009000:Monocytes / Q000378:metabolism*; D014176:Protein Biosynthesis / Q000502:physiology*; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D012333:RNA, Messenger / Q000096:biosynthesis*
D004731:Endotoxins; D007375:Interleukin-1; D012333:RNA, Messenger; D003609:Dactinomycin