Synergistic induction of interleukin-6 production and gene expression in human thymic epithelial cells by LPS and cytokines.
We examined the ability of LPS and several cytokines (TNF-alpha, IL-1-beta, IFN-gamma, IL-4) to modulate IL-6 production by cultured human thymic epithelial cells (TEC). IL-6 activity was measured by the hybridoma growth factor biological activity. Moderate but detectable IL-6 activity was spontaneously produced in the presence of serum proteins. LPS as well as the cytokines TNF-alpha and IL-1-beta was a potent inducer of IL-6, increasing, respectively, IL-6 levels by 9-, 28-, and 75-fold (mean values) while IL-4 and IFN-gamma provoked no significant effect. Interestingly, clearly different kinetics were observed for IL-6 induction by the various activation agents, the maximal effect being reached at 24, 48, and 72 hr, respectively for LPS, TNF-alpha, and IL-1-beta. Moreover, a synergistic effect of TNF-alpha and either LPS or IL-1-beta was observed. Indeed, TEC incubated with the cytokines in combination at optimal doses produced 5- to 170-fold more IL-6 than TEC stimulated with the cytokines individually. Neutralizing anti-IL-6 polyclonal and monoclonal antibodies completely blocked hybridoma proliferation stimulating activity of TEC supernatants; thus, implying that this activity is essentially due to IL-6. In situ hybridization analysis of cytocentrifuged TEC with an mRNA antisense probe specific for human IL-6 and labeled with 35S demonstrated that up to 90% of TEC could be induced to express the IL-6 gene. Computer-aided quantification of IL-6 mRNA levels indicated that upon stimulation with TNF-alpha combined to LPS, both the numbers of cells expressing IL-6 mRNA and the amounts of cytoplasmic IL-6 mRNA per cell were increased. Taken altogether these results demonstrate that LPS and/or cytokines can modulate and synergistically stimulate IL-6 production. In addition to a possible role in regulating normal thymic T cell activation, the IL-6 produced by TEC could be of pathophysiological relevance in disregulated situations such as in hyperplastic thymuses from patients with myasthenia gravis.
CNRS URA-1159, Hôpital Marie Lannelongue, Le Plessis Robinson, France.
S
S
Cohen-Kaminsky
R M
RM
Delattre
O
O
Devergne
P
P
Rouet
D
D
Gimond
S
S
Berrih-Aknin
P
P
Galanaud
D002675:Child, Preschool; D004357:Drug Synergism; D004848:Epithelium / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects*; D006801:Humans; D007223:Infant; D007375:Interleukin-1 / Q000494:pharmacology*; D015850:Interleukin-6 / Q000096:biosynthesis* / Q000235:genetics / Q000276:immunology; D008070:Lipopolysaccharides; D012333:RNA, Messenger / Q000032:analysis; D013950:Thymus Gland / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
D007375:Interleukin-1; D015850:Interleukin-6; D008070:Lipopolysaccharides; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha