Regulation of interleukin-12 expression in human monocytes: selective priming by interferon-gamma of lipopolysaccharide-inducible p35 and p40 genes

Abstract

Interleukin-12 (IL-12) is a monocyte/macrophage-derived cytokine that is critical for T lymphocyte and natural killer cell activities and functions. In this study, we examined the regulation of IL-12 expression by human monocytes in response to bacterial lipopolysaccharide (LPS). Several novel aspects of IL-12 induction from monocytes were shown. Optimal expression of IL-12 mRNA and bioactivity required specific priming of monocytes by interferon-gamma (IFN-gamma) before LPS stimulation. Granulocyte-macrophage colony-stimulating factor (GM-CSF) provided an equivalent priming stimulus for LPS-induced tumor necrosis factor (TNF) and IL-12 p40 mRNA, but primed poorly for LPS-inducible p35 message and secreted IL-12 activity. Macrophage colony-stimulating factor (M-CSF), although a potent survival factor for monocytes, showed no priming activity for IL-12 production. Time course experiments demonstrated independent regulation of p40 and p35 by IFN-gamma and LPS. LPS inducibility of p40 expression required only a brief exposure to IFN-gamma (2 hours), while prolonged exposure (+/- 24 hours) to IFN-gamma resulted in diminishing levels of p40 mRNA. p35 inducibility (by LPS) required a longer exposure to IFN-gamma (8 to 16 hours), and continued to be inducible up to 40 hours following IFN- gamma priming. Both mRNAs were rapidly induced (1 to 2 hours) in IFN- gamma-primed monocytes; p35 message reached a plateau by 2 hours, while p40 continued to accumulate. Finally, both p40 and p35 were directly induced by LPS in the presence of cycloheximide. These results indicated that both p40 and p35 are LPS-inducible in monocytes following IFN-gamma pretreatment, and that the regulated expression of p35 controls the level of active IL-12 protein in purified human monocytes. The selectivity of priming by IFN-gamma is in accord with a putative role for IL-12 in the initiation and amplification of TH1-type responses.

CARD15 variants determine a disturbed early response of monocytes to adherent‐invasive Escherichia coli strain LF82 in Crohn's disease

“…Only minimal secretion of IL-12 was detected, merely measurable after 20 h of infection, most probably due to the absence of inferno gamma (IFNγ) in these purified monocyte cultures. IFNγ normally provides a positive loop for IL-12 induction (Hayes et al, 1995;Ma et al, 1996;Liu et al, 2003). There were no differences between the three different SNPs but interestingly, a gene-dose effect was noted for IL-1β and IL-6.…”

Developmental changes in interleukin‐12‐producing ability by monocytes and their relevance to allergic diseases

“…We chose the whole-blood culture, because production of IL-12 was low in isolated cells as reported previously [5]. Pre-incubation with IFN-g was necessary to detect LPSinduced IL-12 synthesis as reported previously [12]. From our preliminary study regarding incubation period, the condition of 22 h with LPS after 2 h priming with IFN-g was suf®cient (data not shown).…”

Expression of Epstein–Barr virus‐induced gene 3 and other interleukin‐12‐related molecules by human intestinal epithelium

“…Moreover, intestinal epithelial cells can function as antigen-presenting cells 1 and produce cytokines, chemokines and other immune mediators that are important in signalling the onset of mucosal immune and inflammatory responses. [2][3][4][5][6][7][8] Members of the interleukin (IL)-12 family of proteins are produced by antigen-presenting cells including monocytes, macrophages and dendritic cells [9][10][11][12][13][14] and have an important role in the development of T helper 1 (Th1)polarized CD4 + T-cell responses. The prototypic member of this family, IL-12p75, is a heterodimeric cytokine that contains two independently regulated subunits, IL-12p40 and IL-12p35.…”

“…The prototypic member of this family, IL-12p75, is a heterodimeric cytokine that contains two independently regulated subunits, IL-12p40 and IL-12p35. 9,10,15,16 IL-12p75 stimulates interferon-c (IFN-c) production by T and natural killer (NK) cells and has a key role in the induction and maintenance of Th1 immune responses. [17][18][19][20][21] Additional members of the IL-12 family of proteins share significant homology with IL-12p35 or IL-12p40.…”