Cytokine mRNA levels in antigen-stimulated peripheral blood mononuclear cells

Levels of cytokine mRNA coding for granulocyte-macrophage colony-stimulating factor (GM-CSF), interferon-gamma (IFN-gamma), interleukin (IL) 2, IL 1 beta, IL 4 or IL 6 have been measured by Northern blot analysis after antigen stimulation. As source for RNA we used peripheral blood mononuclear cells (PBMC) from donors which showed a proliferative response after tetanus toxoid or Candida albicans stimulation. For comparison PBMC were also stimulated with lectins and anti-CD3 antibody. With some variations among donors, antigens clearly induced measurable levels of IFN-gamma, GM-CSF and IL 2 mRNA. Increased levels for IL 6 were also detected after antigen stimulation. In contrast to polyclonal T cell stimuli, antigens showed delayed kinetics of mRNA steady-state levels and resembled in this respect more closely the stimulation with pokeweed mitogen. Thus, cytokine mRNA levels may be assessed in unfractionated PBMC after antigen stimulation. The two tested antigens also clearly show a cytokine pattern distinct from that induced in polyclonal stimulations such as anti-CD3.

Mitogenic activation of human T cells induces two closely related genes which share structural similarities with a new family of secreted factors

Previously we have isolated about 60 novel cDNA clones whose corresponding mRNAs are induced by mitogenic activation in human peripheral blood T cells. Here we describe the primary structure and regulation of two such cloned genes, pAT 464 and pAT 744, which may encode new lymphokines/cytokines. Similar to IL-2, both genes require the synergy of agents such as PHA and PMA for optimal expression, and, in addition, the induction of both is sensitive to the immunosuppressive drug cyclosporin A. The two genes can be expressed in T cells, B cells, and the promyelocytic cell line HL60, but they are not expressed in human fibroblasts, suggesting that their expression is restricted to hematopoietic lineages. The predicted peptides encoded by these two clones feature hydrophobic N-terminal leaders characteristic of secreted proteins. The predicted size of both proteins is about 8 kDa upon cleavage of the putative leader peptide. pAT 464 and pAT 744 are very similar to each other and also share some critical amino acid similarity with a newly emerging family of secreted factors including connective tissue activating factor III, platelet factor 4, an IFN-gamma-induced factor, macrophage inflammatory protein, and a factor chemotactic to neutrophils (3-10C, monocyte-derived neutrophil chemotactic factor, neutrophil-activating factor). Some of these factors have been shown to display functions associated with an inflammatory response and/or have mitogenic activities. Collectively, the data presented here suggest that pAT 464 and pAT 744 encode novel lymphokines/cytokines which may play roles during an immune response similar to those enacted by these structurally related factors.

CD28 activation pathway regulates the production of multiple T-cell-derived lymphokines/cytokines

CD28 is a 44-kDa glycoprotein expressed as a homodimer on the surface of a major subset of human T cells. Previous studies have demonstrated that the binding of monoclonal antibodies to the CD28 surface antigen can augment the proliferation of purified human T cells stimulated with suboptimal doses of mitogens or anti-T-cell receptor/CD3 complex antibodies. In this report, we show that CD28 stimulation augments T-cell immune responses by specifically inducing a 5- to 50-fold enhancement in the expression and secretion of interleukin 2, tumor necrosis factor type alpha, lymphotoxin, interferon gamma, and granulocyte-macrophage colony-stimulating factor in normal human T cells stimulated to proliferate by crosslinking of the T-cell receptor/CD3 complex. This CD28-mediated induction of lymphokine/cytokine gene expression occurred even in T cells stimulated with optimal concentrations of mitogens or anti-T-cell receptor/CD3 antibodies, although under these conditions CD28 activation failed to enhance the proliferative response. The activation pathway induced by stimulation of CD28 is distinct from other biochemical pathways that induce lymphokines/cytokines because CD28 stimulation can induce lymphokine/cytokine gene expression in the presence of the immunosuppressant cyclosporine. Together these data suggest that the CD28 cell surface molecule is part of a distinct activation pathway that specifically modulates the expression of multiple lymphokine/cytokine genes.

Specific assays for cytokine production by T cells

Recent advances in understanding of cytokine function have indicated the need for more stringent cytokine assays, and have at the same time provided the information and tools necessary for establishing monospecific assays for a number of T cell-derived cytokines. Monoclonal antibodies are invaluable for improving the specificity of bioassays, both by removing unwanted activities, and in the most stringent assays, for confirming the identity of the cytokine detected. Several cytokines can also be directly measured by ELISA techniques using monoclonal antibodies.

AIDS-Kaposi's sarcoma-derived cells express cytokines with autocrine and paracrine growth effects

When grown in vitro, cells from Kaposi's sarcoma lesions of AIDS patients (AIDS-KS cells) constitutively release several growth promoting activities. When inoculated into nude mice, the AIDS-KS cells induce a KS-like lesion of mouse origin. Here it is shown that the AIDS-KS cells express messenger RNA for a complex mixture of cytokines that correlate with several of the biological activities of these cells. Basic fibroblast growth factor, which is a potent angiogenic factor, and interleukin-1 messenger RNAs are expressed at very high levels and seem to account for a large proportion of the activities, since their corresponding proteins are released in biologically active form into the culture media where they induce autocrine and paracrine growth effects.

Endotoxin-induced cytokine gene expression in vivo. I. Expression of tumor necrosis factor mRNA in visceral organs under physiologic conditions and during endotoxemia

Tumor necrosis factor (TNF) mRNA was detected by Northern blotting in whole-organ homogenates of the spleen, liver, kidney, lung, and small bowel in naive and saline-injected control rats, supporting the hypothesis that TNF mRNA is present in vivo in a preformed intracellular pool. TNF mRNA in endotoxin-treated rats as quantitated by densitometry of the ratio of TNF mRNA to actin mRNA in Northern blots was present in increased quantity in the liver, kidney, and lung (1.6-2.9 times over time zero levels) at 15 minutes and increased quantity in the spleen, liver, and kidney (1.3-1.9 times over time zero levels) at 30 minutes. The kinetics of endotoxin-induced TNF gene expression are consistent with the relatively transient peak of serum TNF protein levels reported by previous investigators to occur approximately 1 hour after injection of endotoxin. Because TNF mRNA appeared ubiquitous in the organs of control rats examined and because the endotoxin-induced increase in TNF mRNA was relatively small, endotoxin may induce the expression of the TNF protein in serum not only by increasing TNF mRNA levels but perhaps more importantly by a posttranscriptional mechanism. The presence of a preformed pool of TNF mRNA may teleologically be viewed as a mechanism to increase the rapidity of the host's response to sepsis.

Monokines: stimulatory and inhibitory regulator molecules of myelopoiesis in vitro

The conditions for monocytes to secrete molecules that are involved in myelopoiesis, i.e. Colony Stimulating Factors (CSFs), Interleukin-1 (IL-1) and Tumor Necrosis Factor-alpha (TNF-alpha) were investigated. Whereas secretion of these molecules by monocytes is negligible in a quiescent state, activation of monocytes with Interferon-gamma (IFN-gamma) results in mRNA accumulation and subsequent protein secretion of CSF for granulocytes (G-CSF) and for monocytes (M-CSF). Under identical conditions mRNA-transcripts of TNF-alpha, IL-1-alpha and IL-1-beta genes were induced. Whereas IFN-gamma induces secretion of TNF-alpha protein, protein secretion of IL-1 by monocytes failed to occur in response to an IFN-gamma stimulus. However, the presence in culture of IFN-gamma in combination with TNF-alpha induced secretion of IL-1. Although IL-1 regulates the production of CSF for granulocytes and monocytes (GM-CSF) by IL-1 receptive T-lymphocytes, and is therefore involved in upregulatory mechanisms of myeloid growth, it may be able to suppress growth of myelopoietic progenitor cells (MPC) as well, when hematopoietic cultures are depleted of cells, that have the potential to secrete CSFs. Similarly, IFN-gamma, although being a major inducer of CSF secretion by monocytes, was shown to inhibit myeloid colony growth when exposed to purified MPC and allowed to synergize with TNF-alpha.

The expression of cytokines in the organs of normal individuals: role in homeostasis. A review

Cytokines such as interferons (IFN), tumor necrosis factor (TNF), interleukins (IL), and growth factors are suggested to occupy a central position in a putative network of cytokine interactions in vivo which act to maintain homeostasis in normal tissues. Recent results suggest that specific interferon genes are transcribed at low levels in the organs of normal individuals in the apparent absence of virus infection while other interferon genes remain unexpressed in the same tissues. In contrast, the genes of cytokines such as IL-1, TNF, and IFN beta-2/IL-6 appear to be regulated in vivo in a manner quite distinct from that of interferon genes as these cytokines are expressed at high levels in the spleen, liver, and peripheral blood leukocytes of normal individuals. The localized production and action of a cytokine could provide a mean of attaining specificity of action for multifunctional cytokines. Thus under physiological conditions the activity expressed by a particular cytokine may be determined by tissue specific interactions which may in turn be influenced by other cytokines. Abnormal production of a particular cytokine would lead to a perturbation of homeostasis and may contribute to the pathogenesis of certain autoimmune or inflammatory diseases.