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The early response to inflammation is characterized by the synthesis of a variety of proteins under cytokine and glucocorticoid control. During episodes of infection or inflammation, a secretory phospholipase A2 (sPLA2) appears in the circulation along with a variety of acute-phase proteins (APP), suggesting possible common regulatory elements amongst sPLA2 and APP. Using the human hepatoma line, HepG2, regulation of sPLA2 expression was examined in relation to synthesis of HP and ACH. The patterns of induction of sPLA2, HP and ACH were distinct for each of IL- 1, tumour necrosis factor (TNF) and IL-6, oncostatin M, IL-11 and leukaemia inhibitory factor. Dexamethasone had an enhancing effect on IL-6-induced expression of HP and ACH, but inhibited sPLA2 expression by 50%. Both 8-bromo-cAMP and dibutyryl cAMP increased sPLA2 expression (48.8-fold and 64.2-fold, respectively), whereas KT5720, an inhibitor of protein kinase A, down-regulated cytokine-induced sPLA2 synthesis by 51%. These data show that a panel of cytokines induced varying patterns of up-regulation of sPLA2, ACH and HP. Although dexamethasone potentiated IL-6-induced APP expression in HepG2 cells, it suppressed sPLA2 expression in a dose-dependent manner. In several respects, sPLA2 regulation is similar to that of HP and ACH, but a notable difference is the reciprocal effect of glucocorticoids on sPLA2 expression compared with that of ACH and HP.

To investigate the contribution of IL-11 and LIF to acute-phase protein (APP) production, we first analysed the effects of IL-11 and LIF on production of C-reactive protein (CRP), fibrinogen, and haptoglobin by human primary hepatocytes. We also measured the serum levels of IL-11, LIF, and CRP in serum from patients with inflammatory rheumatic diseases to assess the role of these cytokines in the APP response in vivo. We included patients with conditions associated with a high APP response such as rheumatoid arthritis (RA) or spondylarthropathy (SpA), and others usually associated with a weak APP response such as systemic lupus erythematosus (SLE), in order to investigate whether these cytokines could account for the differences in APP responses. Our results showed that IL-11 and LIF induced only minimal stimulation on production of APP by human primary hepatocytes compared with IL-6, known as the major inducer. Serum levels of CRP were elevated in RA and SpA, and significantly higher than in SLE patients. Despite the presence of a high APP response in some of our patients and despite the fact that we used sensitive assays to measure IL-11 and LIF, serum levels of both cytokines were not detected in any of the tested sera. In conclusion, our results show that circulating levels of IL-11 or LIF do not contribute significantly to the production of APP in vivo, and that they do not account for the difference in APP response between SLE and other inflammatory rheumatic diseases.

IL-6, tumour necrosis factor-alpha (TNF-alpha) and IL-1 are thought to be the key mediators of the acute phase response although much of the evidence is based on in vitro studies. It is not clear to what extent each of the acute phase proteins are regulated in vivo by each of these cytokines. The aim of this study was to examine the effects of IL-6 treatment in eight patients with cancer on the concentrations of an extensive range of positive and negative acute phase proteins. It was part of a larger investigation to assess the value of IL-6 in the management of chemotherapy-induced thrombocytopenia. IL-6 was administered by a daily subcutaneous injection for 7 days at a dose level of 1, 3, or 10 micrograms/kg/day. Increases in the positive acute phase proteins, serum amyloid A, C-reactive protein, alpha 1-acid glycoprotein, alpha 1-antichymotrypsin, haptoglobin, alpha 1-antitrypsin, fibrinogen, complement component C3, and caeruloplasmin, were observed, with the greatest incremental changes and fastest responses being seen for C-reactive protein and serum amyloid A protein. The negative acute phase proteins transferrin, transthyretin and retinol binding protein all fell to a nadir within 48-96 h after the first IL-6 injection. Increases in complement component C4 were only found in two patients, which may be related to the increase in circulating TNF-alpha concentrations found only in these patients. This study has therefore shown that IL-6 is capable of causing changes in the majority of acute phase proteins in vivo. Although secondary induction of TNF-alpha was not observed in the majority of patients examined, it is still possible however that other cytokines involved in regulation of the acute phase response, such as IL-1, may have been induced and contributed to the overall response.

The effect of Lps locus and IL-6 on the production of SU (previously termed gp70), a mouse endogenous retroviral gene product, was studied. Back-cross studies using the progeny between (NZB x C3H/HeJ)F1 and C3H/HeJ mice indicate that the basal level of SU is not associated with the Lps locus on chromosome 4. Lipopolysaccharide (LPS) mitogen response-negative mice did not show the enhancement of serum SU production after LPS injection. Spleen cells from LPS-mitogen response-positive but not from negative mice showed increase of IL-6 synthesis in the presence of LPS. Since IL-6 may be involved in the production of serum SU, we tested the effect of IL-6 in a primary hepatocyte culture system. SU production was clearly enhanced in the presence of recombinant IL-6, indicating that IL-6 induced by LPS can enhance the expression of retroviral genome.

Interleukin-6 (IL-6, BSF-2 or IFN-beta 2) is thought to be the major regulator of the acute-phase protein response that follows tissue injury and inflammation, with interleukin-1 (IL-1), tumour necrosis factor and more recently, LIF or HSF III, slightly stimulatory on only certain acute phase proteins. The synthesis of the major acute-phase protein SAA, originally described as being synthesized in response to IL-1, has been claimed recently to be mainly under IL-6 regulation. Our results show that in the human hepatoma cell line HuH-7, IL-1 is the major stimulating cytokine increasing SAA synthesis by a factor in excess of 100-fold. We also show that under most conditions interleukin-6 and tumour necrosis factor stimulate additively in combination with IL-1. Isoelectric focusing has demonstrated that SAA1 and SAA2 alpha are expressed but not SAA2 beta. The HuH-7 cell line is IL-6 responsive since haptoglobin is stimulated mainly by IL-6.

The effects of various cytokines on synthesis and microheterogeneity of carbohydrate structure of alpha 1-proteinase inhibitor (PI) and alpha-fetoprotein (AFP) in the human hepatoma cell lines Hep 3B and Hep G2 were studied. In both lines, crude cytokine preparations from LPS-activated human monocytes (CM) and several cell lines led to increased PI and decreased AFP synthesis, while recombinant interleukin 1 (IL-1), recombinant tumor necrosis factor (TNF) and hepatocyte stimulating factor preparations (HSF) affected AFP but not PI production. Several of the crude cytokine preparations, but not IL-1, TNF, or HSF, caused Hep 3B cells to secrete forms of PI and AFP showing increased reactivity with Con A upon testing by affinity electrophoresis, while decreased reactivity with Con A was seen in these proteins secreted by Hep G2 cells. Determination of molecular size of PI inducing activity in CM showed a sharp peak at about 17 kD while AFP inhibiting activity was present in a very broad range of molecular size fractions maximal at 17-30 kD. Changes in patterns of glycosylation of these proteins were attributable to cytokines of about 30 kD in Hep 3B and 44 kD in Hep G2 cells. These findings demonstrate the existence of a family of glycosylation regulating cytokines, and suggest that distinct mechanisms within hepatocytes, responsive to different cytokines, may lead to increased or decreased Con A binding of glycoproteins and to altered gene expression.

The Sgp-1c trait is associated with H-2s and relates to the small content of serum gp70 as well as the lack of serum gp70 responsiveness to lipopolysaccharide (LPS). Northern hybridization of RNA from B10.S liver and its hybrid with NZB showed that the suppression of gp70 in Sgp-1c carrying mice can be regulated at the transcriptional level. However, the inheritance of this trait shows the complicated manner of segregation in certain crosses. All (B10.S x NZB) F1 hybrid mice and F1 x B10.S back-cross mice had low amounts of serum gp70 and did not respond to LPS with increased levels of serum gp70. In contrast, F1 x NZB back-cross progeny varied widely in serum gp70 levels. The serum gp70 levels of most F1 x NZB back-cross mice was increased by LPS, although the range of increases was broad. These results indicate that the Sgp-1c alone is not sufficient to lower serum gp70 levels, unless B10 background is present. The expression of Sgp-1 system, which is linked with the H-2 region, requires non-H-2-linked genes.