Acute-Phase Proteins in Response to Tumor Growth

Abstract

This study has evaluated the relationship between tumor growth and induction of acute-phase proteins. It has also determined whether an intact cellular immunity is obligatory for a fully expressed acute-phase plasma protein response in the presence of a highly antigenic tumor. Quantitatively, acute-phase responses (protein synthesis, plasma concentrations, hepatic RNA content, anorexia) were proportional to tumor burden. Anti-inflammatory drugs (indomethacin 1 μg/g body wt, dexamethasone 0.5 μg/g body wt) had no direct effect on the attenuation of the systemic acute-phase responses, but did affect them indirectly by decreasing tumor growth. Immune suppression (cyclosporine A at 20 or 60 μg/g body wt) had no effect on either acute-phase reactions or local tumor growth. In endotoxin-stimulated (lipopolysaccharide) normal mice, immune suppression aggravated anorexia and caused high mortality, while dexamethasone partly reversed these effects in endotoxin-stimulated mice. Plasma levels of acute-phase proteins correlated to circulating levels of IL-6 in untreated tumor-bearing mice, but this relationship was not obvious in either drug-treated tumor-bearing or endotoxin-stimulated mice. Tumor tissue induced the synthesis of different acute-phase proteins compared to endotoxin. However, disintegrated normal liver tissue induced the synthesis of serum amyloid protein to the same extent as the growing tumor. This effect was primarily associated with the mitochondrial/lysosomal and microsomal liver cell fractions. In conclusion, the overall acute-phase protein response is not a modulating factor of tumor growth. It is secondary to such factors as tumor burden, necrotic tissue, and destruction of normal tissue matrix by tumor invasion. The acute-phase protein response is qualitatively different in tumor disease and endotoxinemia, and it is not critically dependent on normal cellular immunity for its full expression.