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BACKGROUND: Interleukin-6 (IL-6), a pluripotent cytokine, has traditionally been considered the product of proinflammatory cells. However, many other cell types have been shown to produce IL-6. Since intestinal inflammation is commonly associated with a vigorous systemic inflammatory response, we hypothesized that intestinal epithelial and smooth muscle cells might contribute to that response by producing IL-6. We therefore studied the capacity of differentiated human intestinal epithelial and smooth muscle cell lines to produce IL-6 in response to various proinflammatory stimuli. MATERIALS AND METHODS: CCL-241, a human intestinal epithelial cell line, and HISM, a human intestinal muscle cell line, were grown to confluency and then treated for 24 h with various concentrations of lipopolysaccharide, Clostridium difficile culture extract containing both toxin A and toxin B, recombinant human tumor necrosis factor-alpha (TNF-alpha), or recombinant human interleukin-1 beta (IL-1beta). Supernatants were then collected for IL-6 determination using an enzyme-linked immunosorbent assay. Cell numbers were determined using a Coulter counter. For comparison, parallel studies were performed using phorbol ester-primed U-937 and THP-1 human macrophage cell lines. RESULTS: Both human intestinal epithelial and smooth muscle cells produced IL-6 under basal conditions. In HISM cells, but not in CCL-241 cells, IL-6 release was increased slightly by treatment with C. difficile culture extract containing both toxin A and toxin B and with lipopolysaccharide. In both cell lines, IL-6 production was profoundly stimulated by treatment with IL-1beta and less so with TNF-alpha. Combinations of high-dose TNF-alpha and IL-1beta may have a slightly additive, but not synergistic, effect on IL-6 release. The amount of IL-6 produced by IL-1-stimulated intestinal cell lines was 70-fold higher than that produced by stimulated macrophage cell lines. CONCLUSIONS; Both intestinal epithelial and smooth muscle cells demonstrate the ability to release significant amounts of IL-6. The profound response to IL-1beta and TNF-alpha stimulation by both cell lines suggests that human intestinal parenchymal cells, influenced by paracrine mediators liberated from proinflammatory cells, might significantly contribute to the overall systemic inflammatory response by producing IL-6.

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The time course of Ca(2+)-dependent amylase secretion from alpha-toxin-permeabilized rat pancreatic acini was biphasic, consisting of an initial burst of secretion, which lasted approximately 2.5 min, followed by a slower, sustained release of amylase. The initial, rapid phase of secretion did not appear to require MgATP, whereas the second, sustained phase of secretion was entirely MgATP dependent. The initial, rapid, apparently MgATP-independent response was labile in the prolonged absence of MgATP and was abolished when the acini were metabolically poisoned before permeabilization. These findings suggest that the initial phase of secretion does not require the presence of MgATP but is actually dependent on an MgATP-requiring event that occurred within the acini before permeabilization. Our studies also demonstrated that MgATP acts before Ca2+ to prime amylase secretion. Thus the initial, rapid phase of secretion most probably reflects release via exocytotic sites primed by MgATP before permeabilization. The slower kinetics of the second, sustained phase of secretion may, at least in part, reflect the repriming of the exocytotic machinery. The results of these studies also indicate that Ca(2+)-dependent secretion (regulated exocytosis) in the pancreatic acinar cell is composed of at least two biochemically distinct steps. The first step is MgATP dependent and primes exocytosis and is followed by a Ca(2+)-dependent, but MgATP-independent, step that triggers exocytosis.

Streptolysin O (SLO)-permeabilized pancreatic acini are now frequently used to study regulated exocytosis in the exocrine pancreas. In this paper we introduce alpha-toxin as a possible alternative permeabilization agent to SLO. Both alpha-toxin and SLO are bacterial cytolysins, but the membrane pores generated by SLO are approximately 5-10 times larger than those formed by alpha-toxin. The Ca2+ requirements for amylase secretion from both types of permeabilized acini were identical, maximal amylase secretion being obtained at 30 microM Ca2+ with an effective concentration of approximately 3-4 microM Ca2+ producing 50% of the maximal response. However, Ca(2+)-stimulated amylase secretion from the SLO-permeabilized acini stopped after 10-15 min, unlike secretion from the alpha-toxin-permeabilized cells, which continued for at least 50 min. The rapid cessation of secretion from the SLO-treated acini reflects the rapid decline in the responsiveness of the cells observed after permeabilization. This decline in Ca(2+)-dependent secretion appears to be due to the loss of cytosol, since addition of purified rat brain cytosol to nonresponsive SLO-permeabilized acini reconstituted regulated secretion. Because alpha-toxin-permeabilized acini maintained their responsiveness, the cytosolic factors lost from the SLO-permeabilized cells must be retained within the toxin-treated cells. The reconstitutive activity of the brain cytosol was nondialyzable but heat and trypsin sensitive, suggesting that the factors responsible are proteins. Of the cytosols screened (brain, liver, spleen, muscle, and lacrimal) only those prepared from brain or lacrimal gland reconstituted Ca(2+)-dependent amylase secretion.(ABSTRACT TRUNCATED AT 250 WORDS)