Biosynthesis of the third component of complement in rat liver epithelial cell lines and its stimulation by effector molecules from cultured human mononuclear cells |
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Authors: | Michel Guiguet Marie-France Exilie Frigere Marie-Claire Dethieux Yves Bidan Gérard Mack |
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Institution: | (1) Laboratoire de Biochimie Médicale, Unité de Recherche INSERM U208, Faculté de Médecine, 7 boulevard Jeanne d'Arc, 21033 Dijon Cedex, France |
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Abstract: | Summary Rat liver epithelial cell lines, growing in a serum-supplemented medium, synthesize and secrete into the culture medium the
third component of complement (C3). We studied the regulation of C3 production in this system. We found that human peripheral blood mononuclear leukocytes in culture released one or more soluble
factors which stimulated rat liver epithelial cells to produce increased quantitites of C3. This stimulting effect was strongly enhanced when the mononuclear cell cultures were treated with phytohemagglutinin, a
T-lymphocyte mitogen. The factor(s) failed to enhance C3 biosynthesis by rat dermal fibroblasts, which are known to produce this protein. This reveals a tissue-specific differential
response between the fibroblasts and the liver epithelial cells. The physical and chemical characteristics, such as heat sensitivity,
2.8M ammonium sulphate precipitation, and lower activity after digestion by proteases unambiguously indicate that the effector
molecules are proteins. When the crude supernatant of mononuclear leukocytes was fractionated by gel filtration, the stimulating
factor(s) eluted as two peaks with apparent molecular weight of 25 to 60 and 15 to 20 kdalton, respectively. As to the cellular
origin of the C3-stimulating factor(s), several observations were made: (a) in separate cultures containing either T-cells or monocyte-enriched
populations from the same sample of blood mononuclear cells, no activity was detected in the presence or absence of phytohemagglutinin,
(b) conditioned media from each of these cultures could not substitute for the corresponding intact cell populations, and
(c) the addition of purified T-cells to the monocyte-enriched population in the presence of phytohemagglutinin restored the
production of the stimulating activity by the mixed culture. Finally, experiments were carried out to verify whether monokine
interleukin 1 affects the hepatic C3 biosynthesis. It was demonstrated that interleukin 1 enhanced this biosynthesis, but could not completely substitute for
conditioned medium from stimulated mononuclear cells. |
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Keywords: | rat liver epithelial cell line third component of complement human cytokines |
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