| Abstract: | It was previously shown that avidin, a glycoprotein secreted in vivo by chicken oviduct, is produced by cultured transformed or damaged chicken embryo fibroblasts 27]. This report demonstrates synthesis and secretion of large amounts of avidin by macrophages isolated from chicken yolk sac. Avidin was secreted to the culture medium as shown by immunoprecipitation of metabolically labeled proteins. In the culture medium of macrophages the avidin concentration (up to 47.5 +/- 0.5 microgram/mg cellular protein) exceeded, in agreement with previous findings, that of fibroblasts (up to 7.3 +/- 0.7 microgram/mg) infected with transforming retroviruses (Rous sarcoma virus, its mutants temperature sensitive for transformation and OK 10 virus). No difference between the macrophage avidin and the egg white avidin was detected by both the heat-induced 14C] biotin exchange assay and immunoblotting (subunit Mr = 15600). By immunofluorescence 10 to 20% of the cells were positive for avidin, independent of the time in culture (1-30 days). The staining pattern varied between dense or granular perinuclear and strong reticulo-granular fluorescence throughout the cytoplasm. Double staining for avidin and the Golgi region by wheat germ agglutinin showed that avidin is concentrated, and might be processed, in the Golgi complex. The production of avidin by macrophages supports a role for avidin in host defence mechanisms. |
