REGULATION OF A MURINE MACROPHAGE HEMAGGLUTININ (SHEEP ERYTHROCYTE RECEPTOR) BY A SPECIES-RESTRICTED SERUM FACTOR

  • 1 December 1988
    • journal article
    • research article
    • Vol. 65  (4) , 515-522
Abstract
The mechanisms which generate heterogeneity amongst resident tissue macrophages (M.vphi.) are poorly understood. In previous study was described a novel mouse M.vphi. haemagglutinin, which binds unopsonized sheep erythrocytes. This sheep erythrocyte receptor (SER) is expressed at high levels on stromal M.vphi. from bone marrow and lymph nodes, but at low levels on M.vphi. from serous cavities and broncho-alveolar spaces. In this paper we demonstrate that a species-restricted factor in mouse serum is required in vitro for optimal maintenance of SER on resident bone marrow M.vphi. and for its induction on M.vphi. populations which normally lack this receptor. Using thioglycollate-elicited peritoneal M.vphi., induction of SER by mouse serum was dose-dependent, reached maximal levels by 3-4 days, required the continuous presence of mouse serum, and was fully reversible. Re-expression following trypsinization was inhibited by cycloheximide, showing that protein synthesis by M.vphi. was necessary. Using a quantitative microtitre plate assay to measure levels of the inducing activity (SER-IA) in different samples, it was found to be heat-labile, non-dialysable, precipitable by polyethylene glycol and inactivated at pH 4 but not at pH 9.6. On gel filtration of mouse serum, a single major peak of activity was obtained with an apparent MW of around 70,000. SER-IA appears to be unrelated to a variety of factors and cytokines which affect M.vphi. function, including colony-stimulating factor-1 (CSF-1). The possible role of SER-IA in regulating the differential expression of SER in vivo is discussed.