The role of membrane gangliosides in murine alveolar macrophage-mediated suppression of the immune response

Surface expression of Forssman glycosphingolipid antigen on murine bone marrow-derived macrophages is subject to both temporal and population-specific regulation and is modulated by IL-4 and IL-6

The Forssman glycolipid antigen (Fo) has been shown to be a differentiation marker for mouse macrophages both in vivo and in vitro. In order to determine whether or not there is a relationship between stage of differentiation and Fo expression, we have analyzed the kinetics of Fo expression during the growth of cultured mouse bone marrow-derived macrophages (BMDM). BMDM were grown in serum free medium to avoid the possible influence of undefined serum factors. In this medium they could be maintained over a period of up to 20 days with cell yields comparable to those obtained with serum-supplemented media. Fo antigen was assayed with a specific antibody using both a whole cell ELISA and immunocytochemical staining of cells grown on slides. With increasing age in culture, BMDM showed a gradual quantitative increase in Fo expression and parallel increase in the Fo+ BMDM fraction from about 10% Fo+ cells on the 10th day of culture to a maximum of 50%-60% Fo+ cells between the 17th and 19th days. The temporal control over the development of the Fo+ cell fraction was intrinsic to BMDM maturation but was specific for Fo. During the same time period expression of MHC class II (Ia) remained consistently low, whereas expression of both Mac-1 (C3bR) and the macrophage-specific marker ER-BMDM-1 was always high. The interleukins IL-4 and especially IL-6 induced a premature expression of Fo at earlier stages of BMDM culture, but neither could promote further Fo expression once the intrinsically occurring maximum had been reached. No evidence in support of an autocrine regulation of Fo expression by IL-6 could be obtained, nor could a connection between cell cycle status and Fo expression be established. These data provide further evidence that Fo is a temporally regulated differentiation marker for a mouse macrophage subpopulation and for modulation of its expression by lymphokines.