Conditions required for expression of membrane IL 1 on B cells

We have reported that macrophages bear a mitogenic activity for T cells in their plasma membrane that we have termed 'membrane-interleukin 1' (membrane IL 1). Membrane IL 1 was studied by using either paraformaldehyde-fixed macrophages or isolated macrophage membranes. The reason for ascribing this membrane activity to IL 1 was based on the observation that macrophage membranes stimulated proliferation of thymocytes and an IL 1-dependent T cell line but IL 2-dependent T cells, and this activity was inhibited by a polyclonal goat anti-IL 1 antibody. Additional biochemical studies need to be done to unequivocally establish the interrelationships between the soluble IL 1 and the membrane form. Nevertheless, two important features of the membrane IL 1 were noteworthy: first, it was essential that Ia-bearing, fixed macrophages express it to activate antigen-specific T cell lines, and second, its expression could be dissociated from the secretion of IL 1. Because B cells are known to function as antigen-presenting cells, we investigated whether these cells express membrane IL 1.