Differential Induction of Macrophage GSIB4-Binding Activity

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Abstract
Activated macrophages display a terminal galactopyranosyl group on their membrane surface that binds the lectin Griffonia simplicifolia–IB4 (GSIB4). Using FITC-conjugated GSIB4, we examined the induction and subsequent expression of this corresponding marker on peritoneal macrophages from normal (NMO) and LPS-treated (LPS MO) mice. Although the percentage of fresh LPS MO explants that bound GSIB4 was always higher when compared to the NMO counterparts, marker expression on the latter was readily enhanced by cufturing the cells in vitro either alone or with stimuli. Moreover, we found that an increase in this activity was promoted by either nonspecific phagocytosis of latex beads, or γ-interferon (γ-IFN) treatment. Further investigation showed that a prerequisite sequence of signal delivery to the macrophages was associated with maximal expression of the GSIB4 binding. When γ-IFN treatment preceded latex bead ingestion, maximum GSIB4 binding occurred. Data obtained from using short-term (1 hr) and long-term (24 hr) exposure to latex beads showed that metabolic processing of induction signals was required to enhance the response over time. This yielded better GSIB4-binding activity when responses to these pulses were analyzed in freshly explanted macrophages. The overall results of this study demonstrated that macrophage binding of GSIB4 was differentially associated with stimuli induction. Moreover, select signals in the form of soluble mediators, or the mechanical events characteristic of internalization were capable of eliciting an increase in the percentage of macrophages that were positive for binding GSIB4. Thus, the enhanced affinity for binding this lectin may serve as a useful marker to determine the magnitude of macrophage responsiveness when these cells are examined following their exposure to different stimuli.