Receptor Cross-Talk: Protein Kinase C Dependent Down-Modulation of the Colony-Stimulating Factor-1 Receptor upon Activation with Interferon-γ/Lipopolysaccharide

Induction of macrophage cytocidal activity is a multistep process requiring both a priming signal, such as interferon-gamma (IFN-γ) or interleukin-4, and a triggering signal, such as lipopolysaccharide (LPS), lipophilic muramyl tripeptide, or pertussis toxin. The binding of IFN-γ to its cell surface receptor primes the cells to respond to a triggering signal, LPS. Upon interaction with this triggering signal, primed macrophages become fully activated and acquire the ability to kill neoplastic cells and micro-organisms [1–3]. Both priming and triggering agents have been shown to synergistically inhibit macrophage growth, possibly reflecting the existence of a mechanism controlling the proliferation of activated cells [4].