Protein changes associated with stages of activation of mouse macrophages for tumor cell killing

Bone marrow-derived mouse macrophages become activated for tumor cell killing by traversing a series of stages. The stages studied here were as follows: unstimulated (exposed to nothing but medium), primed (prepared to become cytolytic), fully activated (primed macrophages exposed to a triggering agent), and postcytolytic (previously activated macrophages that had gradually lost cytolytic activity after the removal of stimuli). Macrophages were labeled with [35S]methionine, lysed, and subjected to 2-D gel electrophoresis and fluorography. The priming agent used was recombinant mouse IFN-gamma, 10 to 20 U/ml. Bacterial lipopolysaccharide (LPS), 0.4 to 1 ng/ml, was used as the triggering agent. A total of 40 major changes was identified in macrophages treated with both agents. Twenty-six of these were seen in macrophages treated with IFN-gamma, and 35 were found in LPS-treated macrophages. Twenty-two of the 40 changes were found in both IFN-gamma- and LPS-treated macrophages. The major reason for this overlap was the autocrine action of IFN-alpha/beta secreted from LPS-treated macrophages. Changes in expression of specific proteins, designated p47b and p71/73, were found to correlate closely with the development and loss of the activated state. With the use of these proteins as markers, phenotypes could be constructed that distinguished unstimulated, LPS-treated, primed, and fully activated macrophages. Postcytolytic macrophages had a phenotype similar to unstimulated macrophages and could be reactivated by reexposure to inducing agents. They also reexpressed the protein markers that were characteristic of fully activated macrophages.