Differential activation of resident macrophage subsets with two sources of lymphokine preparations

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Abstract
Resident murine macrophages were separated into subsets by Percoll density gradient centrifugation before treatment with lipopolysaccharide-stimulated lymphocytes or different lymphokine preparations. The lymphokines used were culture supernatants from lymphocytes obtained from lipopolysaccharide-injected mice or from purified protein derivative-treated lymphocytes from mice bearing an active BCG infection. The macrophage subsets were activated by the stimulated lymphocytes or lymphokine preparations to express C3b receptor-mediated ingestion or to inhibit the intracellular replication of Toxoplasma gondii or both. The results showed that the macrophage subsets were heterogeneous with respect to ingestion and T. gondii inhibition when activated with lipopolysaccharide-stimulated lymphocytes or lipopolysaccharide-derived lymphokines but were all homogeneous when activated with lymphokines from purified protein derivative-stimulated lymphocytes. When the macrophage subsets were allowed to remain in vitro for various times before lymphokine treatment, the relative pattern of subset activation changed when treated with lipopolysaccharide-derived lymphokines. In contrast, the macrophage subsets remained equally activated throughout the in vitro period when treated with the lymphokines from purified protein derivative-stimulated lymphocytes. The results suggested that functional macrophage heterogeneity depends not only on the nature of the activating signal but also on a state of receptivity of that signal by the macrophage population.