Murine gamma interferon activates the release of a macrophage-derived Ia-inducing factor that transfers Ia inductive capacity.

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Abstract
When the murine macrophage tumor cell line P-388D1 is incubated for 48-72 h with either concanavalin A[Con A]-stimulated rat spleen cell supernatant or cloned murine immune interferon (IFN-.gamma.), the cultured cells release a cell-free factor activity that in turn induces the cell surface expression of Ia antigen on the murine monocyte cell line WEHI-3. This IFN-.gamma.-stimulated, Ia-inducing activity cannot be blocked with an anti-IFN-.gamma. heteroantiserum that does block the induction of Ia expression on WEHI-3 by both cloned murine IFN-.gamma. and rat Con A supernatant. The Ia-inducing factor (IaIF) generated from P-388D1 after stimulation by IFN-.gamma. does not demonstrate any antiviral activity. The P-388D1-derived IaIF is not shed plasma membrane Ia glycoprotein molecules, as demonstrated by the inability of the active component to bind specifically to an anti-I-Ad affinity column or to a protein A column after the active supernatant is first treated with an excess of anti-I-E/Cd,k monoclonal antibody.