Differential Stimulation Requirements for IL-12 Production Among Clones of Macrophage Hybridomas

We have previously established cloned macrophage hybridomas by somatic cell fusion of the macrophage tumor P388D₁ of DBA/2 (H-2^d) origin with splenic adherent cells of CKB mice (H-2^k). Several cloned lines displayed the serologic and functional characteristics of macrophages. In this study, we evaluated the ability of these hybridomas to produce IL-12 after combined stimulation with IFN-γ and lipopolysaccharide (LPS). The patterns of IL-12 production by these cloned macrophages fell into three groups. The first group produced IL-12 on stimulation with LPS in combination with IFN-γ pretreatment, the second group produced IL-12 on stimulation with LPS regardless of the pretreatment with IFN-γ, and the third group did not produce IL-12 at all on stimulation with IFN-γ and LPS. None of the macrophage clones tested produced IL-12 constitutively. The results correlated well with IL-12 p40 mRNA expression in those macrophages as detected by RT-PCR. These results suggest the differential stimulation requirements for IL-12 production among macrophages at a clonal level.