Interleukin-12 gene expression in human monocyte-derived macrophages stimulated with Mycobacterium bovis BCG: cytokine regulation and effect of NK cells.

Macrophage-derived interleukin-12 (IL-12) is essential for the activation of a protective immune response against intracellular pathogens. In this study, we examined the regulation of IL-12 mRNA expression by monocyte-derived macrophages (MDM) in response to Mycobacterium bovis BCG stimulation. A reverse transcription-PCR assay detected p40 mRNA of IL-12 at 3 h and showed a peak at 6 to 12 h with a subsequent decline. Semiquantitation of mRNA levels by competitive PCR revealed that pretreatment with gamma interferon (IFN-gamma) amplified the expression approximately 100-fold, while pretreatment with tumor necrosis factor alpha (TNF-alpha) or granulocyte-macrophage colony-stimulating factor augmented this expression about 10-fold. In contrast, pretreatment with IL-10 and IL-4 inhibited IL-12 mRNA expression. These results were further confirmed by measuring the p70 bioactive protein level in each conditioned medium by an enzyme-linked immunosorbent assay. Since IL-12 mRNA expression was weak without cytokine pretreatment and IFN-gamma strongly augmented production, we speculated that IFN-gamma might have a role in BCG stimulation of IL-12 mRNA expression. Unexpectedly, the addition of three different kinds of anti-IFN-gamma antibodies and anti-IFN-gamma receptor antibody and the coaddition of anti-TNF-alpha antibody with anti-IFN-gamma receptor antibody all failed to inhibit IL-12 mRNA expression. However, the MiniMACS method used to remove NK cells from a mononuclear cell suspension inhibited the expression of p40 mRNA but not the expression of mRNA of TNF-alpha or IL-1beta. We concluded that the coexistence of NK cells was essential for the induction of IL-12 in MDM stimulated with BCG rather than through the secretion of IFN-gamma.