Transforming growth factor‐α expression in peritoneal macrophages elicited from SENCAR and B6C3F1 mice: Responses to lipopolysaccharide and 12‐O‐tetradecanoylphorbol‐13‐acetate

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Abstract
Recent findings in our laboratory indicated that peritoneal macrophages (MPs) elicited from phorbol ester-sensitive SENCAR mice generated significant amounts of superoxide when stimulated by 12-O-tetradecanoylphorbol-13-acetate (TPA) in vitro; negligible responses were observed for MPs derived from relatively resistant B6C3F1 mice. We hypothesized a similar strain-dependent secretion of transforming growth factor-α (TGF-α) by TPA-stimulated MPs. TGF-α secreted by MPs was quantitated by competitive enzyme-linked immunosorbent assay. After 72 h (maximal secretion), for MPs derived from B6C3F1 mice, in vitro exposure to 10 μg/mL lipopolysaccharide (LPS; non-lipid-A-detoxified) resulted in maximal induction (708 pg/mL), in vivo exposure to intraperitoneally (i.p.) administered TPA (2 μg/mouse) alone resulted in a minimal response (32 pg/mL), and prior in vivo exposure to TPA significantly inhibited (more than 90% suppression) the LPS-stimulated MP response in culture (i.e., to 62 pg/mL). Although significant amounts of TGF-α could be detected in both SENCAR-and B6C3F1-derived MPs (i.e., approximately 2–3 ng/5x106 cells), SENCAR MPs did not secrete TGF-α in response to either TPA or LPS. In addition, the use of the semiquantitative reverse transcription-polymerase chain reaction to detect TGF-a-specific mRNA did not support the strain dependency observed for LPS-stimulated TGF-α secretion, i.e., detectable transcripts were observed in MP RNA derived from both strains. In conclusion, although TPA itself demonstrated negligible effects on TGF-α expression in murine MPs, prior in vivo exposure inhibited LPS-stimulated transcriptional activation and intracellular TGF-α production. The negligible TGF-α secretion determined for LPS-stimulated SENCAR-derived MPs suggested the possibility of a strain-specific defect in the posttranslational processing of the proTGF-α molecule.

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