The present studies determined the effects of extracellular pH (pHo) on the production of tumour necrosis factor-α (TNF-α) in the macrophage-like cell lines RAW 246.7 and J774 A.1. The cells were activated with lipopolysaccharide (LPS) at pHo 5.5, 6.5 or 7.4. TNF-α gene transcription was monitored by Northern blot analysis. Synthesis of the cytokine was monitored by ELISA measurements of the TNF-α content of cell-conditioned media (extracellularly released TNF-α) and cell lysates (cytosolic TNF-α). The magnitude of the TNF-α response differed markedly between the two cell lines. RAW cells were more responsive to LPS than were J774 cells. However, the effects of pHo on TNF-α production were similar in the two cell lines. TNF-α gene transcription was insensitive to experimental pHo. The pHo had no effect on the abundance of TNF-α mRNA at 2, 4 or 18 h. Nonetheless, synthesis of TNF-α was affected significantly by pHo. The TNF-α contents of cell-conditioned medium and cell lysate at 18 h were reduced progressively at lower pHo values. The data indicate that pHo alters TNF-α production in RAW and J774 cells at a post-transcriptional level. These findings suggest that pHo influences the phenotypic responses of macrophages to activating stimuli and modifies the role that macrophages play in inflammatory and immune actions.

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