Differential cellular immunolocalization of renal tumour necrosis factor‐α production during ischaemia versus endotoxaemia

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Abstract
Both renal ischaemia and endotoxaemia provoke renal dysfunction and cellular injury. Although the clinical manifestation of each insult is similar (global renal dysfunction), ischaemia and endotoxaemia induce different patterns of cellular injury. Tumour necrosis factor‐α (TNF‐α) has been implicated in both types of renal injury; however, it remains unknown whether differential cellular TNF‐α expression accounts for these changes. We hypothesized that renal glomerular cells and tubular cells differentially express TNF‐α in response to ischaemia compared with endotoxaemia. To investigate this hypothesis, male Sprague–Dawley rats were anaesthetized and exposed to various time‐periods of renal ischaemia, with or without reperfusion (sham operation=negative control), or lipopolysaccharide (LPS) 0·5 mg/kg intraperitoneally (i.p.). The kidneys were harvested following renal injury, and rat TNF‐α protein expression was determined (by enzyme‐linked immunosorbent assay), as were TNF‐α bioactivity (by WEHI‐164 cell clone cytotoxicity assay) and TNF‐α cellular localization (by immunohistochemistry). TNF‐α protein expression and TNF‐α bioactivity peaked following 1 hr of ischaemia and 2 hr of reperfusion (48 ± 11 pg/mg of protein, P < 0·05, and 12 ± 0·5 × 10−3 units/mg of protein, P < 0·05, respectively). The concentration of TNF‐α increased to a similar extent following exposure to LPS; however, while TNF‐α production following ischaemia‐reperfusion injury localized predominantly to renal tubular epithelial cells, animals exposed to LPS demonstrated a primarily glomerular distribution of TNF‐α production. Hence, the cellular localization of renal TNF‐α production appears to be injury specific, i.e. renal tubular cells are the primary source of TNF‐α following an ischaemic insult, whereas LPS induces glomerular TNF‐α production. The cellular source of TNF‐α following different insults may have therapeutic implications for targeted inhibition of TNF‐α production.