Effects of endotoxin-treatment on inflammatory cell infiltrates in murine Meth A sarcoma

The effect of intravenously injected endotoxin on inflammatory cells within solid Meth A tumours was studied and central hyperaemia, necrosis and early collapse were observed macroscopically at 4, 24 and 48 h, respectively. The effects were studied in semithin sections and cytocentrifuge preparations of the tumours. The inflammatory cell reaction evoked by the tumours in untreated animals was relatively slight. It was located predominantly around the lateral margins of the tumours and only a few inflammatory cells were found inside the tumour. Prominent effects of endotoxin included a transient increase of mononuclear inflammatory cells in the centre of the tumour by 4 h and a reduction of the influx of lymphocytes, observed in and around the margin of control tumours, by 48 h. Mast cells formed an important part of the inflammatory cell infiltrate, but no distinct changes in number and appearance were observed with time or following treatment. Total host cell numbers within tumours did not increase significantly upon endotoxin-treatment. Results suggest that a direct cytotoxic action of host cells cannot account for the extensive tumour damage observed. Rather, endotoxin-induced regression seems to be related to decreased lymphocyte numbers.