Figure 1. Enzyme-linked immunosorbent assay (ELISA) measurement showing the time-dependent secretion of tumour necrosis factor (TNF) into the culture supernatant. Endothelial cells were exposed to selected doses of low linear energy transfer (LET) radiation and harvested at the indicated time points. For the positive control, cells were incubated with 1 µg ml^–1 lipopolysaccharide (LPS) and harvested at 16 h. Sandwich ELISA for TNF was carried out in 0.1 ml of culture supernatant. Cell counts were performed before harvesting, and TNF levels in picograms were normalized to 1 x 10⁶ cells ml^–1.