Time course of changes in cytokine mRNA expression in (a) the submandibular gland (SMG) and (b) the liver of C3H/HeN mice after injection of lipopolysaccharide (LPS). LPS at a concentration of 100 µg/ml of saline was injected intraperitoneally at a dose of 400 µg/kg body weight. Mice injected with saline were regarded as controls. Total RNA (1 µg) isolated from the SMG and liver after injection of LPS at 0, 3, 6, 12 and 24 hr or saline at 0, 6 and 24 hr was reverse-transcribed and PCR-amplified (see Materials and methods). IL, interleukin; TNF, tumour necrosis factor.