Endotoxin-induced thrombocytopenia in Par4^–/– mice.Par4^–/– males or littermate control males were injected intraperitoneally with 20 mg/kg LPS. Twelve hours later, mice were bled for platelet counts and perfused for immunohistochemistry. (Top left, mean ± SD) Platelet counts in Par4^–/– and littermate controls before and after LPS treatment. (Top right and bottom) Antiplatelet immunostaining of paraffin sections of liver from an LPS-treated Par4^–/– or Par4^+/+ mouse or a saline-treated Par4^+/+ control. Note immunostaining for platelets in microvessels of LPS-treated mice regardless of genotype.