Pneumococcus-induced thrombocytopenia in rabbits.

Thrombocytopenia without other hemostatic changes is the most common coagulopathy associated with sepsis. We studied pneumococcus (PNC)-induced hemostatic changes, including thrombocytopenia, in rabbits. Nonviable PNC or saline solution was injected into rabbits preinfused with chromium 51-labeled platelets or iodine 125-fibrinogen. Blood was serially obtained for determination of platelet counts, 51Cr activity or 125I activity, and fibrinogen and fibrin degradation products. Lung, liver, and spleen tissues were counted for 51Cr or 125I activities per gram of wet tissue. PNC-challenged animals displayed profound thrombocytopenia from 0.5 to 48 hours with the mean nadir (-80% relative to the baseline) at 3 hours and a significantly (P less than 0.025) shortened 51Cr-platelet survival of 1.45 +/- 0.71 days vs. 2.72 +/- 1.09 days for saline-injected controls. Circulating fibrinogen level increased, whereas 125I-fibrinogen survival was unchanged (2.6 +/- 0.5 days in PNC-challenged vs. 2.8 +/- 1.0 days in saline-injected). No increased tissue deposition of either 51Cr-labeled platelets or 125I-fibrinogen was found. Rabbits infused with either serum, plasma, or saline solution after each was incubated with PNC all developed significant thrombocytopenia of less than 1 hour duration with maximal mean decreases relative to the baseline of -76% (P less than 0.001), -65% (P less than 0.0005), and -84% (P less than 0.0005), respectively. Inactivation of serum or plasma complement before PNC incubation or heat treatment after PNC incubation in serum or saline solution did not alter the thrombocytopenia. The thrombocytopenia-promoting activity was also trypsin resistant, did not require the presence of serum, plasma, or PNC capsular polysaccharide for its in vitro generation, and had a mol wt of 100,000 to 300,000. Therefore, PNC-induced thrombocytopenia, in the absence of other hemostatic changes, may be explained on the basis of the direct action of a PNC-derived substance(s) on circulating platelets.