Platelet autoantibodies in septicaemia

Thirty-three patients, 16 of whom had a platelet count below 100 X 10(9)/l, were studied for the presence of platelet antibodies using the platelet suspension immunofluorescence test (PSIFT). In the acute phase platelet-bound immunoglobulins (PBIg) were found in 62% of the thrombocytopenic patients, but also in 65% of the patients with a normal platelet count. Fourteen patients were re-examined after successful treatment of their infection. At that time all had a normal platelet count, yet PBIg were found in 71%. In all but four patients the PBIg could be eluted with ether and were shown to bind to normal platelets but not to Glanzmann type I platelets in 11 of 12 patients tested, indicating the platelet-specific autoantibody nature of the PBIg. Platelet autoantibodies were also demonstrated in the sera: in 38% in the acute phase and in 43% after treatment. In those patients in whom this could be tested the antibodies appeared to be strictly or partially EDTA-dependent. It is postulated that the antibodies are mainly directed against cryptantigens, exposed in vivo only on platelets damaged by the septicaemia and in vitro in the presence of EDTA. This would also explain the lack of relationship between the platelet count and the serological findings.