When examining thrombocytic antibodies in serum of patients by the ELISA test concurrently present HLA antibodies were found only in exceptional cases (8), as compared with other tests for the detection of thrombocyte antibodies. One of the possible reasons of this finding could be the mere adsorption of HLA antigens from plasma onto the thrombocyte surface. During the set up of the ELISA test when we work with thrombocytes adhering to the surface of a polystyrene plate and not with a suspension of thrombocytes as in other tests, the spatial arrangement or change of epitopes of HLA antigen could prevent the reaction of HLA antigens with the appropriate antibodies. We tried to test this hypothesis by treating thrombocytes with chloroquine, which is known to remove antigens from the thrombocyte surface, as they are not a firm part of their membrane. Chloroquine actually removed HLA antigens from the thrombocytes as was apparent from: 1. the disappearance of the thrombocyte reactivity with HLA type sera, 2. the inability of thus treated thrombocytes to absorb HLA antibodies from type HLA sera. When resolving the problem of the origin of HLA antigens on thrombocytes we support, based on our results, the view of possible adsorption from plasma, onto the thrombocyte surface. In the discussion the author deals with the possible clinical application of this fact in substitution therapy of refractory patients with thrombocyte concentrates.

Keywords: Blood Platelets /immunology/; Chloroquine /pharmacology/; Fluorescent Antibody Technique; HLA Antigens /analysis/; Humans