Comparison of Normal and Thrombasthenic Human Blood Platelets

The ultrastructure of normal human blood platelets in the resting state has been described in detail. Platelets recovered from citrated plasma of a patient with Glanzmann's thrombopathy or thrombasthenia have a similar appearance (Fig. 1). These anucleate cells are usually disc shaped and hence are round or oval, depending upon the plane of sectioning. They have randomly dispersed cytoplasmic organelles and microtubules which are typically arranged in a marginal band. Platelet responses to several agglutinating agents and the relation of platelets to fibrin during clotting have been reported. On exposure to thrombin, to ADP, or to collagen, normal and thrombasthenic platelets undergo similar early morphologic changes. Pseudopods form and organelles move toward platelet centers, with microtubules being outermost of the closely packed, centrally apposed organelles. A peripheral rim of cytoplasm is essentially organelle-free except for an occasional mitochondrion or vacuole and except for microtubules which sometimes extend outward into pseudopods. Following these early, preagglutination changes normal platelets agglutinate in response to each of the 3 agglutinating agents, whether in autologous plasma or in salt solution after repeated washings. Thrombasthenic platelets in autologous plasma fail to agglutinate in response to thrombin or to ADP and agglutinate only minimally on exposure to finely divided collagen.