The spreading of blood platelets after adhesion was first observed by Eberth et al. (1885) and has been studied since by many investigators. The underlying mechanisms, however, are not known in many respects and there has been no report so far of its electron microscopic observation.
PURPOSE: For making observation of the mode of normal platelet adhesion and spreading by scanning electron microscopy as well as to investigate morphological changes of spreading platelets in elected hematologic disorders.
SUBJECTS: The mechanism of platelet spreading was investigated with specimens from healthy male adults, followed by comparison of the spreading of plateles from patients with C. M. L. or I. T. P.
PROCEDURE: Platelets were allowed to spread on plastic plates by the method of Breddin and fixed after intervals of 5, 15 or 30 minutes for microscopic observation. Those from patients were fixed after 30 minutes of spreading. For electron microscopy, specimens were fixed with 1% glutaraldehyde and, after postfixation in 1% OsO4, they were dehydrated, dried and covered by the vacuum evaporation of carbon and metal.
RESULTS: Mode of spreading—At 5 minutes of spread each platelet was found to have sent out one or two pseudopodia. When 15 minutes had elapsed the pseudopodia were found increasing in number and elongated to shape up a dendritic form. At 30 minutes, the platelet was spread to assume a discoid shape with the peripheral transparent hyalomere and the central portion consisting of a gel-like material. A series of scanning electron micrographs shows that, generally speaking, the platelet sends out pseudopodia which thereafter increase in number and extend to form dendroid structures with a subsequent formation of the hyalomere just like a membrane spreading around neighboring pseudopodia; the platelet thereby gradually spreads into an ellipsoid shape. An occasional platelet shows the formation of a clear zone by a sol-like outflow around the pseudopodia, followed by its confluence with the substance from the central portion to eventually make the platelet discoid. It was also noted that a platelet had a peripheral clear zone formed around it at as early as the initial stage of adhesion and thereafter appeared to continue spreading in all directions; it remains yet to be determined whether or not this represents the consequences of a rapid progress in platelet spreading in either of the foregoing two fashions. Platelets from patients—Most platelets from CML patients were found asteroid with incompletely spread peripheral dendroid structures. In ITP, platelets were ellipsoid and displayed remarkably active spreading; the central portion consisted of a gel-like substance with an irregularly uneven surface and with trabeculations around it.
CONCLUDION: Blood platelets were observed to spread in three different modes, and this finding would be of significance as an aid to elucidation of the process of platelet adhesion. The observation also disclosed a remarkably striking difference in the morphology of platelet spreading between CML and ITP, suggesting likely abnormalities of platelet function in these conditions.
