A previously unrecognized property of the human eosinophil is described; namely, profibrinolysin localization within the eosinophilic granules of bone marrow cells. For this demonstration the fluorescent antibody technic was employed. Highly specific fluorescent antiprofibrinolysin marked all members of the eosinophilic series. As maturation proceeded, the profibrinolysin content increased with the greatest intensity of fluorescence seen in the mature eosinophils. These findings are compatible with the view that the bone marrow eosinophil is the site of profibrinolysin synthesis.

Mature eosinophils in peripheral blood smears consistently stained less intensely. Apparently profibrinolysin is tranported from the marrow and released to the circulation and tissues when needed. These findings may be interpreted as indicating a role of the eosinophil in clot lysis and in maintaining the fluidity of the blood.

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© 1963 by American Society of Hematology, Inc.
1963
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