Differential reactivity of structural components of eosinophil leucocyte granules as revealed by ethanolic phosphotungstic acid

After glutaraldehyde fixation and ethanolic phosphotungstic acid (E-PTA) treatment before embedding, thin sections of rat bone marrow and large intestine showed a characteristic pattern of electron opacity in eosinophil leucocyte granules. In both mature eosinophils and precursor cells, the matrix appeared highly contrasted while the crystalline core revealed no electron density. Additional treatment of sections with uranyl acetate did not modify the contrasting pattern of eosinophil granules. The absence of electron dense reaction in the crystalline core after E-PTA treatment seems to originate from removal of core components. The selective reactivity of the matrix toward E-PTA could be a valuable ultrastructural marker for studies on the differentiation of specific granules along the maturation of eosinophil leucocytes.