Ultrastructure of the granulocytes of the South American lungfish, Lepidosiren paradoxa: Morphogenesis and comparison to other leucocytes

Ultrastructure and peroxidase cytochemistry of the granulocytes of the lungfish Lepidosiren paradoza were investigated. In peripheral blood and hemopoietic tissue (kidney and spleen) only three granulocytic types were found. After comparison with light microscopic images of Giemsa-stained semithin sections the granulocytes were tentatively designated as eosinophilic I, eosinophilie II, and a basophilic type. The eosinophilc I cell was the most numerous granulocyte and was characterized by granules ranging in diameter from 0.2-1.8 μm. A developmental series was observed, leading from small, peroxidase (PO) positive granules to large ones with PO-negative cores and only peripheral PO-positive reactivity. The central electron-dense cores of the large granules were often eroded. The eosinophlic II cell was less numerous than the eosinophilic I type and had smaller (diameter 0.4-0.9 μm) granules than the eosinophilic I type, some of them elongated and rod like. The basophilic cell was rare and contained large, homogenously dense granules measuring up to 1.2 μm in diameter. Immature stages of the granulocytic types showed vesicular rough endoplasmic reticulum. Nuclear identation and segmentation occurred early in development, in contrast to the relatively late onset of these processes in mamals. Monocytes and macrophages had an irregular or slightly indented nucleus and lacked the specific granules of the granulocytes. Phylogenetic relationships were discussed with special reference to the question of the evolution of only one or possibly of two separate heterophilic/neutrophilic cell lines in fishes. © 1993 Wiley-Liss, Inc.