Erythrophagocytosis in the caprine hemal node

Caprine hemal nodes were studied by transmission electron microscopy after glutaraldehyde fixation and epoxy resin embedding. Hemal node macrophages were observed to be engaged in erythrophagocytosis. In the early stages of endocytosis, intact erythrocytes were contained in some of the heterophagic vacuoles of macrophages. Later, granular, electron-dense material appeared on erythrocytes, presumably as a result of lysosomal degradation of their matrices. Subsequently, the matrix fragmented and probably formed 'myelin-like figures' and residual bodies that dominated the macrophage cytoplasm. In addition, images of sinusoidal endothelium, reticular cells, lymphocytes and, rarely, eosinophils were observed that depicted structures resembling various stages of lysosomal digestion of erythrocyte matrix noted in macrophages. Our study provides evidence to support the fact that effete erythrocytes are filtered, besides known organs, also in caprine hemal nodes. The morphology and location of hemal nodes suggest that the organ can be an efficient blood filter.