The direct immunoperoxidase technique was employed to show the localization of transferrin in immature human erythroid cells. The present method is interesting in that use was made of a small marker (HRP-Fab’ complex) and in that the endogenous peroxidase was blocked under a controlled condition – this ensured good structural preservation allowing electron-microscopic examination. Cytoplasmic transferrin was found not only in the micropinocytotic vesicles but also within the mitochondrial membrane. Similar findings were made in all the immature erythroid cells examined, each of which was in a different erythropoietic condition. Thus, it may be concluded that the present study provides morphological evidence for the endocytotic iron transport to the mitochondria.

No abstract

We tested the hypothesis that the secretion of IgA into intestinal fluids is modulated by increases in epithelial cell cyclic AMP. Cholera enterotoxin instilled into intestinal loops of rabbits did not induce IgA secretion, even though an appropriate fluid response was obtained. The findings, therefore, do not support the hypothesis.