Erythroblast

Erythroblast, a cell from which a red blood cell-erythrocyte is formed. In an adult human under normal conditions, E. are found only in the bone marrow and are completely absent in circulating blood; in animals, individual E. may appear in the blood even in a normal state. Ontogenetically, two sharply distinct groups of E. are separated: giant E. of the early embryonic period - megaloblasts [see separate table (pp. 503-504), fig. 6] and normal, resp. macroblasts [see separate table (pp. 503-504), fig. 7 and 8] at later stages of development (see Hematopoiesis). In human pathology, the megaloblastic type of hematopoiesis in its pure form, as occurs in the embryo, is never encountered; megaloblasts appear only together with macro- and normoblasts. By the structure of the nucleus (delicate reticular, poor in basichromatin) and by the nature of the protoplasm (distinguished by hyperchromia, intense staining with Hb, often with marked polychromasia), pathological megaloblasts [see separate table (pp. 503-504), fig. 9] correspond to embryonic megaloblasts, and most authors interpret their development as a return to the embryonic type of hematopoiesis. Maximov, however, asserts that the megaloblasts encountered in pernicious anemia have nothing in common with the megaloblasts of the first embryonic generation. Naegeli considers megaloblasts absolutely characteristic of pernicious anemia and sees in them the manifestation of a constitutional anomaly in the laying down of bone marrow with the preservation of the hematopoietic potency of early embryonic tissue. Other authors do not recognize such specificity in the megaloblast and explain its appearance as a violation of hemoglobin metabolism and the associated change in the functional irritation of erythropoietic tissue, as is observed, for example, in nutritional anemias in children of the Jaksch type. In the protoplasm of E., both of megaloblastic type and of macro- and normoblastic type, mitochondria, which are characteristically stained with Janus green, and granules, which are stained with neutral red, are found. With supravital staining, these structures are revealed as substantia granulo-filamentosa. Along with the nucleus, in some E., extruded paranuclei [see separate table (pp. 503-504), fig. 6] and Jolly-Howell nuclear bodies [see separate table (pp. 503-504), fig. 7 and 9] are found. The nuclei of megaloblasts subsequently sharply shrink, becoming pycnotic. The nuclei of normoblasts also become pycnotic, the chromatin of the nucleus is often arranged in the form of a wheel; in addition, fragmentation of the nucleus, which takes the form of a trefoil, etc., is often observed. With enhanced regeneration, young E., or so-called proerythroblasts [see separate table (pp. 503-504), fig. 8], form in the bone marrow segmentally located strands; foci of mature normoblasts usually appear as irregularly shaped areas. Into the circulating blood, E. enter in large quantities during the so-called blood crises of Noorden in various types of anemias, then in the period of regeneration in hemolytic processes caused by exogenous or endogenous toxic substances, in metastases of a tumor to the bone marrow; enormous quantities of E. are found in the so-called erythroblastoses (see Myeloses). In newborns with icterus gravis, the blood is often flooded with E., as in certain forms of congenital syphilis. In the so-called erythroblastic anemia (erythroblastic anemia)-a hereditary anemia in children-the number of E. can reach large figures, as in Lederer anemia. In small quantities, E. are found in various forms of anemias, especially in childhood, as well as in polycythemia and in leukemia. In all these cases, the appearance of E. in the circulating blood indicates a violation of the mechanism of hematopoiesis in the sense of the entry into the blood of elements that have not completed their normal metamorphosis in the bone marrow. In the protoplasm of normoblasts, basophilic granularity in the form of basophilic stippling of varying size and intensity is often found in pathological regeneration [see separate table (pp. 503-504), fig. 7]. In animals poisoned with lead, all stages of its development can easily be observed in polychromatophilic E. from the basophilic stroma of the protoplasm. Erythroconts (rods found in erythrocytes with supravital staining and with intense staining by Giemsa), described by Schilling mainly in pernicious anemia and observed in various hemolytic anemias, have not yet been noted in erythroblasts by anyone. Borst and Konigsdorfer, using a luminescence microscope, found in the bone marrow in congenital uroporphyrin "fluorescing E. containing porphyrins. At present, fluorescing E. are found in various forms of anemias. Fluorescing erythrocytes or fluorescites are found by this method of investigation in normal amounts up to 1‰, and in anemias in significantly increased amounts (Keller, Seggel). Nucleus-containing erythrocytes of cold-blooded animals, when investigated in vivo by electroanalytical means with the help of vital staining with tripanflavin and fluorescein, proved to be electropositive with a 10-millivolt negative charge of the shell. Lit.: Keller P., Elektroanalyse van Blutkörperchen, Fol. haemat., B. LII, H. 3, 1934; Keller C. u. Seggel K., Cber das Vorkommen fluorescierender Erythrocyten, ibid., B. LII, H. 3, 1934; Koch L. a. Shapiro B., Erythroblastic anemia, Amer. journ. o{ dis. of child., v. XLIV, 1938.