An Explanation of the Failure of the Direct Antiglobulin Test to Detect Erythrocyte Sensitization in ABO Haemolytic Disease of the Newborn and Observations on Pinocytosis of IgG Anti‐A Antibodies by Infant (Cord) Red Cells

Abstract

Summary. Group A cord cells sensitized with large amounts of IgG anti‐A/B antibodies will give strong antiglobulin test reactions. The failure of the direct antiglobulin test in cases of ABO haemolytic disease is due to the relatively lower level of antibodies sensitizing the cells. The conjugation of ferritin with IgG anti‐A/B globulin gave an electron dense reagent which was used to study the distribution of A sites on adultand infant group A red cells. Similar contagious patterning of A sites was found on both the adult and infant cells’ surface. The levels of conjugated antibodies on the cells of the different bloods were in agreement with the fact that A1 adult cells have more A sites than A2 adult or infant A cells and that A2 adult cells have similar numbers of A sites to A1 infant cells. The distribution of A sites on infant and adult cells shows similar degrees of dispersion. Thus the average distance between A sites must be greater on infant A1 cells than on adult A1 cells. A combination of the small molecular size of IgG antibodies and the relatively greater distances between the A sites of A1 infant cells compared to those of A1 adult cells is proposed to be the cause of the failure of the direct antiglobulin test to give strong reactions with the sensitized cells from ABO HD cases. Pinocytotic activity shown by group A infant cells exposed to IgG anti‐A antibody levels similar to those found in ABO haemolytic disease cases was mainly confined to the more primitive cells containing ribosomes.

Ultrastructural mapping of methyldopa and anti-D IgG erythrocyte antigen receptors.

“…Although there is no overt pattern to the distribution of IgG binding sites, it is evident ( Figs. 1 and 2) that there is a random clumped or "contagious" distribution of sites, similar to that reported for A antigen sites on the red cell (24,25). A variety of distribution patterns would be expected, since the pattern observed depends on the position of the actively moving components at the time the membrane was fixed.…”

“…1 and which has been described by Voak and Williams (24), may be due to technical limitations of the method or may represent true red cell heterogeneity with respect to IgG binding. This variation in staining may be due to differences associated with in vivo red cell age heterogeneity or may in part be due to antigen mobility (13).…”

“…In view of these observations, the present studies were carried out to identify at the ultrastructural level the red cell a-MD IgG receptor sites and to determine if a-MD IgG binds specifically to the red cell D antigen, one of the major antigens in the Rh complex. Immunoferritin conjugates and electron microscopy have been used to stain IgG-sensitized red cells to visualize the receptor site pattern and density of Rh antigens (22,23), the A antigens (22,24,25), and autoantibodies (23). The methods used involved the thin sectioning of the conjugate-stained red cells so that the ferritin-marked IgG sites were visualized in only one plane, i.e., at the periphery of each red cell section.…”

Formation of Intracellular Vesicles in Neonatal and Adult Erythrocytes: Evidence against the Concept of Neonatal Hyposplenism

“…We suggest that the rate of formation of these inclusions is increased in the newborn and overcomes the otherwise normal capacity of the spleen to remove them. Neonatal red blood cells are known to undergo more readily a variety of endocytic processes (1 5), including receptor-mediated endocytosis (10)(11)(12)(13)(14) and drug-induced endocytosis (44). In vivo endocytosis throughout the life span of neonatal erythrocytes has been proposed as an explanation of some of the apparent differences between adult and neonatal red blood cells, including loss of surface membrane, diminished deformability, and higher sphingomyelin content (45).…”

“…Neonatal erythrocytes exhibit an increased propensity to undergo a variety of endocytic phenomena which are unrelated to the function of the spleen (10)(11)(12)(13)(14)(15). We questioned whether the increase in erythrocytic vesicles in neonates was due to enhanced vesicle formation as a consequence of endocytosis and not to diminished splenic clearance.…”