Monocyte-bound monoclonal antibodies inhibit the Fc gamma RI-mediated phagocytosis of sensitized red cells: the efficiency and mechanism of inhibition are determined by the nature of the antigen

A novel general and efficient technique for dissociating antigen in circulating immune complexes

Circulating immune complexes (CICs) are produced during the immune response. It is more clinically important to establish a general and efficient CICs dissociation technique for the detection of antigens for CICs other than the detection of free antigens in the serum. Polyethylene glycol (PEG) two-precipitation separation and glycine-HCl as a buffer system were employed to develop a general and efficient buffer dissociation technique to separate CICs from serum and dissociate antigens from CICs. The measurement value of new PEG two-precipitation separation technique was higher than traditional PEG precipitation separation technique. There were slight differences in the dissociation conditions of HCV Core-IC, HIV P24-IC, Ins-IC and TG-IC as compared to HBsAg-IC. The detection of antigens in HBsAg-IC, HCV Core-IC, HIV P24-IC, Ins-IC and TG-IC with this technique was superior to that with HCl Dissociation, Trypsin Digestion or Immune Complex Transfer technique. PEG two-precipitation dissociation technique may reduce macromolecular protein and the adhesion of free antigens during the co-precipitation, which increases the efficiency of separation and precipitation of CICs. This technique also avoids the damage of reagents to antigens, assuring the repeatability, reliability and validity. Thus, this technique is application in samples negative or positive for free antigens.

Laboratory assays for predicting the severity of haemolytic disease of the fetus and newborn

Haemolytic disease of the fetus and newborn (HDFN) is characterised by the presence of IgG antibodies in the maternal circulation which cause haemolysis in the fetus by crossing the placenta and sensitising red cells for destruction by macrophages in the fetal spleen. Serological, quantitative and cellular assays have all been developed to predict the severity of HDFN. These assays measure and/or characterise alloantibodies in the maternal circulation. Quantitative assays which accurately measure antibody levels correlate with disease severity better than serological assays which are inherently less precise. Nevertheless, high antibody levels are found in some cases of mild HFDN and relatively low antibody levels are found in some severe cases. This suggests that disease severity is influenced by factors in addition to antibody concentration. These factors remain to be fully elucidated but may include: the subclass and glycosylation of maternal antibodies; the structure, site density, maturational development and tissue distribution of blood group antigens; the efficiency of IgG transport to the fetus; the functional maturity of the fetal spleen; polymorphisms which affect Fc receptor function; and the presence of HLA-related inhibitory antibodies. Cellular assays which are sensitive to factors affecting antibody function have, therefore, been developed in an attempt to improve the prediction of disease severity. Although these assays are cumbersome, there are now sufficient data to suggest that some cellular assays provide clinically useful information to complement serological and quantitative assays.

Fcgamma receptor-mediated immune phagocytosis depends on the class of FcgammaR and on the immunoglobulin-coated target cell

BACKGROUND AND OBJECTIVES

Three human Fcgamma receptors (FcgammaR) are known to mediate immune phagocytosis. A variety of different phagocytic assays have been described, but their comparability is complicated by the use of different effector cells and different antibody-coated target cells. The aim of this study was to determine the influence of these variable components on the FcgammaR-mediated phagocytosis.

MATERIALS AND METHODS

We sensitized human red blood cells (RBC) with polyclonal human anti-D (huaD), or with human monoclonal anti-D of the isotypes IgG1 (huIgG1) or IgG3 (huIgG3). Sheep RBC coated with rabbit immunoglobulin (RBC-RAS) were also used. Monocytes or polymorphonuclear neutrophils (PMN) were incubated with different FcgammaR-specific antibodies or their F(ab')2 fragments to determine the contribution of the different FcgammaRs on these effector cells in the phagocytic process of different antibody-coated target cells.

RESULTS

huaD-RBC and huIgG1-RBC were preferentially ingested via the FcgammaRI on monocytes and, to a minor extent, also by the FcgammaRII. PMN ingested these target cells only after induction of the FcgammaRI by interferon-gamma (IFN-gamma). huIgG3-RBC extensively formed rosettes with monocytes but were seldom ingested. RAS-RBC phagocytosis was induced primarily via the FcgammaRI on monocytes and was mediated by the FcgammaRII on PMN.

CONCLUSION

When performing phagocytosis assays with different effector and target cells, one has to take into account that phagocytosis is mediated by different FcgammaR, making comparability of these assays more difficult.

Receptors involved in the phagocytosis of senescent and diamide-oxidized human RBCs

BACKGROUND

Senescent RBCs bear IgG and C3 opsonins that are three to four times less than required for similar phagocytosis of experimentally opsonized RBCs.

STUDY DESIGN AND METHODS

Studies were performed to determine the phagocyte receptors involved in phagocytosis in vitro. The effect of clustering of opsonins and oxidative damage in the sequestration of RBCs was studied by exposing RBCs to BS3 (bis[sulfosuccinimidyl]-suberate) and diamide (azodicarboxylic acid bis[dimethyl-amide]).

RESULTS

Sequestration of senescent RBCs was inhibited by the treatment of lymphokine-activated monocytes with N-acetyl-D-galactoseamine (GalNAc), arginine-glycine-aspartic acid (RGD), or antibodies to CR3, FcgammaRI, FcgammaRII, leukocyte response integrin (LRI), and integrin-associated protein (IAP). Exposure to BS3 alone did not enhance phagocytosis. The addition of serum resulted in opsonin binding. The level of opsonization required for sequestration was higher than on senescent RBCs and was only marginally inhibited by blocking CR3, FcgammaRI and FcgammaRII. Diamide treatment alone did not lead to sequestration. Diamide-treated RBCs exposed to serum bound opsonin much as did senescent RBCs, and sequestration was inhibited by GalNAc, RGD, and antibodies to CR3, FcgammaRI, FcgammaRII, LRI, and IAP.

CONCLUSION

Membrane alterations resulting in the binding of opsonins and the sequestration of senescent RBCs may be similar to those that occur on diamide-oxidized RBCs. They suggest the need for cooperative events among oxidation, clustering and cross-linking, and serum opsonization.

A comparison of in vitro tests for predicting the severity of haemolytic disease of the fetus and newborn

Haemolytic disease of the newborn (HDN) is characterized by the presence of IgG antibodies in the maternal circulation which cause haemolysis in the fetus by crossing the placenta and sensitizing red cells for destruction by macrophages in the fetal spleen. Numerous serological, quantitative and cellular assays have been developed to predict the severity of HDN. These assays all measure and/or characterize alloantibodies in the maternal circulation. Quantitative assays which accurately measure antibody levels correlate with disease severity better than serological assays which are inherently less precise. Nevertheless, high antibody levels are found in some cases of mild HDN and relatively low antibody levels are found in some severe cases. This suggests that disease severity is influenced by factors in addition to antibody concentration. These factors remain to be fully elucidated but may include the subclass and glycosylation of maternal antibodies, the structure, site density, maturational development and tissue distribution of blood group antigens, the efficiency of IgG transport to the fetus, the functional maturity of the fetal spleen, polymorphisms which affect Fc receptor function, and the presence of HLA-related inhibitory antibodies. Cellular assays which are sensitive to factors affecting antibody function have therefore been developed in an attempt to improve the prediction of disease severity. Although these assays are cumbersome, there are now sufficient data to suggest that some cellular assays, when used as part of a structured approach to diagnostic testing, may provide clinically-useful information to complement serological and quantitative assays.