Immune elimination of aging platelets by autologous monocytes: role of membrane-specific autoantibody

Binding of serum autoantibodies to sialidase-treated tracheal epithelial cells. Determination of autoantibodies isotypes in normal and influenza virus infected guinea pig sera

Cultured epithelial cells isolated from guinea pig trachea were treated with Vibrio cholerae sialidase. The treatment was not cytotoxic and resulted in membrane desialylation as assessed by measurement of sialic acids released, along with an increased fixation of the galactose-specific lectin peanut agglutinin. After incubation in serum from normal guinea pigs, membrane-bound immunoglobulins were detected using peroxidase-labelled antibodies. Sialidase-treated cells bound significantly more IgM than controls (P < 0.0005), whereas binding of IgG was not significantly different between treated and untreated cells (0.1 < P < 0.375); IgA were never detected. In influenza-infected guinea-pigs, as assessed by reactivity with peanut agglutinin, the tracheal and lung epithelium, as well as alveolar cells were hyposialylated. In these animals, the level of serum IgG autoantibodies capable to bind sialidase treated cultured cells increased, while the level of IgM autoantibodies did not change. These autoantibodies may participate in cellular dysfunctions and modified bronchoreactivity that occur during infection of the respiratory tract by sialidase-producing microorganisms, either through activation of the complement system, or subsequently to their reaction with cells expressing membrane complement and/or Fc receptors.

Molecular mapping of human band 3 aging antigenic sites and active amino acids using synthetic peptides

An aging antigen, senescent cell antigen appears on old cells and marks them for death by initiating the binding of IgG autoantibody and subsequent removal by phagocytes. This antigen is derived from the major anion transport protein, protein band 3, that is involved in respiration and acid base balance. We use synthetic peptides from the transmembrane, anion transport segment of band 3 to "walk" band 3 to identify potential aging antigenic sites. A competitive inhibition assay with affinity purified IgG autoantibody from senescent red cells was used. Results indicate that: aging antigenic sites reside on human band 3 residues 538-554, 593-601, and 812-830; and that the smallest residues which act as aging antigenic sites are 593-601 and 813-818. The contribution of lysine and/or arginine to antigenicity is examined by synthesizing peptide analogs in which glycines or arginines are substituted for lysines or arginines. Substitution of neutral glycine for the positively charged amino acids arginine or lysine or both arginine and lysine did not result in a significant difference in antigenicity between the analog and the native band 3 peptide. Substitution of the positively charged arginine for the positively charged lysine resulted in a significant reduction in antigenicity. The chicken sequence of band 3 peptides 538-554 and 812-827 differs from that of the human peptides at several sites. Antigenicity of these chicken "analogs" were tested and compared to the human peptides. The data suggest that the three-dimensional configuration of band 3 segments plays a dominant role in defining the antigenic determinants reactive with senescent cell IgG autoantibodies.

Hypothesis: synthetic aging antigen can be used to manipulate cellular lifespan

Physiologic removal of old and damaged erythrocytes, platelets, and other terminally differentiated cells is initiated by the appearance of an aging antigen that marks them for death by initiating the binding of IgG autoantibody and subsequent removal by phagocytes. We have developed a synthetic aging antigen peptide that blocks binding of IgG to senescent cells in vitro. We hypothesize that the synthetic antigen can be used to prevent cell destruction in diseases such as autoimmune hemolytic anemias and idiopathic thrombocytopenia purpura, and that the antigen itself can be used to manipulate cellular lifespan in vivo.

Characterization of autoantibodies to vasoactive intestinal peptide in asthma

Vasoactive intestinal peptide (VIP) is a potent relaxant of the airway smooth muscle. In this study, VIP-binding autoantibodies were observed in the plasma of 18% asthma patients and 16% healthy subjects. Immunoprecipitation studies and chromatography on DEAE-cellulose and immobilized protein G indicated that the plasma VIP-binding activity was largely due to IgG antibodies. Saturation analysis of VIP binding by the plasmas suggested the presence of one or two classes of autoantibodies, distinguished by their apparent equilibrium affinity constants (Ka). The autoantibodies from asthma patients exhibited a larger VIP-binding affinity compared to those from healthy subjects (Ka 7.8 x 10(9) M-1 and 0.13 x 10(9) M-1, respectively; P less than 0.005). The antibodies were specific for VIP, judged by their poor reaction with peptides bearing partial sequence homology with VIP (peptide histidine isoleucine, growth hormone releasing factor and secretin). IgG prepared from the plasma of an antibody-positive asthma patient inhibited the saturable binding of 125I-VIP by receptors in guinea pig lung membranes (by 39-59%; P less than 0.001). These observations are consistent with a role for the VIP autoantibodies in the airway hyperresponsiveness of asthma.

Human autoantibody to vasoactive intestinal peptide: increased incidence in muscular exercise

Specific autoantibodies to vasoactive intestinal peptide were present in plasma from 29.6% healthy human subjects who habitually performed muscular exercise, compared to 2.3% healthy subjects who did not. Saturation analysis of VIP binding by the plasmas suggested the presence of 1 and 2 classes of autoantibodies in 5 and 3 high exercise subjects, respectively, distinguished by their equilibrium affinity constants (Ka). The mean Ka values for the high and low affinity autoantibody classes were, respectively, 1.3 x 10(8) M-1 and 0.8 x 10(7) M-1. These values are lower than the Ka range reported previously for tissue VIP receptors (G. Rosselin. Peptides 7, Suppl. 1, 89, 1986) but are larger than the inverse Michaelis constant (1/Km) for VIP-degrading proteases (T.N. Keltz, E. Straus, R.S. Yalow. Biochem. Biophys. Res. Commun. 92, 669, 1980). The autoantibodies may not interfere with VIP-receptor binding but are potential inhibitors of the proteolytic inactivation of VIP.

Factor XIII: a marker of mono- and megakaryocytopoiesis

Previous studies have shown that human platelets, megakaryocytes and peripheral blood monocytes contain the subunit a of plasma factor XIII (FXIII) which plays a key role in fibrin stabilization. To study the expression of FXIII subunit a during differentiation of the mono- and megakaryocytic cell lines, bone marrow smears were examined by immunomorphological methods. In addition to megakaryocytes, FXIII was detected in a large number of cells by a highly sensitive immunoperoxidase staining. Characterization of these cells was carried out by double immunofluorescent labelling in which the detection of FXIII subunit a was combined by the labelling of either Leu M3 monocyte/macrophage surface antigen or platelet factor 4 (PF4) a marker for megakaryocytic cells. On the course of differentiation from early precursors to mature megakaryocytes all phenotypic form of the megakaryocytic cell line expressed FXIII subunit a though there were considerable changes in its subcellular distribution pattern. Leu M3 positive cells of monocytopoiesis, i.e. monocytes and promonocytes and in all probability monoblasts as well, were also labelled for FXIII. On this basis FXIII subunit a could be considered as a common marker of megakaryo- and monocytopoiesis and its immunomorphological detection might provide a useful diagnostic tool for identifying normal and perhaps also malignant differentiation forms of these cell lines.

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Oxidation as a possible mechanism of cellular aging: vitamin E deficiency causes premature aging and IgG binding to erythrocytes

Senescent-cell antigen is a "neo-antigen" that appears on the surface of senescent cells and initiates IgG binding and cellular removal. As an approach to evaluating oxidation as a possible mechanism for generation of senescent-cell antigen, we studied erythrocytes from vitamin E-deficient rats. Vitamin E is localized primarily in cellular membranes. Its major role is the termination of free-radical chain reactions propagated by the polyunsaturated fatty acids of membrane propagated by the polyunsaturated fatty acids of membrane phospholipids. Results of our studies indicate that erythrocytes of all ages from vitamin E-deficient rats behave like old erythrocytes from normal rats, as determined by their susceptibility to phagocytosis, IgG binding, anion transport ability, and glyceraldehyde-3-phosphate dehydrogenase activity. Increased breakdown products of band 3 were observed with immunoblotting in membranes of erythrocytes from vitamin E-deficient rats. Breakdown products of band 3 are known to increase as cells age in normal individuals. The data suggest that oxidation may be a possible mechanism for erythrocyte aging and generation of senescent-cell antigen in vivo.

Autoantibody to vasoactive intestinal peptide in human circulation

In a radioassay for Vasoactive Intestinal Peptide (VIP)-binding, eight out of 33 plasma samples from healthy human subjects exhibited specific binding ranging from 2.6% to 46.7% of total [125 I]VIP. This binding was competitively displaced by unlabeled VIP. The structurally homologous peptides, Peptide Histidine Isoleucine (PHI) and secretin, were, respectively, 72-fold and 413-fold less potent than VIP in displacing bound [125 I]VIP, whereas the unrelated peptides, neurotensin, eledoisin, bombesin and metenkephalin, were without effect on the binding. The antibody nature of the VIP-binding factor was suggested by its precipitation with ammonium sulfate, attenuation after absorption with Staphylococcus aureus preparations, precipitation with antisera against human IgG and IgM, and coelution with standard IgG and IgM on anion-exchange and high-performance gel-filtration columns. Pepsin treatment of purified IgG fraction yielded a VIP-binding species with apparent molecular weight of 108 +/- 13 kDa that was precipitated by antiserum against the F(ab)2 fragment of the IgG molecule. These results demonstrate the existence in some human plasmas of an autoantibody that binds VIP.

Factor XIII of blood coagulation in human monocytes

The presence of Factor XIII subunit a was demonstrated in human monocytes by immunoperoxidase staining using specific antisera against Factor XIII and its subunits. This finding was verified by immunobiochemical techniques, as well. In an immunoblotting system after SDS polyacrylamide gel electrophoresis of denatured monocyte homogenate a protein band comigrating with Factor XIII subunit a showed positive reaction with antibodies against this subunit or whole Factor XIII. In contrast, no subunit b of Factor XIII could be detected by either of these methods in monocytes. Activity measurements were carried out by the dansylcadaverine incorporation assay in the absence and presence of anti-Factor XIII antibody with and without thrombin activation. The expression of transglutaminase activity required thrombin and was completely abolished in presence of anti- Factor XIII antibody, which clearly indicate that practically all the transglutaminase activity measured in monocytes comes from Factor XIII. Factor XIII of monocytes and macrophages might have a role in formation of focal fibrin thrombi as well as in organization of stable, fibrinolysis resistant fibrin clot at the site of inflammation or around tumor cells.

Antibodies against ss-DNA in persons of various age

Antibodies against denatured, single-stranded deoxyribonucleic acid were measured in the sera of children, young adults and old persons by means of a solid phase enzyme-linked immunosorbent assay using a peroxidase-labelled second antibody. Considerable amounts of anti-deoxyribonucleic acid antibodies were found in subjects in all the age groups studied. Mean serum activity in children and old persons was two times as high as that in young adults. Close correlation was observed in old age between the level of antibodies against single-stranded deoxyribonucleic acid and disorders of lipid metabolism, namely hypertriglyceridemia and hypercholesterolemia. Based on their finding that substantial quantities of antibodies of the above type appear to be present in healthy humans at different stages of ontogenesis, the authors suggest these autoantibodies may play, in addition to pathological, some physiological role.