Incidence of anti-mouse antibodies in thrombocytopenic patients with autoimmune disorders

Idiopathic thrombotycopenic purpura (ITP) is an autoimmune disorder in which circulating autoantibodies react with target antigens on the platelet membrane. In order to identify the autoimmune response in ITP, two MAIPA (Monoclonal Antibody (MAb) Immobilization of Platelet Antigen) assays (MAIPA I and MAIPA II) were performed on sera from thrombocytopenic patients. In the classic MAIPA assay (MAIPA I), control platelets were incubated simultaneously with human serum and a mouse MAb to a platelet glycoprotein. In MAIPA II, the control platelets were incubated first with the human serum and then, after washing, with the selected mouse MAb. A positive MAIPA I test but a negative MAIPA II has been shown to result from the presence of serum antibodies recognizing mouse MAb to platelet glycoproteins used in the assay. We compared the frequency of such 'anti-mouse' antibodies in patients with thrombocytopenia associated or not with other autoimmune states and in healthy donors with a normal platelet count. Statistically significant differences were found in the incidence of anti-mouse antibodies between patients and healthy donors. Furthermore, the identity of the targeted mouse MAbs varied in sera from the patients. The detected anti-mouse antibodies may include anti-idiotypic antibodies produced against cross-reactive idiotypes shared by human and mouse anti-platelet antibodies.

Inhibition of primates performed xenoantibody binding to pig aortic endothelial cells and its potential application to xenotransplantation

IgM xenoantibodies are believed to play the most important role in the hyperacute rejection of distantly related species. The purpose of this study was to determine whether DL-Penicillamine could inactivate binding and cytotoxicity of adult baboon performed xenoantibodies to pig endothelial cells. Different concentrations of DL-Penicillamine were used to treat pooled baboon serum over various lengths of time. In order to determine the reactivity of baboon natural xenoantibodies to pig endothelial cells complement-mediated cytotoxicity assay was used. ELISA assay was used to assess IgM and IgG binding to pig endothelial cells. Subsequently DL-Penicillamine was dialyzed to determine its potential clinical application. Results indicate that baboon performed xenoantibodies class IgM and IgG bind to pig endothelial cells, but only IgM xenoantibody is cytotoxic DL-Penicillamine treatment can significantly reduce cytotoxicity and eliminate binding of IgM xenoantibodies to pig endothelial cells despite continued binding of IgG xenoantibodies to pig endothelial cells. In addition, DL-Penicillamine can be dialyzed, suggesting that it may be applicable in xenotransplantation and its toxicity can be significantly reduced by routine hemodialysis.

Human NK cell-mediated direct and IgG-dependent cytotoxicity against xenogeneic porcine endothelial cells

Once hyperacute rejection has been prevented, the pig-to-human xenograft might be exposed to vascular cell-mediated rejection directed against vascular structures. In order to evaluate the relative importance of direct and antibody-dependent anti-endothelial cell-mediated cytotoxicity in different individuals, freshly isolated human blood leukocytes were incubated with confluent porcine aortic endothelial cells (PAEC) in a 4 h Cr-release cytotoxicity assay. Peripheral blood mononuclear cells (PBMC) and lymphocytes (PBL) of all subjects tested (but not monocytes or neutrophils) directly killed PAEC, with wide interindividual variations (from 2.8% to 32%). The addition of heat-inactivated autologous serum to PBMC and PBL (but not to myeloid cells) always enhanced cytotoxicity. This antibody-dependent cell-mediated cytotoxicity (ADCC) was also observed in the presence of adult pooled serum and cord blood pooled serum and was eliminated after adsorption of adult pooled serum to insoluble protein A, demonstrating that IgG is the only class of immunoglobulin involved in this phenomenon. Moreover, blocking Fc gamma RIII with an anti-CD16 mAb eliminated ADCC without affecting direct cytotoxicity. When the ADCC exerted by the PBL of all subjects was assessed with the same preparation of purified IgG, wide interindividual variations were again observed. Surprisingly, there was no correlation between direct cytotoxicity and ADCC although, as depletion experiments demonstrated, both were due to CD16+ natural killer (NK) cells. These results argue that CD16+ NK cells could play an important role in early vascular rejection of porcine discordant xenografts, by both a direct and an IgG xenoreactive natural antibody-dependent cell-mediated cytotoxicity.

Preferential association of V lambda x light chains with gamma 2a heavy chains in naturally occurring human myelin basic protein reactive antibodies

Active immunization with myelin basic protein (MBP) induces experimental allergic encephalomyelitis (EAE) in a variety of animal species, including rats and mice. We have previously described the ability of the newly described mouse lambda (lambda) variable (V) region V lambda x, to confer MBP reactivity to an Ab. In this report, we have evaluated the heavy (H) chain isotype distribution of V lambda x-bearing Abs in normal mouse serum. We demonstrate a biased H chain isotype association with V lambda x light (L) chains with a skewing towards gamma 2a and 2b isotypes. The IgG2a restriction in normal mouse Igs is even more evident in V lambda x-containing Abs that bind MBP. This was confirmed by the ability of purified polyclonal IgG2a Abs to bind MBP and the finding that most or all of the IgG2a Abs that bind MBP seem to harbor a V lambda x L chain. The specificity of naturally-occurring V lambda x-bearing Abs with MBP can be localized to a particular epitope encompassing residues 25-34 of the MBP molecule. Furthermore, virtually all of the reactivity of V lambda x-containing Abs with MBP peptide 25-34 is associated with the gamma 2a isotype. Collectively, these results suggest that the interaction of V lambda x with MBP seems to be facilitated by an association with gamma 2a which may reflect preferred VH usage by this isotype. Such unique pairing of particular H chains with V lambda x L chains in Abs that bind MBP may be indicative of a new B-cell component involved in the pathogenesis of EAE.

Comparison between aortic and sinusoidal liver endothelial cells as targets of hyperacute xenogeneic rejection in the pig to human combination

Endothelial cells of aortic origin are usually used in vitro as targets of hyperacute xenogeneic rejection, although endothelial cells from organs may have different properties. The sensitivities of aortic and liver endothelial cells to hyperacute xenogeneic rejection were compared in the pig to human combination. Sinusoidal liver endothelial cells were isolated and purified by collagenase perfusion of pig livers, sedimentation on a percoll gradient and selective adherence. Purity and viability of isolated liver endothelial cells after adherence were 85+/-6% and >95%, respectively. Endothelial cells from pig aortae (purity and viability >95%) were isolated by scraping. Immunoblotting analysis of xenoantigens on liver and aortic endothelial cell membranes preparations showed identical patterns. The strongest bands revealed by human IgM were located between 110 and 135 kD, while human IgG detected two major bands at 115 and 75kD. The membrane expression of xenoantigens recognized by human sera, analyzed by flow cytometry, was significantly lower on liver than on aortic endothelial cells (IgM: P=0.0006; IgG: P=0.0009). However, the complement-dependent cytotoxic activity of human sera was the same whether liver (54.5+/-1.4%) or aortic endothelial cells (50.0+/-4.2%) were used as targets. Taken together, those results allow the use of aortic instead of sinusoidal liver endothelial cells in the characterization of pig antigens recognized by human natural antibodies.

Cell and extracellular matrix rejection in arterial concordant and discordant xenografts in the rat

Vascularized xenografts are rejected acutely and hyperacutely in concordant or discordant combinations, respectively. We investigated the impact of the donor-recipient combination on the rejection of arterial xenografts, analyzing the cellular and extracellular matricial compartments. Aortic xenografts were performed in a concordant (hamster) and a discordant (guinea pig) combination with Lewis rat. Graft cells and immune effectors were characterized by immunohistochemistry after 15 min and up to 30 days postimplantation. Macroscopic and microscopic structure of the grafts was studied at 60 days. IgC in the concordant combination and C3, C5b9, and IgM in the discordant combination deposited on endothelial cells, acutely and hyperacutely, respectively. The same immune effectors deposited on medial smooth muscle cells, but later than on endothelial cells. In both combinations the medial extracellular matrix was covered by IgM and IgC and infiltrated by monocytes (90%) and T lymphocytes (10%), with elastinolysis in the vicinity of monocytes. However, elastin resorption in the media at day 60 differed in concordant and discordant xenografts(75+/-10% and 99+/-1%, respectively). Intimal thickening and aneurysm developed in concordant and discordant combinations, respectively. Unlike arterial allografts, arterial xenografts are not a homogeneous group. The donor-recipient combination determines the mechanism and the timing of graft cell rejection, as well as the magnitude of medial elastin injury. As a consequence, chronic graft remodeling differs in the two combinations.

Monoclonal antiidiotypic antibodies neutralize cytotoxic effects of anti-alphaGal antibodies

The aims of this study were to produce and characterize mouse monoclonal antiidiotypic antibodies (AIAs) that specifically bind human antipig (anti-alphaGal) antibodies and to select those AIAs that neutralize the cytotoxicity of human or baboon serum to pig (PK15) cells. Mice were immunized with human anti-pig antibodies, and hybridomas were produced using conventional techniques. From a total of 480 clones, 11 produced AIAs that bound with high affinity to human anti-alpha Gal IgG and F(ab')2 fragments, and individually reduced serum cytotoxicity to pig cells by 40 - 90%. Seven of the AIAs also bound to human peripheral B lymphocytes (that express the same idiotypes as the antibodies produce). Several combinations of two or three AIAs provided 100% protection of PK15 cells. Selected AIAs injected intravenously into baboons reduced the cytotoxicity of subsequently drawn sera by 50--80% for >48 hr. The cytotoxicity studies also indicated that there are at least two dominant idiotypes expressed in the human anti-alphaGal population. We conclude that AIAs against anti-alphaGal antibodies could be successfully used in 1) preoperative characterization of a recipient's anti-alphaGal profile, (2) prevention of hyperacute rejection of a pig organ, and (3) specific immunosuppression through elimination of anti-alphaGal-producing B lymphocytes.

[A patient showing increased T3 and T4 levels due to ALP-interfering substances and heterophilic antibody]

A 73-year-old male, who underwent resection of soft palate cancer and was under treatment for esophageal ulcer at our medical department, complained of palpitation. On the suspicion of hyperthyroidism, enzyme immunoassay (EIA) was performed. T3 and T4 were increased, and FT4 and TSH were normal. However, T3 and T4 measured again by radioimmunoassay (RIA) were normal. Therefore, the patient serum was examined for interfering substances such as antibody against bovine intestinal alkaline phosphatase (ALP) and heterophilic antibody. Substances interfering with ALP and anti-rabbit IgG human antibody were detected. It is necessary to consider the possible presence of these substances when results of EIA are evaluated.

Tumor necrosis factor-induced expression of porcine glycoproteins gp65 and gp100 recognized by human xenoreactive natural antibodies

In the pig-to-primate model of xenotransplantation, graft rejection is initiated by binding of the recipient's xenoreactive natural antibodies (XNA), mainly of the IgM type, to antigens constitutively expressed on donor endothelial cells (EC). As a consequence of XNA binding and complement fixation, the EC become activated, which is considered to be a major mechanism promoting hyperacute as well as later phases of graft rejection. It is not clear whether binding of XNA to activated EC also contributes to delayed rejection. We asked whether EC activation by cytokines results in the expression of other novel surface antigens recognized by XNA which might become relevant in progressive stages of graft rejection. We activated porcine aortic EC and smooth muscle cells with tumor necrosis factor (TNF), interleukin 1, or lipopolysaccharide and studied expression of new XNA-binding antigens. Expression of two glycoproteins, gp65 and gp100, was strongly induced by recombinant human TNF in EC but not in smooth muscle cells. Notably, gp100 expression was specific to TNF activation, whereas gp65 could also be induced by interleukin 1 or lipopolysaccharide. Cell surface labeling indicated that gp65 is expressed on the plasma membrane. Recognition of XNA-binding antigens on resting EC occurs via alpha-galactosyl epitopes. In contrast, gp65 and gp100 were recognized independently of this epitope. Our data show that gp65 and gp100 represent selective cytokine-induced markers on EC that may have importance in a porcine-to-primate model of xenotransplantation. Conceivable functions of gp65 and gp100 are discussed.

Pig alpha1, 3galactosyltransferase: a major target for genetic manipulation in xenotransplantation

Terminal carbohydrate residues of glycolipids and glycoproteins display polymorphism among as well as within various species. With the exception of Old World monkeys, great apes and man, the Gala1,3Gal structure is widely expressed in all mammals examined so far. The lack of expression of the glycosyltransferase responsible for the synthesis of Gala1,3Gal leads to the production of high titers of natural antibodies (NAb) against the Gala1,3Gal of other species. The inactivation of this gene occurred during early evolution of primates. Neutralization of viruses (e.g. retroviruses) carrying the epitope, by the pre-formed human NAb, indicates one possible evolutionary reason for the polymorphism of terminal carbohydrates among as well as within species. It has been shown that this epitope constitutes the major target, on pig endothelial cells (EC), for the pre-formed human NAb resulting in a hyperacute rejection (HAR) response. This currently makes transplantation of e.g. pig organs to humans impossible. Efforts are currently underway to prevent or to eradicate the expression of this epitope in transgenic pigs. Such pigs are likely to display a greatly increased resistance to the HAR.

Specificity of xenoreactive anti-Gal alpha 1-3Gal IgM for alpha-galactosyl ligands

The transplantation of organs from lower animals such as pigs into humans is prevented by a severe rejection reaction initiated by complement fixing xenoreactive natural antibodies. Most anti-pig xenoreactive natural antibodies in humans are thought to recognize Gal alpha 1-3Gal beta 1-4GlcNAc and are also thought to recognize, albeit less avidly, Gal alpha 1-6Glc. Gal alpha 1-6Glc has been used as a ligand for purification of 'anti-Gal alpha 1-3Gal antibodies' and as a therapeutic or reagent to prevent the binding of these antibodies to porcine organs or cells. We tested the specificity of anti-Gal alpha 1-3Gal IgM for Gal alpha 1-6Glc and related saccharides. Based on inhibition of binding of xenoreactive anti-Gal alpha 1-3Gal IgM to porcine cells by soluble saccharides, anti-Gal alpha 1-3Gal IgM in a human serum was found to consist of a mixture of antibodies which have a similar affinity for Gal alpha 1-3Gal but varying affinities for Gal alpha 1-6Glc and other structures. Twenty to 40% of the anti-Gal alpha 1-3Gal IgM from the population tested did not recognize Gal alpha 1-6Glc. The binding of anti-Gal alpha 1-3Gal IgM to Gal alpha 1-6Glc varied widely from individual to individual, some samples lacking almost entirely anti-Gal alpha 1-3Gal IgM which bound to Gal alpha 1-6Glc.

Characterization of porcine platelet glycoproteins recognized by human natural "anti-gal" antibodies

Human natural "anti-Gal" antibodies are specifically directed to Gal alpha 1-3Gal beta 1-4GlcNAc residues expressed on non-primate mammal and new world monkey cells. We investigated the relative involvement of purified IgG and IgM anti-Gal as xenoreactive natural antibodies (XNA). IgG and IgM were isolated from human plasma, and anti-Gal antibodies were purified by affinity chromatography on a Synsorb-14 column (Chembiomed, Edmonton, Alberta, Canada). Anti-Gal of both IgM and IgG classes represent the bulk of human XNA that bind to porcine platelets in enzyme-linked immunosorbent assay (ELISA). On immunoblots, normal human sera, as well as purified IgM and IgG fractions, reacted with 115-, 125-, 135-, 150-, 180-, 210-, and 240-kd) pig platelet proteins, whereas purified anti-Gal antibodies of both IgM and IgG classes mainly bound to 135-, 150-, 180-, and 210-kD glycoproteins. A low reactivity was observed in ELISA with anti-Gal free IgM and IgG, indicating that xenoantibodies are not solely directed to galactosyl epitopes. These antibodies revealed bands of 115, 125, and 240 kD, alpha-Galactosidase treatment of porcine platelet glycoproteins (gps) enriched by affinity chromatography abrogated the reactivity of 135- and 210-kD proteins. N- and O-glycosidase treatments demonstrated that alpha-galactosyl residues are located on the O-glycans of the 135-kD component. Finally, glycoproteins of 90 and 135 kD were identified by amino acid sequencing as the pig analogs of the human glycoproteins IIIa and IIb, respectively, whereas the 240-kD) component was identified as the porcine fibrinogen, using a new murine monoclonal antibody (naM147-7B6; IgG1) specific for its beta-chain.

Neutralization of myonecrosis, hemorrhage, and edema induced by Bothrops asper snake venom by homologous and heterologous pre-existing antibodies in mice

The ability of pre-existing antibodies to neutralize locally-acting toxins of Bothrops asper snake venom was investigated. Hemorrhage, myonecrosis, and edema were markedly reduced in actively immunized mice, although none of these effects was completely abolished. In mice passively immunized with equine antivenom, hemorrhage was prevented completely, while myonecrosis and edema were partially reduced. Pre-existing antibodies did not modify the early stage (< 3 hr) of venom-induced edema, but significantly accelerated the normalization of this effect within 24 hr. Passive administration of antivenom either 5 or 120 min before venom injection gave similar results, suggesting that the presence of antibodies in the intravascular compartment may fully neutralize locally acting toxins, in this experimental animal model. Overall, the homologous or heterologous origin of antibodies was not a significant factor influencing their in vivo neutralizing efficiency against local venom effects. Antibody titrations by enzyme-immunoassay using purified toxins and whole venom indicated that serum from actively-immunized mice had a higher proportion of anti-myotoxin antibodies than equine antivenom.

Different action of xenoreactive natural and immune antibodies on functioning cardiomyocytes

PNAB and IAB have totally different action on BCM. PNAB inhibit the contractile function of BCM by producing a reversible standstill and by disturbing the synchronization of the BCM-monolayer. IAB are cytotoxic and depend on the presence of complement.

The alpha-1,3-galactosyltransferase knockout mouse. Implications for xenotransplantation

Organ xenografts in discordant combinations such as pig-to-man undergo hyperacute rejection due to the presence of naturally occurring human anti-pig xenoantibodies. The galactose alpha(1,3)-galactose epitope on glycolipids and glycoproteins is the major porcine xenoantigen recognized by these xenoantibodies. This epitope is formed by alpha(1,3)-galactosyltransferase, which is present in all mammals except man, apes, and Old World monkeys. We have generated mice lacking this major xenoantigen by inactivating the alpha(1,3)-galactosyltransferase gene. These mice are viable and have normal organs but develop cataracts. Substantially less xenoantibody from human serum binds to cells and tissues of these mice compared with normal mice. Similarly, there is less activation of human complement on cells from mice lacking the galactose alpha(1,3)-galactose epitope. These mice confirm the importance of the galactose alpha(1,3)-galactose epitope in human xenoreactivity and the logic of continuing efforts to generate pigs that lack this epitope as a source of donor organs.

Lysis of human tumor cell lines by canine complement plus monoclonal antiganglioside antibodies or natural canine xenoantibodies

Because certain antiganglioside monoclonal antibodies can facilitate antibody-dependent cellular cytotoxicity against GD2+ ganglioside-bearing human and canine tumor cells, we wished to determine if clinically relevant antiganglioside monoclonal antibodies (Mabs) could also fix canine complement to lyse tumor cells in vitro. Using flow cytometry, human tumor cell lines (M21 melanoma and OHS osteosarcoma) were shown to highly express ganglioside GD2 and, to a lesser degree, GD3. In 51Cr release assays, M21 cells were lysed with canine serum, as a source of complement, plus either Mab 14.G2a or its mouse-human chimera, ch 14.18, specific for GD2. Heating canine serum abrogated its lytic activity and addition of rabbit complement reconstituted M21 lysis. Similar results were obtained with M21 cells when Mab R24 (against GD3) and canine serum were used. OHS cells were also lysed with canine serum plus Mab 14.G2a and lytic activity was abolished by heating canine serum but reconstituted with rabbit complement. Alone, canine serum or Mabs were not lytic to M21 or OHS cells. Conversely, human neuroblastoma (LAN-5) and K562 erythroleukemia cells were lysed by canine serum alone which was shown by flow cytometry to contain naturally occurring canine IgM antibodies that bound LAN-5 and K562 cells. The lytic activity of canine serum for LAN-5 or K562 cells was abolished by heating and restored by addition of either human or rabbit complement. Thus, human tumor cell lines can be lysed with antiganglioside Mabs through fixation and activation of canine complement-dependent lytic pathways. Canine xenoantibodies also mediate complement-dependent cytotoxicity of some human tumor cell lines. Together, these results are significant because they demonstrate an antitumor effect of the canine immune system which is of potential importance for cancer immunotherapy in a promising animal model.

The humoral immune response in humans following cross-perfusion of porcine organs

A major question in xenotransplantation is the nature of the humoral response that would occur following the transplantation of a xenogeneic organ into an immunosuppressed recipient as such a response could mediate delayed types of injury to the graft. To begin to address this issue we characterized the changes in the properties of xenoreactive antibodies occurring in patients exposed to porcine organs under conditions simulating transplantation. In two patients whose blood had been cross-perfused through porcine livers as a treatment for hepatic failure, the titer of xenoreactive IgM increased by four-fold and the titer of xenoreactive IgG increased by sixty-fold within ten days after perfusion procedures. The xenoreactive IgM and IgG antibodies were specific for Gal alpha 1-3Gal based on binding to porcine endothelial cells and bovine thyroglobulin, which express this determinant, and on the decrease in binding following treatment of porcine endothelial cells or bovine thyroglobulin with alpha-galactosidase. The sequential addition to endothelial cells of amounts of serum known to saturate antibody-binding sites obtained before and ten days after perfusion of porcine organs revealed no increase in binding of IgM above the level observed with serum obtained before perfusion, suggesting that new determinants were not identified. Moreover, the functional avidity of binding to porcine endothelial cells of IgM in serum obtained before and ten days after perfusion of porcine organs was unchanged. Even at later times, the presence of newly elicited antibodies against porcine aortic endothelial cell targets was not detected. Thus, exposure to porcine antigens in a vascularized organ results in increases in the levels of xenoreactive IgM and IgG antibodies--however, these antibodies exhibit properties similar to natural antibodies.

Age-related development of human anti-pig xenoantibody

Human cytotoxic natural xenoantibodies are believed to be of the immunoglobulin M class in nature. However, a thorough understanding of the development of these natural antixenodonor xenoantibodies remains incomplete. In this study, serum samples were obtained from newborn, infant, and adult human beings. An enzyme-linked immunosorbent assay was used to determine the binding of human natural immunoglobulin M xenoantibodies to pig aortic endothelial cells and pig lymphocytes. A complement-mediated cytotoxicity assay was used to measure the cytotoxicity of newborn, infant, and adult serum to cultured pig aortic endothelial cells and pig lymphocytes. Adult human serum contained both natural immunoglobulin M and immunoglobulin G xenoantibodies to pig endothelial cells and lymphocytes, whereas newborn infant serum contained only immunoglobulin G xenoantibodies. Only adult human serum was cytotoxic to pig endothelial cells and lymphocytes. Human immunoglobulin M xenoantibodies became detectable by age 1 month. By age 2 months these natural anti-pig xenoantibodies reached serum levels equivalent to those in the human adult and resulted in similar cytotoxicity to that of adult human serum. These findings indicate that (1) natural anti-pig immunoglobulin M xenoantibodies are absent from newborn infant human serum, (2) newborn human serum is not cytotoxic to pig endothelial cells and lymphocytes despite the presence of immunoglobulin G xenoantibodies that bind to pig endothelial cells and lymphocytes, and (3) natural anti-pig immunoglobulin M xenoantibodies begin to develop as early as age 1 month and by age 2 months attain a circulating level comparable to that found in the adult.

Natural antipig xenoantibody is absent in neonatal human serum

BACKGROUND

Discordant xenotransplantation represents an attractive alternative to allotransplantation in light of the current shortage of donor organs suitable for heart allotransplantation. Unfortunately, discordant xenotransplantation is still limited by hyperacute rejection, a process thought to be mediated by natural antixenodonor antibodies. On the basis of our previous findings that cytotoxic natural xenoantibodies are immunoglobulin M in nature and that natural immunoglobulin M xenoantibodies are barely detectable in neonatal baboon serum, we postulated that immunoglobulin M xenoantibodies may be absent from newborn human serum.

METHODS

Neonatal human sera were obtained from the cord blood of normal term infants and pooled. Pooled adult human sera were used as a control. A whole cell enzyme-linked immunosorbent assay and a complement-mediated cytotoxicity assay were performed to determine the binding and cytotoxicity of these xenoantibodies to pig aortic endothelial cells and pig lymphocytes.

RESULTS

Neonatal human sera did not show binding of immunoglobulin M xenoantibodies to pig aortic endothelial cells or lymphocytes. However, low level binding of immunoglobulin G xenoantibodies was detected to pig endothelial cells and lymphocytes. In contrast, adult human sera showed significant binding of both natural immunoglobulin M and G xenoantibodies to pig aortic endothelial cells and lymphocytes. In addition, adult human immunoglobulin M xenoantibodies bound with similar avidity to both cultured adult and neonatal pig aortic endothelial cells. Although neonatal human sera were not cytotoxic to target cells, adult sera were cytotoxic to both pig aortic endothelial cells and pig lymphocytes. Our findings indicate that neonatal human sera lack natural antipig immunoglobulin M xenoantibodies, and therefore, neonatal human serum is not cytotoxic to pig endothelial cells or lymphocytes. Like adult pig endothelial cells, neonatal pig endothelial cells may also express similar membrane xenoantigens recognized by natural immunoglobulin M xenoantibodies.

CONCLUSIONS

The absence of cytotoxic natural immunoglobulin M xenoantibodies in the neonate suggests that discordant xenotransplantation may be feasible in the neonate.

Toxicological consequences of aroclor 1254 ingestion by female rhesus (Macaca mulatta) monkeys. Part 2. Reproduction and infant findings

A group of 80 menstruating rhesus (Macaca mulatta) monkeys were randomly allocated to four similar test rooms (20 monkeys/room) and then randomly allocated within each room to one of five dose groups (four females/dose group/room). Each day, the monkeys self-ingested capsules containing doses of 0, 5, 20, 40 or 80 micrograms Aroclor 1254/kg body weight. After 25 months of continuous dosing, approximately 90% of the treated females had attained a qualitative pharmacokinetic steady state with respect to the concentration of polychlorinated biphenyl (PCB) in their adipose tissue. Commencing on test month 37, each female was paired with an untreated male until either an impregnation occurred or the 29-month breeding phase of the study was completed. The females continued to receive their daily test dose during mating and gestation. To preclude an infant ingesting the mother's dosing capsule, dosing of the dam was discontinued when a nursing infant was approximately 7 wk old. Treatment was restarted when the infant was weaned at 22 wk of age. At parturition, and every 4 wk until weaning, milk and blood samples were obtained from the dam and a blood sample was obtained from the infant for PCB analysis. When the infant was 20 wk old, immunological testing was initiated and an adipose sample was obtained from the infant and dam for PCB analysis. Subsequently, further adipose and blood samples were obtained from the infant and blood specimens were obtained from the dam for PCB analysis. Concurrently, each infant was subjected to anthropometric measurements and detailed clinical examinations until it was approximately 122 wk old. At 122 wk some of the control and all of the treated infants were killed humanely and autopsied. A statistical analysis of the reproduction data provided evidence for a significant decreasing dose-related trend in conception rates and a significant increasing dose-related trend in foetal mortality. Several comparisons between impregnated and non-impregnated females did not implicate 'age' as a confounding factor regarding these results. The major findings with the infants involved some immunological test differences and mild clinical manifestations of PCB ingestion.

Identification of porcine endothelial cell membrane antigens recognized by human xenoreactive natural antibodies

Rejection of an organ transplanted into a phylogenetically disparate recipient may be initiated by the binding of xenoreactive natural Abs of the recipient to Ags expressed on donor endothelium leading to the activation of the C system. Having previously shown that human xenoreactive Abs bind predominantly to N-linked oligosaccharides on porcine endothelial cell glycoproteins, we sought to identify those glycoproteins to gain insight into the pathogenesis of the rejection reaction and to develop improved methods for depleting those Abs. Based on amino-terminal and internal sequencing of the glycoproteins, reactivity with monospecific rabbit Abs, and functional properties, the porcine endothelial cell targets of human natural Abs were shown to be the von Willebrand factor, integrin alpha 1, alpha v, alpha 3/alpha 5, beta 1, and beta 3 chains and a 95-kDa glycoprotein homologous with chick DM-GRASP. Human and baboon Abs directed against those glycoproteins were shown to be absorbed during perfusion of porcine organs and the binding of human IgM to the isolated glycoproteins to initiate the activation of C leading to formation of iC3b neoantigen. The determinants recognized by human xenoreactive Abs had immunodominant alpha-galactosyl residues based on affinity chromatography, reactivity with anti-Gal alpha(1-3)Gal Abs and sensitivity to alpha-galactosidase. The findings show that members of the integrin family and the von Willebrand factor are major targets of xenoreactive Abs and suggest potential mechanisms by which the binding of Abs to endothelial cells might perturb the physiology of those cells and thus cause aberrant functioning of a tissue or organ.

Production of monoclonal antibodies directed to Hanganutziu-Deicher active gangliosides, N-glycolylneuraminic acid-containing gangliosides

We have established three kinds of monoclonal antibodies against gangliosides containing N-glycolylneuraminic acid (NeuGc) by immunization of BALB/c mice with the purified gangliosides inserted into liposomes comprising Salmonella minnesota R595 lipopolysaccharides, and fusion of spleen cells with a mouse myeloma cell line. One monoclonal antibody, SHS-1, which was generated by immunizing mice with purified i-active ganglioside(NeuGc), reacted specifically with the i-active ganglioside(NeuGc) used as an immunogen. Structurally related gangliosides, such as GM3(NeuGc), sialosylparagloboside (SPG) (NeuGc), or I-active ganglioside(NeuGc), corresponding gangliosides [GM3 containing N-acetylneuraminic acid (NeuAc), SPG(NeuAc), i-active ganglioside(NeuAc), and I-active ganglioside(NeuAc)], other gangliosides, or neutral glycosphingolipid (GSL) were not recognized by the monoclonal antibody. These findings indicate that the SHS-1 monoclonal antibody may be specific for NeuGc-containing i-active ganglioside. On the other hand, the other two monoclonal antibodies, MSG-1 and SPS-20, which were generated by immunizing mice with purified ganglioside GM3(NeuGc) and SPG(NeuGc), respectively, showed cross-reactivity to structurally related gangliosides. The MSG-1 monoclonal antibody exhibited reactivity to ganglioside GM3(NeuAc). The SPS-20 monoclonal antibody also cross-reacted with SPG(NeuAc), i-active ganglioside(NeuGc), and i-active ganglioside(NeuAc). Neither MSG-1 nor SPS-20 reacted with corresponding gangliosides, other gangliosides, or neutral GSLs tested. Using the SHS-1 antibody specific for i-active ganglioside(NeuGc), we studied the expression of NeuGc-containing antigen in human colon cancer tissue. An NeuGc-containing glycoconjugate was detected in the colon cancer tissue.

Reducing interference from heterophilic antibodies in a two-site immunoassay for carcinoembryonic antigen (CEA) by using a human/mouse chimeric antibody to CEA as the tracer

To reduce heterophilic antibody interference in a two-site immunoassay for carcinoembryonic antigen (CEA), we utilized a human/mouse chimeric antibody to CEA as the tracer. One mouse monoclonal antibody (MAb), F82-61, which reacts with an epitope present on the domain N of CEA, was immobilized on 96-well polystyrene microtiter plates. A human/mouse chimeric antibody (Ch F11-39), which recognizes an epitope present on the domain B3 of CEA, was biotinylated for the tracer (Ch F11-39 system). Another MAb F11-39, the parental MAb of Ch F11-39, was also biotinylated and used as the control tracer (F11-39 system). For a fair comparison, the same 503 serum samples from healthy individuals were simultaneously assayed in the present study. When a tentative common reference limit of 5 ng/ml was used, the false positive rate with the Ch F11-39 system was only 2.8% (14/503) and that with the F11-39 system was 29.0% (146/503). Adding normal mouse serum (NMS; 1%) or a mixture of purified mouse IgG subclasses (heterophilic blocking reagent (HBR, 15 micrograms/test)) to the F11-39 system reduced the false positive rate from 29.0% to 6.2% (31/503) or 4.8% (24/503), respectively, suggesting that heterophilic antibodies reactive with mouse IgG gave rise to the high positive rate in normal populations with the F11-39 system. On the other hand, the false positive rate with the Ch F11-39 system was only slightly reduced from 2.8% to 2.6% (13/503) or to 2.0% (10/503) by adding NMS or HBR to the Ch F11-39 system. The false positive rates with two commercially available assay systems, CEA Roche EIA.DM or Abbott IMx CEA, were 5.4% (27/503) and 5.8% (29/503), respectively, which both corresponded roughly to that with the F11-39 system including NMS or HBR. These results indicate that the application of human/mouse chimeric antibodies in two-site immunoassays is more effective for reducing interference from heterophilic antibodies than the adding of NMS or purified mouse IgG in the assay using conventional MAbs.

Differential patterns of reaction of human natural antibodies to pig hepatocytes and vascular endothelium

We have recently conducted a series of experiments to characterize the pattern of reaction of human natural antibodies (NA) with individual pig liver cells. Pooled normal human serum (PHS) was incubated with cultured pig hepatocytes (HEP), aortic endothelial cells (AEC), and portal endothelial cells (PEC), and the reaction of NA to different cell types was measured by antibody-mediated cytotoxic (MTT assay), antibody binding (ELISA), and flow cytometric analysis. The human NA displayed a differential pattern of binding with hepatocytes exhibiting a more limited expression of xenoantigen expression than either aortic or portal endothelial cells. These differences in reaction patterns were also noted for Western blot analysis of individual cell membrane extracts. Preincubation of the pig cells with anti-pig MHC antibodies did not inhibit the binding of human IgM natural antibodies to the pig cells. Comparison of the pattern of NA absorption following the use of bioartificial liver support in patients with acute hepatic failure demonstrated limited ability of pig hepatocytes to absorb substantial amounts of NA. These studies indicate that pig hepatocytes are less vulnerable to NA cytotoxicity than pig vascular endothelial cells and that pig vascular endothelial cells express xenoantigens that are unique and not found on hepatocytes.

Inhibition of bispecific monoclonal antibody (bsAb)-targeted cytolysis by human anti-mouse antibodies in ovarian carcinoma patients treated with bsAb-targeted activated T-lymphocytes

T lymphocytes of 8 patients with ovarian cancer were targeted to the tumor cells using F(ab')2 fragments of a bispecific monoclonal antibody (bsAb), specific for CD3 (a component of the T lymphocyte receptor for antigen) and for the folate receptor MOv18 (overexpressed by ovarian carcinoma cells) as part of a phase I/II study. Phase I (days 0 to 3) consisted of increasing intraperitoneal (i.p.) numbers (10(6)-10(9)) of bsAb-targeted T lymphocytes plus low-dose interleukin-2 (IL-2). Phase II (days 6 to 13, and 27 to 33) consisted of daily i.p. infusions of 10(9) targeted T lymphocytes, 2 mg soluble bsAb, and low-dose IL-2. Using enzyme-linked immunosorbent assays (ELISA), human anti-mouse antibodies (HAMA) were detected in all patients: in the serum from day 13 onwards and in the peritoneal fluid from day 20 onwards. A significant proportion of the HAMA appeared to be directed against the idiotypes of the bsAb specific for CD3 and MOv18, as suggested by (1) the clearly higher ELISA titers against OC/TR bsAb as compared to those against a monoclonal antibody (MAb) with unrelated specificity, and (2) failure to abrogate the capacity of peritoneal fluid containing HAMA to block the binding of OC/TR bsAb to MOv18+ or CD3+ cells by absorption of human anti-mouse IgG-framework antibodies in peritoneal fluid to immobilized mouse IgG. The OC/TR-targeted cytolysis of the MOv18+ ovarian carcinoma cell line Igrov-I by autologous T lymphocytes was inhibited by peritoneal fluid samples containing relatively high HAMA titers. Such inhibitory activity was never detected at the start of phase II, but coincided with the last series of i.p. infusions of targeted T lymphocytes in 2 patients.

Structure and pathophysiology of the erythrocyte membrane-associated Paul-Bunnell heterophile antibody determinant in Epstein-Barr virus-associated disease

Epstein-Barr virus (EBV), which was first isolated by Epstein, Barr, and Achong (1964) from a cultured Burkitt's lymphoma lymphoblast cell line, is the etiological agent for infections mononucleosis (IM), polyclonal oligoclonal lymphomas associated with primary and acquired immunodeficiencies, and the complications of X-linked lymphoproliferative syndrome (XLP) (Cantani and Mastrantoni, 1989; Englund, 1988; Ernberg et al., 1990; Jones and Straus, 1987; Okano et al., 1988; Purtilo et al., 1981; Shearer et al., 1985; Wilmes and Wolf, 1989). EBV also contributes to the pathogenesis of Burkitt's lymphoma (Frizzera, 1987; Harrington et al., 1988; Henle et al., 1968; Purtilo et al., 1981; Rowe et al., 1986; Saemundsen et al., 1981) and nasopharyngeal cancer (Pearson et al., 1984). Furthermore, people who have had IM have higher rates of subsequent development of malignant lymphoproliferative disorders (Abo et at., 1982; Snydman et al., 1982) and Hodgkin's disease (Green et al., 1979; Mueller, 1987; Poppema et al., 1985; Weiss et al., 1989), while patents with XLP have a higher incidence of non-Hodgkin's malignant lymphoma (Harrington et at., 1987). The precise role of EBV in these diseases is not well understood. Nonetheless, it is known that EBV infection triggers the formation of heterophile antibodies that, for many decades, have formed the basis for serologic diagnosis of IM. In this review, we discuss the discovery, species variation, and structure of the erythrocyte membrane-associated Paul-Bunnell (PB) heterophile antibody determinant, its implications to IM diagnosis, and its potential contribution to defective immune surveillance and associated uncontrolled proliferation of EBV-infected cells.

Abrogation of baboon natural xenoantibody to pig splenocytes by DL-penicillamine

Natural xenoantibodies are believed to be IgM in nature and are known to play a critical role in the hyperacute rejection of distantly related xenografts. The purpose of this study was to determine whether the reducing agent DL-penicillamine could inactivate baboon natural xenoantibodies to pig splenocytes. Pooled baboon serum was treated with varying concentrations of DL-penicillamine over different lengths of time and a complement-mediated cytotoxicity assay was used to determine the reactivity of baboon natural xenoantibodies to pig splenocytes. A whole-cell ELISA assay was used to assess the binding of both IgG and IgM xenoantibodies to pig splenocytes. In addition, DL-penicillamine-treated serum was dialyzed to assess its potential clinical application. These in vitro experiments indicate that both IgM and IgG baboon natural xenoantibodies bind to pig splenocytes, but only IgM xenoantibody is cytotoxic. The binding of baboon natural IgM xenoantibody can be eliminated, and the cytotoxicity of IgM xenoantibody markedly reduced by DL-penicillamine treatment despite continued binding of IgG xenoantibody to pig splenocytes. In addition, DL-penicillamine can be dialyzed, suggesting that it may be an efficacious clinical treatment, the toxicity of which can be regulated with hemodialysis.

Beating neonatal rat cardiomyocytes as a model to study the role of xenoreactive natural antibodies in xenotransplantation

The hyperacute rejection reaction of xenogeneic organs is supposed to be triggered by xenoreactive natural antibodies of the recipient organism. In an experimental set-up allowing for rapid medium exchange, primary cultures of spontaneously beating neonatal rat cardiomyocytes were challenged with dialyzed human serum containing xenoreactive natural antibodies. After adding the serum specimens, a reproducible pattern of disturbed contractility was observed: following an initial increase in beating frequency, spontaneous contractions stopped completely. This standstill was reversible in all experiments. No signs of permanent cytotoxicity were observed. The temporary cessation of contractions was prevented by raising extracellular calcium concentration, but not by extracellular electrical stimulation. After absorption of xenoreactive natural antibodies, cellular contractions ensued without interruption. Inactivated serum specimens produced similar effects on contractility, although the duration of the standstill period was significantly shorter. The same qualitative phenomenon occurred when sera of other xenogeneic species were used. These results point to a temporary functional disturbance of parenchymal cells by xenoreactive natural antibodies, whereas no chronic cytotoxicity was conspicuous in these experiments.

Monomorphic and polymorphic carbohydrate antigens on pig tissues: implications for organ xenotransplantation in the pig-to-human model

The existence of the alpha Gal epitope in 137 pigs belonging to 23 different breeds suggests that this antigen is either monomorphic or occurs at a high incidence in the porcine species. Its histological location at the surface of pig vascular endothelial cells makes it a target for human natural anti-alpha Gal antibodies and complement, which may be responsible for the hyperacute vascular rejection of transplanted pig organs. The precursor carbohydrate chain (N-acetyllactosamine) and NeuAc-substituted epitopes are also exposed at the surface of pig vascular endothelium and were found in all pigs in this study. However, humans also have these two epitopes on vascular endothelium and, consequently, have not made natural antibodies against these carbohydrate antigens. Therefore, these two pig epitopes cannot be the main target of the hyperacute vascular rejection process. Three pig phenotypes-A+ (51%), A:H+ (38%), and A-H- I+ (11%) were identified among 37 Large-white pigs by the presence of polymorphic A, H, and I carbohydrate antigens on the brush border of the surface epithelium of small intestine. These antigens were also present in other exocrine secretions but were not detected on vascular endothelium of the same pigs, suggesting that they are not involved in the hyperacute vascular rejection, although the pig A tissue antigen can induce an immune response in 0 or B blood group recipients. Once the problem of the initial hyperacute vascular rejection directed against the alpha Gal epitope is overcome, typing donor pigs for A, H, and I, as well as for the protein swine leukocyte antigens (SLA) and other pig antigens, may help in elucidating antigens involved in acute or chronic xenograft rejection.