Disparate Species Research Articles

Taphonomic and Paleoenvironmental Evidence of Holocene Shell-Bed Genesis and History on the Northeastern Gulf of Mexico Shelf

Subsurface shell beds that are common on the eastern Alabama/western Florida Panhandle shelf provide paleoenvironmental and taphonomic data that demonstrate a dynamic depositional history with reactivation and amalgamation to the base of the Holocene marine transgressive package. In most of the ten shell beds we examined, shallow-marine mollusks, large soritid foraminifera, and cupularid bryozoans are common. Bioclasts occur in all preservation states, but a majority are pristine or only slightly altered. Normal grading, and concave-up, stacked, and random fabrics are common. In three of these shell beds, a relict estuarine component characterized by poorly-preserved Chione cancellata can be detected. Three other shell beds contain 1 of 2 estuarine molluscan assemblages. One assemblage is characteristic of fine-grained and the other of coarser-grained substrates. In all estuarine shell beds, bioclast preservation ranges from excellent to mixed, and bioclasts have random fabrics and locally are normally graded. Most molluscan remains are indigenous and assemblages range from within-habitat time-averaged to environmentally condensed. Shell beds are thick (up to about 75 cm) and overlie bay or shoreface ravinement surfaces, indicating that shell beds first accumulated as coarse transgressive deposits, and are composite concentrations modified by multiple events. Shell beds, however, are amalgamated. Only fabrics reflecting the final modifying events are preserved, and evidence of previous accumulation processes are obliterated. For marine shell beds especially, these final agents were, and possibly continue to be, highenergy events such as storms (winter cold fronts, hurricanes) or currents associated with Loop Current eddies. Episodically high sedimentation rates associated with these events may have acted as a buffer, preventing a long history of reworking and exposure (thus reducing shell alteration) typical of transgressive lags. Our results indicate that: 1) within-habitat time-averaged and environmentally condensed assemblages can be distinguished by combining taphonomic and environmental data, even when the ranges of environmentally disparate species overlap, 2) transgressive-lag deposits can be composed of well-preserved bioclasts, and 3) transgressive lags can be reworked and amalgamated but still be recognizable on the basis of their stratigraphic context.

Direct simulation of concentration creep in a binary gas-filled enclosure

A Cartesian, two-dimensional enclosure containing an isothermal rarefied binary gas mixture is studied as a limiting-case model for actual crystal growth experiments conducted in reduced gravity environments. By employing a microscopic approach related to the Boltzmann equation, it is demonstrated that in the presence of appreciable partial concentration gradients a steady-state flow pattern develops, driven by kinetic boundary layers adjacent to solid boundaries. In contrast, a macroscopic analysis based on the continuum transport equations and the classical no-slip boundary condition would predict no flow whatsoever. For the case of equal mass species, the velocity scales involved are shown to increase with the disparity in accommodation coefficients, in agreement with expectations based on one-dimensional, linearized Knudsen sublayer theory, while quantitative comparison between simulations and the latter theory reveals significant confinement effects. Simulation of concentration creep in binary mixtures composed of disparate mass species requires an alternative computational procedure, motivated by surface recombination/dissociation reactions. For this case, flow fields and creep coefficient values for a range of mass ratios are also reported. It is concluded that future continuum-level modelling efforts should more fully exploit the detailed information now available from relevant microscopic simulations.

Skin graft tolerance across a discordant xenogeneic barrier.

Specific T-cell tolerance may be essential for successful xenotransplantation in humans. Grafting of thymectomized, T cell-depleted normal mice with xenogeneic fetal pig thymus and liver (FP THY/LIV) tissue results in the recovery of functional CD4 antigen-positive cells. We have tested T-cell tolerance by skin grafting. Donor-matched pig skin survived permanently (> 200 days), whereas allogeneic mouse skin was rapidly rejected. Nontolerant control mice rejected pig skin within 26 days. Both porcine and murine histocompatibility class IIhigh cells were detected in long-term thymus grafts, and T-cell repertoire analyses suggested that tolerance to both donors and recipients developed, at least in part, by intragraft clonal deletion. This study demonstrates the principle that tolerance, measured by the stringent criterion of skin grafting, can be induced across a widely disparate species barrier.

Key role of the alternate complement pathway in hyperacute rejection of rat hearts transplanted into fetal sheep.

Hyperacute rejection (HAR) mediated by xenoreactive natural antibodies (XNA), which are thought to develop in early infancy, is a major impediment to transplantation between widely disparate species. The ability to diagnose certain forms of congenital heart defects early in prenatal life suggests the potential for these defects to be corrected by cardiac transplantation, prior to the development of XNA and host immunocompetence. This study investigated whether discordant cardiac xenotransplantation into fetal and neonatal recipients might obviate HAR due to the relative lack of XNA. Six neonatal lambs at 3 days (n=3) or 7 days (n=3) of life, and two fetal lambs at 125 and 142 days of gestation (term = 145 days) received cardiac grafts from adult Wistar-Furth (275-350 g) rats. All eight cardiac xenografts showed clinical evidence of HAR, with rapid swelling, loss of contractility, and ecchymosis and a mean survival time of 12.5 +/- 6.4 min. Sections of explanted grafts showed classical histologic features of HAR, including interstitial hemorrhages, platelet microthrombi, and edema, without leukocyte infiltration. Immunopathology of grafts harvested from fetal recipients showed a lack of significant intragraft deposition of sheep IgM, IgG, or C1q, but widespread endothelial labeling for C3, factor B, and properdin. In contrast, grafts in neonatal recipients showed IgM, IgG, and C1q deposition, as well as C3, factor B, properdin, and terminal complement (C) components. Fibrin deposition and platelet thrombi were seen in both groups of recipients. Injection of cobra venom factor resulted in prolongation of cardiac xenograft survival in neonatal lambs (n=3) to 12 hr. Analysis by immunohistology showed that normal sera from neonatal and adult, but not fetal, sheep contained IgM and IgG XNA reactive with rat cells. In conclusion, rodent grafts transplanted into fetal sheep undergo HAR, likely through direct activation of the alternate pathway of C, whereas neonatal lambs acquire XNA in the very early postnatal period and reject rat hearts through activation of both the classical and alternate pathways of C. Thus, at least in some species combinations, cardiac transplantation during the early postnatal period, or even in utero, may still be subject to development of HAR.

TH1 and TH2 lymphocytes in autoimmunity.

Summary: Xenotransplantation of non‐human organs into human recipients has long been proposed as a possible strategy to overcome the acute shortage of donor organs. However, vascular organ transplants to humans from phylogenetically disparate species such as the pig are not currently possible due to a rapid rejection process termed hyperacute rejection. This process is initiated by the binding of host pre‐formed ‘natural antibodies’ to the donor vascular endothelium, activation of the host complement system and activation or injury of the donor endothelial cells, leading to intravascular coagulation and loss of the graft due to ischaemic necrosis within minutes to hours of engraftment. Prevention of natural antibody binding and complement activation is viewed as paramount to preventing hyperacute rejection. Even if hyperacute rejection can be prevented, further barriers to successful discordant xenografts such as delayed xenograft rejection and a donor‐directed cell‐mediated rejection process will still represent major obstacles. This review examines recent advances being made in the various areas of xenograft research and the potential clinical application of pig‐to‐human xenografts that these strategies may bring.

Identification of Receptors Belonging to the Ig and C-Type Lectin Superfamilies on NK Cells and Their Functional Significance

Recognition of target cells by natural killer (NK) cells has been investigated using numerous approaches, but to date a clear understanding of the way(s) in which these effector cells interact with susceptible and nonsusceptible target cells or normal cells has not emerged. However, using the tools provided by molecular biological and monoclonal antibody technologies, a number of candidate receptor families have recently been identified. These families of receptors represent disparate molecular species, including both Type I and Type II glycoproteins and members of the Ig- and C-type lectin superfamilies. Even more interestingly, some of these receptors mediate activation of NK cells and others mediate inactivation of NK cells. Based on these recent developments, we may now be approaching an understanding of how and why NK cells may recognize and destroy some target cells, and how and why other cells may be resistant to lysis by NK cells.

A membrane cofactor protein transgenic mouse model for the study of discordant xenograft rejection.

In recent years, interest has been revived in the possibility of transplanting organs into humans from a phylogenetically disparate species such as the pig (xenotransplantation). Such discordant xenografts, however, are subject to hyperacute rejection (HAR) and activation of host complement plays a major role in this rejection. This problem may be solved through the use of transgenic technology by providing the grafted tissue with molecules that down-regulate the action of host complement. Transgenesis with a yeast artificial chromosome (YAC) was used to produce transgenic mice with the complete genomic gene of the human complement regulator membrane cofactor protein (MCP). Transgenic mice were obtained that exhibit full regulation of MCP as normally observed in humans. Hearts from these mice were shown to be significantly protected from HAR caused by human serum in an in vivo experimental procedure. We conclude that MCP can protect discordant xenografts from HAR caused by human serum and that transgenic mice can be used effectively as in vivo models for the study of the role of human complement regulatory molecules in xenotransplantation.

Cardiac xenografts between primate species provide evidence for the importance of the alpha-galactosyl determinant in hyperacute rejection.

Transplants performed between phylogenetically disparate species are subject to hyperacute rejection initiated by binding of xenoreactive natural Abs to endothelium in the donor organ. Binding of these Abs activates complement, leading to tissue injury and destruction of the graft. Human xenoreactive natural Abs recognize Gal alpha 1-3Gal beta 1-4GlcNAc (galactose alpha 1-3galactose beta 1-4-N-acetylglucosame); however, the relative importance of this Ag in graft rejection has not been proved. The present study was conducted to test the potential importance of alpha-galactosyl (alpha-Gal) determinants in the pathogenesis of hyperacute rejection. To this end, hearts (n = 3) from New World monkeys (Saimiri scureus, squirrel monkey), which can synthesize Gal alpha 1-3Gal, were transplanted heterotopically into Old World monkeys (Papio species, baboon), which do not synthesize Gal alpha 1-3Gal determinants and which have circulating anti-alpha Gal Abs. The xenografts were rejected in 51 to 56 min (mean +/- SD = 53.3 +/- 2.5), results similar to those observed in porcine grafts transplanted into baboons. Histologic analysis of the hearts revealed thrombosis and intraparenchymal hemorrhage and immune deposits consisting of IgM, Clq, C3, C4, C5b, and the membrane attack complex, but not properdin or factor B of the recipient deposited on graft endothelium. Sera obtained from baboons after perfusion of squirrel monkey kidneys revealed depletion of alpha-Gal-specific Abs and anti-pig endothelial cell Abs. These findings provide strong evidence that the Abs that accumulate in New World monkey organs during perfusion with baboon blood are the same Abs that would accumulate in a porcine organ transplanted into a primate and suggest that hyperacute rejection is not necessarily a reflection of phylogenetic distance but that the expression of terminal alpha-Gal residues provides an adequate target to initiate that process.

Homogentisic acid is the primary precursor of melanin synthesis in Vibrio cholerae, a Hyphomonas strain, and Shewanella colwelliana

The enzyme p-hydroxyphenylpyruvate hydroxylase (HPPH) is involved in pigmentation (pyomelanin) via homogentisic acid (HGA). Pyomelanin formation is correlated with HGA production and expression of HPPH in three disparate marine species: Vibrio cholerae, a Hyphomonas strain, and Shewanella colwelliana. Induction of pigmentation in V. cholerae 569B by nutrient limitation also correlated with production of HGA.

The emergence of xenotransplantation

The field of transplantation is faced with a growing shortage of human organs as the list of potential recipients continues to increase. Those currently listed can already expect long waits; some die waiting. Xenotransplantation is a potential solution to this widening donor-recipient disparity. Consequently, in recent years, there have been several clinical attempts using organs from nonhuman primates and pigs. The results with nonhuman primates as donors have been encouraging, but it is unlikely that these species will provide a long-term solution to the organ shortage. Most recent xenotransplantation research has therefore shifted to more phylogenetically disparate species, such as pigs, as potential donors. The major barrier to transplantation between members of disparate species combinations has been hyperacute rejection (HAR). The elements of humoral immunity involved in this rejection process include (1) naturally occurring antibodies directed against carbohydrate and other antigen expressed on pig endothelium, and (2) the complement system, which is activated by binding of natural antibodies to their targets. Several elegant strategies to prevent HAR are being developed. The creation of transgenic pigs, whose cells express human regulators of complement activation, is one such strategy. Another promising approach has been to remove antidonor antibodies from the recipient by absorption with some recently characterized carbohydrate epitopes of porcine endothelial xenoantigens. Recent experimental work indicates that HAR can successfully be prevented by inhibition or depletion of complement. A delayed type of xenograft rejection, characterized by endothelial cell antibody deposition and cellular infiltration, occurs over the next three to four days. The likely mechanisms involved in delayed xenograft rejection include antibody-dependent cell-mediated cytotoxicity and the phenomenon of endothelial cell activation.

Absence of naturally occurring hybridization between the quagga mussel (Dreissena bugensis) and the zebra mussel (D. polymorpha) in the lower Great Lakes

The coexistence of two dreissenids, the quagga mussel (Dreissena bugensis) and the zebra mussel (D. polymorpha), in a new environment raises the possibility of natural hybridization and possible introgression. Animals of both species were collected in areas where they occur sympatrically (25–39% were quagga mussels) and screened at two protein-coding loci believed to differentiate between the two species. The occurrence of alleles diagnostic for both species in an individual would demonstrate hybridization between the species. No hybrid individuals were observed in a survey of 750 animals from four sites in Lake Ontario and one site in Lake Erie. Successful hybridization between these two genetically disparate species seems unlikely in the Great Lakes.

Removal Of Baboon And Human Antiporcine Igg And Igm Natural Antibodies By Immunoadsorption

The safe and effective removal of xenoreactive antibodies in the peritransplant period is likely to be critical for the clinical application of xenotransplantation involving disparate donor species, such as the pig. In an effort to develop an improved method for antibody removal in xenotransplantation, we have studied reusable antihuman antibody (Ig) columns in vitro and in vivo. Two types of columns were tested: (1) an antihuman Ig column containing polyclonal sheep antihuman IgG (heavy- and light-chain-specific) conjugated to sepharose CL-4B (Ig-Therasorb), and (2) an antihuman Ig column using polyclonal antihuman IgM (mu-chain-specific) conjugated to sepharose. Passage of human or baboon plasma through the Ig-Therasorb column resulted in 97.5% and 78.4% mean reductions in total IgG and IgM, respectively. Reductions in total IgG and IgM correlated with lowering of antipig IgG (54-486 fold) and IgM (9-54 fold) antibody titers as assessed by pig endothelial cell ELISA. The ability of the Ig-Therasorb to significantly reduce IgM may be attributed to the light chain specificity of this column. With the anti-IgM column, marked reductions in total (82.6-83.9%) and antipig (27-54 fold) IgM in human and baboon plasma occurred, while levels of total and xenoreactive IgG were slightly affected. Other than a dilutional effect, neither column resulted in significant reduction in albumin, fibrinogen, factor 5, and factor 8. Repeated in vivo use of either column in baboons achieved reductions in IgG and IgM that closely followed the results of our in vitro studies. No subject morbidity or mortality occurred. Use of the Ig-Therasorb column with immunosuppression in two baboons receiving pig renal xenografts achieved sustained reductions in antipig antibodies and prevented hyperacute rejection. Subjects were sacrificed at 11 and 13 days posttransplant with functioning xenografts and were found to have no evidence of vascular xenograft rejection. We conclude that anti-Ig columns represent a safe and effective method for antibody removal, without several of the limitations of other antibody removal techniques. Also, columns appear to be safe for repeated antibody removal in the posttransplant period.

Specific tolerance across a discordant xenogeneic transplantation barrier.

Successful induction of tolerance across disparate (discordant) species barriers could overcome the organ shortage that presently limits clinical transplantation. We demonstrate here that xenogeneic swine thymic transplants can induce tolerance to swine antigens in mice, while positively selecting functional host CD4+ T cells. Immunologically normal C57BL/10 mice were thymectomized and depleted of T and natural killer cells; then they received transplants of fetal pig thymus and liver fragments. Mature mouse CD4+ T cells developed in the pig thymus grafts and migrated to the periphery. Swine grafts grew markedly and no anti-pig IgG response was produced. Mixed lymphocyte reactions confirmed that the new T cells were functional and were tolerant to pig antigens.

Evidence that rat xenoreactive antibodies recognize multiple protein antigens on guinea pig endothelial cells and platelets.

Xenoreactive antibodies are an integral part of the natural immune barrier to successful xenotransplantation between phylogenetically disparate species. Studies in primates suggest that the critical targets involved in hyperacute rejection of pig organs are glycoproteins expressed on endothelial cells and platelets. However, there is little information regarding the targets of xenoreactive antibodies and their cellular distribution in other experimental models of hyperacute xenograft rejection, including the commonly used guinea pig-to-rat model. The aim of this study was to characterize the target antigens on guinea pig platelets and endothelial cells that are recognized by rat anti-guinea pig antibodies. Using guinea pig platelet membrane proteins or intact guinea pig endothelial cells as antigens in an ELISA, we demonstrated that rat serum contains IgG* and IgM anti-guinea pig antibodies; levels of antiplatelet antibodies correlated with those against endothelial cells. Serum from naive or complement-depleted rats transplanted with a guinea pig heart was investigated by immunoblotting against membrane proteins extracted from guinea pig platelets and endothelial cells. Normal rat serum revealed numerous bands on either platelet or endothelial cell immunoblots, without obvious similarities in banding pattern under reduced or nonreduced conditions. Absorption of rat serum with intact guinea pig endothelial cells reduced reactivity against numerous bands on endothelial cell membrane blots, but only partially reduced reactivity with three platelet bands (141, 155, and 210 kDa). Absorption of rat serum with intact guinea pig platelets resulted in reduction in reactivity against both platelet and endothelial cell immunoblots. Antibodies eluted from those intact guinea pig endothelial cells and platelets used to absorb rat sera were found to yield patterns of membrane blot reactivity similar to those with unabsorbed sera, suggesting that the proteins recognized are expressed on the cell surface. Lectin affinity blotting demonstrated many of the guinea pig endothelial cell and platelet membrane proteins to be glycosylated. However, digestion of endothelial cell and platelet immunoblots with a mixture of glycosidases failed to change the xenoreactivity with naive rat serum. Immunoblot analysis of serum samples taken daily from complement-depleted rats carrying a functioning guinea pig heart for 3-4 days showed an increase in intensity for specific protein bands on platelets (38, 48, 56, 141, and 155 kDa) and endothelial cells (30, 210, and 270 kDa); no new protein bands were observed. Increased reactivity at several bands correlated with highly elevated rat serum anti-guinea pig antibody titers, as determined by ELISA.(ABSTRACT TRUNCATED AT 400 WORDS)

Immunoelectrophoretic characterization and cross‐reactivity of Rochalimaea henselae, Rochalimaea quintana and Afipia felis

The soluble antigens of Rochalimaea henselae, Rochalimaea quintana and Afipia felis were characterized by crossed immunoelectrophoresis using bacterial sonicates as antigens against pooled hyperimmune rabbit sera. A precipitin pattern was drawn for each bacterium and shown to be reproducible and stable even when normal or preimmune rabbit serum was incorporated in the intermediate gel. By this technique 56 antigens were identified from R. henselae, 49 from R. quintana, and 39 from A. felis. The serological cross-reaction between R. henselae, R. quintana and A. felis, and between these 3 bacteria and 32 pathogenic bacteria was analysed by rocket-line immunoelectrophoresis, crossed-line immunoelectrophoresis, and tandem-crossed electrophoresis. It was concluded that (i) 4-7 antigens distinguish R. henselae, R. quintana and A. felis from each other, (ii) both Gram-positive and Gram-negative bacteria cross-react with R. henselae, R. quintana and A. felis antisera, (iii) the cross-reacting antigens of Gram-negative bacteria have both precipitating and non-precipitating specificities, whereas Gram-positive bacteria have mainly non-precipitating specificities, (iv) the cross-reacting antigens are common to several species, and (v) fewer cross-reacting antigens are found in phylogenetically disparate species than in more closely related species.

Sex determination in the Hymenoptera: a review of models and evidence

The haploid males and diploid females of Hymenoptera have all chromosomes in the same proportions. This rules out most familiar sex-determining mechanisms, which rely on dosage differences at sex determination loci. Two types of model — genie balance and complementary sex determination (CSD) — have been invoked for Hymenoptera. Experimental studies provide no good evidence for genie balance models, which are contradicted by the detection of diploid males in 33 disparate species. Furthermore, recent advances have shown that sex determination in the best-studied diploid animals does not depend on genie balance, removing the original justification for hymenopteran genie balance models. Instead, several Hymenoptera have single-locus CSD. In this system, sex locus heterozyotes are female while homozygotes and hemizygotes are male. Single-locus CSD does not apply to several inbreeding species and this probably reflects selection against the regular production of diploid males, which are sterile. A multilocus CSD model, in which heterozygosity at any one of several sex loci leads to female development has also been proposed. To date, multilocus CSD has not been demonstrated but several biases against its detection must be considered. CSD can apply to thelytokous races as long as the cytogenetic mechanism permits retention of sex locus heterozygosity. However, some thelytokous races clearly do not have CSD. The distribution of species with and without CSD suggests that this form of sex determination may be ancestral in the Hymenoptera. However, phylogenetic analyses are hindered by the lack of data from several superfamilies and the fact that the internal phylogeny of the Hymenoptera remains controversial.

Surfactant protein A-binding proteins. Characterization and structures.

An alveolar cell membrane protein acts as a surfactant protein A (SP-A) receptor; it binds SP-A and regulates surfactant secretion. We identified such alveolar cell membrane SP-A-binding proteins using anti-idiotype antibodies directed against the surfactant protein binding region of anti-surfactant antibodies. These monoclonal anti-idiotype antibodies, A2C and A2R, also recognize an alveolar cell membrane protein of approximately 30 kDa. A pulmonary protein of approximately 30 kDa binds SP-A. Unique cDNAs encoding this protein were identified in human (4.1-kilobase) and porcine (1.8-kilobase) lung expression libraries. Coding regions of these cDNAs cross-hybridize with each other under stringent conditions. Both cDNAs encode similar approximately 32-kDa proteins that bind SP-A. The human and porcine SP-A recognition (SPAR) proteins resemble each other, as well as other cell membrane receptors. Their projected structures are consistent with cell membrane receptors. Recombinant human and porcine SPAR proteins bind SP-A as well as the two anti-idiotype antibodies just as do native lung proteins of approximately 30 kDa. SPAR transcripts are expressed primarily in lung. The cellular distribution of these transcripts, as determined by in situ hybridization, is similar to that of SPAR protein, as determined by immunohistochemistry; both are found in cells consistent with type II pneumocytes. SPAR-producing cells resemble the alveolar cells expressing SP-B and SP-C transcripts in appearance, location, and distribution. Therefore, cDNAs for pulmonary SP-A-binding proteins from two disparate species have been isolated and sequenced, and the recombinant proteins they encode bind the same ligand. Further structural, functional, and genetic studies of these proteins may help explain how pulmonary surfactant secretion is regulated.

Effect of Xenogeneic Chimerism in a Human/Sheep Model on Natural Antibody

Xenogeneic transplantation is a potential solution to the severe shortage of donor organs for clinical transplantation. The primary limitation to xenogeneic transplantation between widely disparate species is hyperacute rejection, which is triggered by the recipient's natural antibodies reacting against the donor's endothelial cells. Natural antibodies react between widely disparate species but do not react between closely related species. Specific tolerance for xenogeneic transplantation between closely related species can be induced by creating hematopoietic chimerism between donor and recipient. However, whether specific xenograft tolerance can be induced by the creation of chimerism between widely disparate species, where natural antibody reacts, is unknown. We previously have established a model of hematopoietic chimerism between widely disparate species by the in utero transplantation of human fetal hematopoietic stem cells into early gestation fetal lambs. In the present study, we determined whether long-standing hematopoietic chimerism in this human/sheep model reduces the level of natural antibody directed against human endothelial cells. To answer this question, we measured the reactivity of serum from five chimeric sheep, five sheep controls, and five human controls in an in vitro enzymelinked immunoabsorbance assay directed against human umbilical vein endothelial cells. Unexpectedly, we found that long-standing hematopoietic chimerism in the human/sheep model did not reduce the reactivity of serum against human endothelial cells compared to age-matched sheep controls. These results suggest that the induction of hematopoietic chimerism between widely disparate species will not control the problem of natural antibody and hyperacute rejection.

Evidence that polyreactive antibodies are deposited in rejected discordant xenografts.

The rejection of organs transplanted between phylogenetically disparate species is thought to be initiated by the binding of naturally occurring antibodies of the recipient to the endothelium lining the blood vessels of the donor organ. We recently showed that among the xenoreactive natural antibodies in human serum that react with porcine endothelial cells and endothelial cell--derived glycoproteins are polyreactive antibodies. To test whether polyreactive natural antibodies are present in rejected xenografts we developed a series of hybridoma-derived antibodies specific for the polyreactive human monoclonal antibody 103, which we have shown to bind efficiently to porcine endothelial cells. Using these antiidiotypic reagents we detected antibodies bearing the 103 idiotype in a panel of human sera and on the surface of lymphocytes in the spleen of humans, rhesus monkeys, and baboons. The antiidiotypic reagents reacted in a pattern similar to the distribution of IgM, with immunoglobulin deposits in tissues obtained from pig-to-rhesus monkey and pig-to-baboon xenografts. Analysis of immunoglobulin eluted from these sites showed that they antibodies display the antigen-binding features of natural antibodies. Our findings are consistent with the hypothesis that idiotypes of polyreactive natural antibodies are broadly crossreactive. They also suggest that the polyreactive and xenoreactive IgM, which have been detected based on in vitro assays, may be deposited in a xenogeneic organ graft.

The Pathogenesis of Hyperacute Xenograft Rejection

A critical shortage of donor organs has driven many in the transplantation community to consider the use of animals as organ donors for humans, that is, xenotransplantation. While successful xenotransplantation of primate kidneys was achieved 25 years ago, most now advocate use of non primates as donors because of the risk of disease transmission and ethical concerns attendant to the use of primates. The major hurdle to xenotransplantation of organs between phylogenetically disparate species is the hyperacute rejection reaction that invariably destroys organ xenografts placed in unmodified recipients. Here we review recent insights concerning the pathogenesis of hyperacute rejection reactions. We focus particular attention on the endothelial cell, which serves not only as the target of xenoreactive antibodies and complement, but also, as a consequence of endothelial cell activation, as an instrument of tissue injury. We discuss a phenomenon called “accommodation” in which an organ graft acquires resistance to humoral-mediated injury.