“Catastrophic‐selection” is an evolutionary mechanism, by which entire parental‐populations are eliminated but very few mutated offspring survive and replace extinct parental‐populations. The human ...natural anti‐carbohydrate antibodies, anti‐Gal and anti‐Neu5Gc suggest the occurrence of catastrophic‐selection events in primate evolution. Parental‐populations synthesizing corresponding carbohydrate‐antigens underwent extinction in viral epidemics, and few offspring survived. These offspring carried accidental mutations that inactivated carbohydrate‐antigen synthesis and produced natural‐antibody against the lost antigen. Such natural anti‐carbohydrate antibody was produced against environmental carbohydrate‐antigens (e.g., gastrointestinal bacteria). The carbohydrate‐antigen in infected parental‐populations was also synthesized on viruses by the host glycosylation‐machinery. The natural‐antibody in the offspring bound to the carbohydrate‐antigen on infecting viruses produced in parental‐populations, destroyed the viruses and protected these offspring from extinction. This process occurred in ancestral Old‐World monkeys and apes synthesizing α‐gal epitopes, which were replaced 20–30 million‐years‐ago by offspring lacking α‐gal epitopes and producing natural anti‐Gal antibody against this antigen, and later in hominins synthesizing the sialic‐acid antigen Neu5Gc, which were replaced by offspring lacking Neu5Gc and producing anti‐Neu5Gc antibody. A present‐day example for accidental mutations in very few humans that lost a common carbohydrate‐antigen and produce a natural antibody against it is the rare blood‐group “Bombay” individuals. These individuals lack the H‐antigen (blood‐group O) which is synthesized in all other humans, and produce the natural anti‐H antibody against blood‐group O. Overall, it is suggested that natural anti‐carbohydrate antibodies played a critical role in preventing complete extinction of mammalian species in epidemics of highly virulent viruses and may have similar role in future events.
The description of "serum sickness" more than a century ago in humans transfused with animal sera eventually led to identification of a class of human antibodies directed against glycans terminating ...in the common mammalian sialic acid
Glycolylneuraminic acid (Neu5Gc), hereafter called "Neu5Gc-glycans." The detection of such glycans in malignant and fetal human tissues initially raised the possibility that it was an oncofetal antigen. However, "serum sickness" antibodies were also noted in various human disease states. These findings spurred further research on Neu5Gc, and the discovery that it is not synthesized in the human body due to a human-lineage specific genetic mutation in the enzyme
. However, with more sensitive techniques Neu5Gc-glycans were detected in smaller quantities on certain human cell types, particularly epithelia and endothelia. The likely explanation is metabolic incorporation of Neu5Gc from dietary sources, especially red meat of mammalian origin. This incorporated Neu5Gc on glycans appears to be the first example of a "xeno-autoantigen," against which varying levels of "xeno-autoantibodies" are present in all humans. The resulting chronic inflammation or "xenosialitis" may have important implications in human health and disease, especially in conditions known to be aggravated by consumption of red meat. In this review, we will cover the early history of the discovery of "serum sickness" antibodies, the subsequent recognition that they were partly directed against Neu5Gc-glycans, the discovery of the genetic defect eliminating Neu5Gc production in humans, and the later recognition that this was not an oncofetal antigen but the first example of a "xeno-autoantigen." Further, we will present comments about implications for disease risks associated with red meat consumption such as cancer and atherosclerosis. We will also mention the potential utility of these anti-Neu5Gc-glycan antibodies in cancer immunotherapy and provide some suggestions and perspectives for the future. Other reviews in this special issue cover many other aspects of this unusual pathological process, for which there appears to be no other described precedent.
Two human natural anti‐carbohydrate antibodies appeared in critical evolutionary events that brought primates and hominins to brink of extinction. The first is the anti‐Gal antibody, produced in ...Old‐World monkeys (OWM), apes and humans. It binds the carbohydrate‐antigen ‘α‐gal epitope’ (Galα1‐3Galβ1‐4GlcNAc‐R) on carbohydrate‐chains (glycans) synthesized by non‐primate mammals, lemurs and New‐World monkeys (NWM). The second is anti‐N‐glycolylneuraminic‐acid (anti‐Neu5Gc) antibody binding Neu5Gc on glycans synthesized by OWM, apes and most non‐primate mammals. Ancestral OWM and apes synthesized α‐gal epitopes and were eliminated ~20–30 million‐years‐ago (mya). Only few accidentally mutated offspring lacking α‐gal epitopes, produced anti‐Gal and survived. Hominin‐populations living ~3 mya synthesized Neu5Gc and were eliminated, but few mutated offspring that accidently lost their ability to synthesize Neu5Gc, produced natural anti‐Neu5Gc antibody. These hominins survived and ultimately evolved into present‐day humans. It is argued that these two near‐extinction events were likely to be the result of epidemics caused by highly virulent and lethal enveloped viruses that killed parental‐populations. These viruses presented α‐gal epitopes or Neu5Gc synthesized in host‐cells of the parental‐populations. Mutated offspring survived the epidemics because they were protected from the lethal virus by the natural anti‐Gal or anti‐Neu5Gc antibodies they produced due to loss of immune‐tolerance to α‐gal epitopes or to Neu5Gc, respectively.
In the suggested evolutionary scenario, ancestral Old‐World monkeys (OWM) and apes synthesized α‐gal epitopes (α‐gal+) and lacked the anti‐Gal antibody, similar to non‐primate mammals, lemurs and New‐World monkeys (NWM). Accidental mutations in the α1,3GT gene GGTA1 of few ancestral OWM and apes resulted in loss of the α‐gal epitope (α‐gal‐) and inadvertent production of natural anti‐Gal antibody. An epidemic of a highly virulent and lethal virus eliminated ancestral OWM and apes synthesizing α‐gal epitopes, but the mutated progeny producing anti‐Gal were protected against the virus which presented α‐gal epitopes that were synthesized in host‐cells of the parental α‐gal+ primates.
Humans cannot synthesize N‐glycolylneuraminic acid (Neu5Gc) but dietary Neu5Gc can be absorbed and deposited on endothelial cells (ECs) and diet‐induced anti‐Neu5Gc antibodies (Abs) develop early in ...human life. While the interaction of Neu5Gc and diet‐induced anti‐Neu5Gc Abs occurs in all normal individuals, endothelium activation by elicited anti‐Neu5Gc Abs following a challenge with animal‐derived materials, such as following xenotransplantation, had been postulated. Ten primary human EC preparations were cultured with affinity‐purified anti‐Neu5Gc Abs from human sera obtained before or after exposure to Neu5Gc‐glycosylated rabbit IgGs (elicited Abs). RNAs of each EC preparation stimulated in various conditions by purified Abs were exhaustively sequenced. EC transcriptomic patterns induced by elicited anti‐Neu5Gc Abs, compared with pre‐existing ones, were analyzed. qPCR, cytokines/chemokines release, and apoptosis were tested on some EC preparations. The data showed that anti‐Neu5Gc Abs induced 967 differentially expressed (DE) genes. Most DE genes are shared following EC activation by pre‐existing or anti‐human T‐cell globulin (ATG)‐elicited anti‐Neu5Gc Abs. Compared with pre‐existing anti‐Neu5Gc Abs, which are normal component of ECs environment, elicited anti‐Neu5Gc Abs down‐regulated 66 genes, including master genes of EC function. Furthermore, elicited anti‐Neu5Gc Abs combined with complement‐containing serum down‐regulated most transcripts mobilized by serum alone. Both types of anti‐Neu5Gc Abs‐induced a dose‐ and complement‐dependent release of selected cytokines and chemokines. Altogether, these data show that, compared with pre‐existing anti‐Neu5Gc Abs, ATG‐elicited anti‐Neu5Gc Abs specifically modulate genes related to cytokine responses, MAPkinase cascades, chemotaxis, and integrins and do not skew the EC transcriptome toward a pro‐inflammatory profile in vitro.
Human beings do not synthesize the glycolyl form of the sialic acid (Neu5Gc) and only express the acetylated form of the sugar, whereas a diet‐based intake of Neu5Gc provokes a natural immunization ...and production of anti‐Neu5Gc antibodies in human serum. However, Neu5Gc is expressed on mammal glycoproteins and glycolipids in most organs and cells. We review here the relevance of Neu5Gc and anti‐Neu5Gc antibodies in the context of xenotransplantation and the use of animal‐derived molecules and products, as well as the possible consequences of a long‐term exposure to anti‐Neu5Gc antibodies in recipients of xenografts. In addition, the importance of an accurate estimation of the anti‐Neu5Gc response following xenotransplantation and the future contribution of knockout animals mimicking the human situation are also assessed.
Numerous molecules have been considered as targets for cancer immunotherapy because of their levels of expression on tumor cells, their putative importance for tumor biology, and relative ...immunogenicity. In this review we focus on the ganglioside GM3(Neu5Gc), a glycosphingolipid present on the outer side of the plasma membrane of vertebrate cells. The reasons for selecting GM3(Neu5Gc) as a tumor-specific antigen and its use as a target for cancer immunotherapy are discussed, together with the development of antitumor therapies focused on this target by the Center of Molecular Immunology (CIM, Cuba).
The glycans on enveloped viruses are synthesized by host-cell machinery. Some of these glycans on zoonotic viruses of mammalian reservoirs are recognized by human natural antibodies that may protect ...against such viruses. These antibodies are produced mostly against carbohydrate antigens on gastrointestinal bacteria and fortuitously, they bind to carbohydrate antigens synthesized in other mammals, neutralize and destroy viruses presenting these antigens. Two such antibodies are: anti-Gal binding to α-gal epitopes synthesized in non-primate mammals, lemurs, and New World monkeys, and anti-N-glycolyl neuraminic acid (anti-Neu5Gc) binding to N-glycolyl-neuraminic acid (Neu5Gc) synthesized in apes, Old World monkeys, and many non-primate mammals. Anti-Gal appeared in Old World primates following accidental inactivation of the α1,3galactosyltransferase gene 20–30 million years ago. Anti-Neu5Gc appeared in hominins following the inactivation of the cytidine-monophosphate-N-acetyl-neuraminic acid hydroxylase gene, which led to the loss of Neu5Gc <6 million-years-ago. It is suggested that an epidemic of a lethal virus eliminated ancestral Old World-primates synthesizing α-gal epitopes, whereas few mutated offspring lacking α-gal epitopes and producing anti-Gal survived because anti-Gal destroyed viruses presenting α-gal epitopes, following replication in parental populations. Similarly, anti-Neu5Gc protected few mutated hominins lacking Neu5Gc in lethal virus epidemics that eliminated parental hominins synthesizing Neu5Gc. Since α-gal epitopes are presented on many zoonotic viruses it is suggested that vaccines elevating anti-Gal titers may be of protective significance in areas endemic for such zoonotic viruses. This protection would be during the non-primate mammal to human virus transmission, but not in subsequent human to human transmission where the virus presents human glycans. In addition, production of viral vaccines presenting multiple α-gal epitopes increases their immunogenicity because of effective anti-Gal-mediated targeting of vaccines to antigen presenting cells for extensive uptake of the vaccine by these cells.
The glycocalyx of human cells differs from that of many other mammals by the lack of the sialic acid N-glycolylneuraminic acid (Neu5Gc) and increased abundance of its precursor N-acetylneuraminic ...acid (Neu5Ac). Most humans also have circulating antibodies specifically targeting the non-human sialic acid Neu5Gc. Recently, several additional mammalian species have been found to also lack Neu5Gc. In all cases, loss-of-function mutations in the gene encoding the sialic acid-modifying enzyme CMAH are responsible for the drastic change in these species. Unlike other glycan antigens, Neu5Gc apparently cannot be produced by microbes, raising the question about the origin of these antibodies in humans. Dietary exposure and presentation on bacteria coating themselves with Neu5Gc from the diet are distinct possibilities. However, the majority of the non-human species that lack Neu5Gc do not consume diets rich in Neu5Gc, making it unlikely that they will have been immunized against this sialic acid. A notable exception are mustelids (ferrets, martens and their relatives) known for preying on various small mammal species rich in Neu5Gc. No studies exist on levels of anti-Neu5Gc antibodies in non-human species. Evolutionary scenarios for the repeated, independent fixation of
loss-of-function mutations at various time points in the past include strong selection by parasites, especially enveloped viruses, stochastic effects of genetic drift, and directional selection via female immunity to paternal Neu5Gc. Convergent evolution of losses of the vertebrate-specific self-glycan Neu5Gc are puzzling and may represent a prominent way in which glycans become agents of evolutionary change in their own right. Such change may include the reconfiguration of innate immune lectins that use self-sialic acids as recognition patterns.
Sialic acids are common monosaccharides that are widely expressed as outer terminal units on all vertebrate cell surfaces, and play fundamental roles in cell-cell and cell-microenvironment ...interactions. The predominant sialic acids on most mammalian cells are N-glycolylneuraminic acid (Neu5Gc) and N-acetylneuraminic acid (Neu5Ac). Neu5Gc is notable for its deficiency in humans due to a species-specific and species-universal inactivating deletion in the CMAH gene encoding the hydroxylase that converts CMP-Neu5Ac to CMP-Neu5Gc. However, Neu5Gc is metabolically incorporated into human tissues from dietary sources (particularly red meat), and detected at even higher levels in some human cancers. Early life exposure to Neu5Gc-containing foods in the presence of certain commensal bacteria that incorporate dietary Neu5Gc into lipooligosaccharides can lead to generation of antibodies that are also cross-reactive against Neu5Gc-containing glycans in human tissues ("xeno-autoantigens"). Such anti-Neu5Gc "xeno-autoantibodies" are found in all humans, although ranging widely in levels among individuals, and displaying diverse and variable specificities for the underlying glycan. Experimental evidence in a human-like Neu5Gc-deficient Cmah(-) (/) (-) mouse model shows that inflammation due to "xenosialitis" caused by this antigen-antibody interaction can promote tumor progression, suggesting a likely mechanism for the well-known epidemiological link between red meat consumption and carcinoma risk. In this review, we discuss the history of this field, mechanisms of Neu5Gc incorporation into tissues, the origin and specificities of human anti-Neu5Gc antibodies, their use as possible cancer biomarkers, implications of xenosialitis in cancer initiation and progression, and current and future approaches toward immunotherapy that could take advantage of this unusual human-specific phenomenon.
Previous studies have demonstrated that Neu5Gc is highly expressed in breast, ovarian, prostate, colon and lung cancers, but not in normal human cells. The presence of Neu5Gc is important for ...prognosis and is associated with aggressiveness, metastasis, and tumor grade. However, increased Neu5Gc in bladder cancer remains unclear. LIP from lamprey binds the carbohydrate receptor of N-glycolylneuraminic acid (Neu5Gc). The combination of Neu5Gc and LIP suggested that it might be used as a diagnostic tool for the detection of Neu5Gc tumor antigen. Here, the classical animal model of bladder cancer was successfully induced by MNU bladder perfusion. The ELISA results showed that the expression level of Neu5Gc in the urine of normal rats was 94.96 ± 21.01ng/mg, and that of bladder cancer rats was 158.28 ± 34.86 ng/mg. In addition, the results of SNA and LIP immunohistochemistry demonstrated the high expression of Neu5Gc in bladder cancer. After the addition of Neu5Gc to BIU-87 and SV-HUC-1 cells, transcriptomic sequencing and real-time quantitative PCR analysis demonstrated that the gene expression of Neu5Gc synthesis pathway was significantly increased. These data suggest that LIP provides a new tool for the detection of biological samples, especially urine from patients with bladder cancer or suspected cancer, and that revealing the mechanism of abnormal glycosylation can provide theoretical basis for clinical studies.
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•LIP from lamprey can recognize the glycosylation of N- glycolylneuraminic acid (Neu5Gc), and might be used as a diagnostic tool for detecting the expression of Neu5Gc.•The expression of Neu5Gc in urine of rats with bladder cancer increased significantly.•The progression of bladder cancer is related to synthesis and glycosylation related genes of Neu5Gc.
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