Carbohydrates borne on human glycophorin A are recognized by porcine Kupffer cells

The role of sialic acids in the immune recognition of xenografts

Presentation of sialic acid (Sia) varies among different tissues and organs within each species, and between species. This diversity has biologically important consequences regarding the recognition of cells by "xeno" antibodies (Neu5Gc vs Neu5Ac). Sia also plays a central role in inflammation by influencing binding of the asialoglycoprotein receptor 1 (ASGR-1), Siglec-1 (Sialoadhesin), and cellular interactions mediated by the selectin, integrin, and galectin receptor families. This review will focus on what is known about basic Sia structure and function in association with xenotransplantation, how changes in sialylation may occur in this context (through desialylation or changes in sialyltransferases), and how this fundamental pathway modulates adhesive and cell activation pathways that appear to be particularly crucial to homeostasis and inflammation for xenografts.

A human-specific mutation limits nonhuman primate efficacy in preclinical xenotransplantation studies

BACKGROUND

Patients diagnosed with fulminant hepatic failure face high mortality rates. A potential therapeutic approach for these patients is the use of extracorporeal porcine liver perfusion, to serve as a form of "liver dialysis." Previously, our laboratory has shown that, during a 72-hour extracorporeal perfusion with human blood, porcine Kupffer cells bind to and phagocytose human erythrocytes causing the hematocrit to fall to 2.5% of the original value. Subsequently, erythrocyte binding has been shown to involve N-acetylneuraminic acid (Neu5Ac) on the surface of human erythrocytes and sialoadhesin on the surface of the porcine Kupffer cells.

METHODS

Given that no primate other than the human is known to express the majority of its sialic acid as Neu5Ac, we evaluated whether nonhuman primates would provide adequate evaluation of the loss of erythrocytes that might be expected in a clinical trial of extracorporeal porcine liver perfusion.

RESULTS

We found that while porcine macrophages readily bound human erythrocytes, binding of nonhuman primate erythrocytes was significantly reduced (P<0.001).

CONCLUSIONS

This study suggests that nonhuman primates may fail to serve as an adequate model for studying extracorporeal porcine liver perfusion because of the fact that porcine macrophages do not bind nonhuman primate erythrocytes.

Porcine sialoadhesin: a newly identified xenogeneic innate immune receptor

Extracorporeal porcine liver perfusion is being developed as a bridge to liver allotransplantation for patients with fulminant hepatic failure. This strategy is limited by porcine Kupffer cell destruction of human erythrocytes, mediated by lectin binding of a sialic acid motif in the absence of antibody and complement. Sialoadhesin, a macrophage restricted lectin that binds sialic acid, was originally described as a sheep erythrocyte binding receptor. Given similarities between sialoadhesin and the unidentified macrophage lectin in our model, we hypothesized porcine sialoadhesin contributed to recognition of human erythrocytes. Two additional types of macrophages were identified to bind human erythrocytes-spleen and alveolar. Expression of sialoadhesin was confirmed by immunofluorescence in porcine tissues and by flow cytometry on primary macrophages. A stable transgenic cell line expressing porcine sialoadhesin (pSn CHO) bound human erythrocytes, while a sialoadhesin mutant cell line did not. Porcine macrophage and pSn CHO recognition of human erythrocytes was inhibited approximately 90% by an antiporcine sialoadhesin monoclonal antibody and by human erythrocyte glycoproteins. Furthermore, this binding was substantially reduced by sialidase treatment of erythrocytes. These data support the hypothesis that porcine sialoadhesin is a xenogeneic receptor that mediates porcine macrophage binding of human erythrocytes in a sialic acid-dependent manner.

Isolation of rat Kupffer cells by ex vivo perfusion and their primary culture

AIM: To explore a convenient and effective method for isolation and primary culture of rat Kupffer cells (KCs) in vitro.

METHODS: Ex vivo rat liver tissue was perfused with collagenase IV and diced into small pieces. The diced tissue was digested for 30 min at 37℃and centrifuged to remove hepatocytes. KCs were then separated by means of Percoll density gradient centrifugation and selective adherence. Phagocytosis assay and immunocytochemistry for ED2 were used to identify cells isolated.

RESULTS: The average cell yield per gram of liver before plastic adherence was (2.1 ± 0.3) × 10⁶, and (1.5 ± 0.1) × 10⁶following plastic adherence. The viability of KCs isolated was higher than 92% as determined by trypan blue exclusion. The purity of KCs, identified by immunocytochemistry for ED2, was higher than 90%. Cultured KCs were functionally intact and exhibited irregular shape.

CONCLUSION: The method for isolation and culture of Kupffer cells by ex vivo perfusion is convenient, efficient and stable. Cultured Kupffer cells retain naive biological characteristics and can be used in future studies.