N-linked oligosaccharides can protect target cells from the lysis mediated by NK cells but not by cytotoxic T lymphocytes: role of NKG2-A

Expression of placental glycans and its role in regulating peripheral blood NK cells during preeclampsia: a perspective

Preeclampsia is a pregnancy-related multisystem disorder characterized by altered trophoblast invasion, oxidative stress, exacerbation of systemic inflammatory response, and endothelial damage. The pathogenesis includes hypertension and mild-to-severe microangiopathy in the kidney, liver, placenta, and brain. The main mechanisms involved in its pathogenesis have been proposed to limit trophoblast invasion and increase the release of extracellular vesicles from the syncytiotrophoblast into the maternal circulation, exacerbating the systemic inflammatory response. The placenta expresses glycans as part of its development and maternal immune tolerance during gestation. The expression profile of glycans at the maternal-fetal interface may play a fundamental role in physiological pregnancy changes and disorders such as preeclampsia. It is unclear whether glycans and their lectin-like receptors are involved in the mechanisms of maternal-fetal recognition by immune cells during pregnancy homeostasis. The expression profile of glycans appears to be altered in hypertensive disorders of pregnancy, which could lead to alterations in the placental microenvironment and vascular endothelium in pregnancy conditions such as preeclampsia. Glycans with immunomodulatory properties at the maternal-fetal interface are altered in early-onset severe preeclampsia, implying that innate immune system components, such as NK cells, exacerbate the systemic inflammatory response observed in preeclampsia. In this article, we discuss the evidence for the role of glycans in gestational physiology and the perspective of glycobiology on the pathophysiology of hypertensive disorders in gestation.

Branched I antigen regulated cell susceptibility against natural killer cytotoxicity through its N-linked glycosylation and overall expression

Cell surface glycosylation has been known as an important modification process that can be targeted and manipulated by malignant cells to escape from host immunosurveillance. We previously showed that the blood group branched I antigen on the leukemia cell surface can regulate the cell susceptibility against natural killer (NK) cell-mediated cytotoxicity through interfering target-NK interaction. In this work, we first identified N-linkage as the major glycosylation linkage type for branched I glycan formation on leukemia cells, and this linkage was responsible for cell sensitivity against therapeutic NK-92MI targeting. Secondly, by examining different leukemia cell surface death receptors, we showed death receptor Fas had highest expressions in both Raji and TF-1a cells. Mutations on two Fas extracellular N-linkage sites (118 and 136) for glycosylation impaired activation of Fas-mediated apoptosis during NK-92MI cytotoxicity. Last, we found that the surface I antigen expression levels enable leukemia cells to respond differently against NK-92MI targeting. In low I antigen expressing K-562 cell, reduction of I antigen presence greatly reduced leukemia cell susceptibility against NK-92MI targeting. But in other high I antigen expressing leukemia cells, similar reduction in I antigen expression did not affect cell susceptibility.

Glycan expression in chorionic villi from histocultures of women with early-onset preeclampsia: Immunomodulatory effects on peripheral natural killer cells

New evidence suggests that glycan expression in placental cells of women with invasive disorders of pregnancy differs from that in normal pregnant women. Hypothesizing that modifications of glycan expression could account for the course of preeclampsia, we established placental villous histocultures and compared glycan expression in women with preeclampsia with that in normal pregnant women and also in syncytialized BeWo cells, and we tested the effect of glycan expression on the functional phenotypes of circulating natural killer (NK) cells. Histocultures of third-trimester placentae from women with preeclampsia and full-term placentae from healthy pregnant women and BeWo choriocarcinoma cells were assessed for the expression of terminal glycans by lectin-binding assays. Circulating NK cells from nonpregnant healthy donors were tested in vitro for their cytotoxic activity and intracellular cytokine content. Histocultures from women with preeclampsia expressed significantly more mannose than did those from healthy pregnant women. Both histocultures and BeWo cells expressed terminal fucose, mannose, sialic acid, and N -acetylgalactosamine, although mean fluorescence intensity (MFI) expression was lower in choriocarcinoma cells than in cells from histocultures. Cocultures of circulating NK cells with K562 target cells resulted in a dose-dependent cytotoxicity effect, but the use of BeWo cells as target reduced cytotoxic activity; this reduction was not affected by syncytialization. Histocultures of placental villous tissue of women with preeclampsia expressed high levels of terminal mannose. We proposethat placental glycans may modulate the functional activity of circulating NK cells in the context of systemic inflammatory response in preeclampsia.

Clustered carbohydrates as a target for natural killer cells: a model system

Membrane-associated oligosaccharides are known to take part in interactions between natural killer (NK) cells and their targets and modulate NK cell activity. A model system was therefore developed using synthetic glycoconjugates as tools to modify the carbohydrate pattern on NK target cell surfaces. NK cells were then assessed for function in response to synthetic glycoconjugates, using both cytolysis-associated caspase 6 activation measured by flow cytometry and IFN-gamma production. Lipophilic neoglycoconjugates were synthesized to provide their easy incorporation into the target cell membranes and to make carbohydrate residues available for cell-cell interactions. While incorporation was successful based on fluorescence monitoring, glycoconjugate incorporation did not evoke artifactual changes in surface antigen expression, and had no negative effect on cell viability. Glycoconjugates contained Le(x), sulfated Le(x), and Le(y) sharing the common structure motif trisaccharide Le(x) were revealed to enhance cytotoxicity mediated specifically by CD16 +CD56+NK cells. The glycoconjugate effects were dependent on saccharide presentation in a polymeric form. Only polymeric, or clustered, but not monomeric glycoconjugates resulted in alteration of cytotoxicity in our system, suggesting that appropriate presentation is critical for carbohydrate recognition and subsequent biological effects.

Thomsen-Friedenreich (T) antigen expression increases sensitivity of natural killer cell lysis of cancer cells

In this study, we demonstrate a correlation between T antigen expression on a panel of human carcinoma cell lines and their sensitivity to porcine NK cell lysis. Specifically, the more T antigen is expressed, the more sensitive the cancer cells are to porcine NK cell lysis. Furthermore, this correlation also exists for these cells and their ability to induce tumors in vivo. In this porcine animal model, the less T antigen is expressed, the more prolific the tumor growth in vivo and vice versa. Using the human colorectal adenocarcinoma cell line SW-48, we used limiting dilution to clone 2 populations of cells, one expressing high and the other low levels of T antigen, clones 143 and 111, respectively. In these cloned cells, the clone that expressed more T antigen was more NK-sensitive in vitro and weakly induced tumor growth in vivo. Inversely, the clone that expressed less T antigen clone was more NK-resistant in vitro and grew more prolific tumors in vivo. Using soluble T antigen in a competitive inhibition assay, there was a decrease in porcine NK cell killing of the T antigen+ human cell line Colo 320HSR. Taken together, these findings suggest a novel role for T antigen in the NK cell recognition of cancer cells, specifically as markers for NK sensitivity in carcinoma cell lines. The significance of T antigens as targets for NK cell-mediated lysis is novel and identifies NK cell-T antigen interactions as potentially significant in the immunotherapy of cancer and its associated metastases.