Isolation and characterization of two mouse L cell lines resistant to the toxic lectin ricin.

Two variant mouse L cell lines (termed CL 3 and CL 6) have been selected for resistant to ricin, a galactose-binding lectin with potent cytotoxic activity. The resistant lines exhibit a 50 to 70% decrease in ricin binding and a 300- to 500-fold increase in resistance to the toxic effects of ricin. Crude membrane preparations of CL 3 cells have increased sialic acid content (200% of control), while the galactose, mannose, and hexosamine content is within normal limits. Both the glycoproteins and glycolipids of CL 3 cells have increased sialic acid, with the GM3:lactosylceramide ratios for parent L and CL 3 cells being 0.29 and 1.5, respectively. In contrast, the membranes of CL 6 cells have a decrease in sialic acid, galactose, and hexosamine content with mannose being normal. Both cell lines have specific alterations in glycosyltransferase activities which can account for the observed membrane sugar changes. CL 3 cells have increased CMP-sialic acid:glycoprotein sialyltransferase and GM3 synthetase activities, while CL 6 cells have decrease UDP-GlcNAc:glycoproteinN-acetylglucosaminyltransferase and DPU-galactose:glycoprotein galactosyltransferase activities. The increased sialic acid content of CL 3 cells serves to mask ricin binding sites, since neuraminidase treatment of this cell line restores ricin binding to essentially normal levels. However, the fact that neuraminidase-treated CL 3 cells are still 45-fold resistant to ricin indicates that either a special class of productive ricin binding sites is not being exposed or that the cell line has a second mechanism for ricin resistance.     

Stimulation of receptor-mediated low density lipoprotein endocytosis in neuraminidase-treated cultured bovine aortic endothelial cells

Sialic acids, occupying a terminal position in cell surface glycoconjugates, are major contributors to the net negative charge of the vascular endothelial cell surface. As integral membrane glycoproteins, LDL receptors also bear terminal sialic acid residues. Pretreatment of near-confluent, cultured bovine aortic endothelial cells (BAEC) with neuraminidase (50 mU/ml, 30 min, 37 degrees C) stimulated a significant increase in receptor-mediated 125I-LDL internalization and degradation relative to PBS-treated control cells. Binding studies at 4 degrees C revealed an increased affinity of LDL receptor sites on neuraminidase-treated cells compared to control BAEC (6.9 vs. 16.2 nM/10(6) BAEC) without a change in receptor site number. This enhanced LDL endocytosis in neuraminidase-treated cells was dependent upon the enzymatic activity of the neuraminidase and the removal of sialic acid from the cell surface. Furthermore, enhanced endocytosis due to enzymatic alteration of the 125I-LDL molecules was excluded. In contrast to BAEC, neuraminidase pretreatment of LDL receptor-upregulated cultured normal human fibroblasts resulted in an inhibition of 125I-LDL binding, internalization, and degradation. Specifically, a significant inhibition in 125I-LDL internalization was observed at 1 hr after neuraminidase treatment, which was associated with a decrease in the number of cell surface LDL receptor sites. Like BAEC, neuraminidase pretreatment of human umbilical vein endothelial cells resulted in enhanced receptor-mediated 125I-LDL endocytosis. These results indicate that sialic acid associated with either adjacent endothelial cell surface molecules or the endothelial LDL receptor itself may modulate LDL receptor-mediated endocytosis and suggest that this regulatory mechanism may be of particular importance to endothelial cells.     

Effect of neuraminidase treatment of cells and effect of soluble glycoproteins on type 3 reovirus attachment to murine L cells.

The effect of pretreatment of murine L cells with bacterial neuraminidases on type 3 reovirus attachment was examined. We observed that such treatments resulted in a 60 to 80% decrease of subsequent attachment of 35S-labeled type 3 reovirus in a time- and dose-dependent manner. This result was specific for removal of cell surface sialic acid residues since the specific neuraminidase inhibitor 2-deoxy-2,3-dehydro-n-acetyl neuraminic acid completely prevented the observed effect. Although the total amount of radiolabeled virus bound to neuraminidase-treated cells was greatly reduced, unlabeled reovirus competed only slightly less efficiently for the attachment of 35S-labeled reovirus to neuraminidase-treated versus mock-treated L cells, suggesting that the specificity of the virus interaction with cellular receptor sites was only slightly diminished. Saturation experiments with mock-treated cells or with cells treated with Vibrio cholerae or with V. cholerae plus Arthrobacter ureafaciens neuraminidases indicated that the number of specific cellular receptor sites for type 3 reovirus were reduced by about 47%. We determined that under the neuraminidase digestion conditions used in this experiment we were able to remove a maximum 75% of the total N-acetylneuraminic acid of L cells. Our results also demonstrated that glycoproteins bearing a large amount of sialic acid containing oligosaccharides as well as purified N-acetylneuraminic acid, N-glycolylneuraminic acid, and N-acetylneuraminyl lactose were inhibitors of attachment, while proteins containing no sialic acid or negligible amounts of sialic acid did not inhibit attachment. High concentrations of various monosaccharides and lactose had no effect on reovirus attachment, in agreement with the recent results of Armstrong and his collaborators (Armstrong et al., Virology, 138:37-48, 1984). These data are also supported by the observation that gangliosides are inhibitors of viral attachment (Armstrong et al., Virology, 138:37-48, 1984). Taken together, our results suggest that cell surface sialic acid-containing glycoconjugates are involved in type 3 reovirus binding to murine L cells.     

Disposition of glycoproteins in plasma membrane of cultured rat embryonic fibroblasts

Plasma membrane fractions were isolated from untreated and trypsin- or neuraminidase-treated rat embryo fibroblasts and their sialic acids contents per mg membrane protein were determined. The difference represented enzyme releasable sialic acid exposed on the medium side of the cell mambrane. It was 14 to 23% of the total membrane bound sialic acid. Isolated plasma membrane fraction from entreated and enzyme treated cells were then subjected to trypsin or neuraminidase treatment to obtain enzyme-releasable sialic acid from both faces and from the cytoplasmic face of the membrane respectively. Between 30 and 50% of the total membrane bound sialic was released from both the faces and 14 to 30% from the cytoplasmic face. An average of 59% was insusceptible to these enzymes. As an alternative to a cytoplasmic location of sialic acid containing membrane constituents, inaccessibility of enzymes to some of these constituents present on the surface of intact cells is considered.Sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis of plasma membrane fractions isolated from untreated and trypsin treated cells and of trysinized plasma membrane fraction was carried out to know the number and gel migration of proteins and glycoproteins which are exposed on each of the two faces of the plasma membrane and are sensitive or insensitive to trypsin. The resilts obtained were confirmed by SDS-polyacrylamide gel electrophoresis of untreated and trypsin-treated cells and of isolated plasma membrane fraction after subjecting them to enzymatic radioiodination.     

Fusion properties of cells persistently infected with human parainfluenza virus type 3: participation of hemagglutinin-neuraminidase in membrane fusion.

Cells persistently infected with human parainfluenza virus type 3 (HPF3) exhibit a novel phenotype. They are completely resistant to fusion with each other but readily fuse with uninfected cells. We demonstrate that the inability of these cells to fuse with each other is due to a lack of cell surface neuraminic acid. Neuraminic acid is the receptor for the HPF3 hemagglutinin-neuraminidase (HN) glycoprotein, the molecule responsible for binding of the virus to cell surfaces. Uninfected CV-1 cells were treated with neuraminidase and then tested for their ability to fuse with the persistently infected (pi) cells. Neuraminidase treatment totally abolished cell fusion. To extend this result, we used a cell line deficient in sialic acid and demonstrated that these cells, like the neuraminidase-treated CV-1 cells, were unable to fuse with pi cells. We then tested whether mimicking the agglutinating function of the HN molecule with lectins would result in cell fusion. We added a panel of five lectins to the neuraminic acid-deficient cells and showed that binding of these cells to the pi cells did not result in fusion; the lectins could not substitute for interaction of neuraminic acid with the HN molecule in promoting membrane fusion. These results provide compelling evidence that the HN molecule of HPF3 and its interaction with neuraminic acid participate in membrane fusion and that cell fusion is mediated by an interaction more complex than mere juxtaposition of the cell membranes.     

The role of cell surface sialic acid in insulin receptor function and insulin action

Removal of cell surface sialic acid from adipocytes with neuraminidase inhibits insulin action. Here, we have examined the effects of mild neuraminidase treatment (5 milliunits/ml, 12 degrees C, 15 min) on insulin receptor structure and function. Neuraminidase treatment sufficient to cause greater than 90% loss of insulin stimulatable lipogenesis had no effect on 125I-insulin binding, tyrosine kinase activity of partially purified insulin receptors, insulin receptor phosphorylation in intact cells, or insulin-induced receptor internalization. However, recycling of the insulin receptor to the plasma membrane was inhibited by 50%. Recycled receptors in neuraminidase-treated cells were unable to mediate insulin action in contrast to recycled receptors from non-neuraminidase-treated cells. Furthermore, when insulin receptors were protected from exposure to neuraminidase, by inducing receptor internalization prior to neuraminidase treatment, the cells were still unable to respond to insulin. Analysis of the alpha and beta subunits of the receptor from neuraminidase-treated cells, affinity-labeled with 125I-insulin, or labeled by autophosphorylation, and subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis failed to indicate any changes in the holoreceptor or the individual subunits. This suggests there was no detectable release of sialic acid from the receptor. From this data we conclude that loss of sialic acid from nonreceptor glycoconjugates leads to loss of insulin action and inhibition of receptor recycling. The insulin receptor does not appear to be involved in this inhibitory effect. These findings suggest that an uncharacterized plasma membrane glycoprotein is essential in transmitting the "signal" of insulin binding to the cellular effector system.     

The effect of neuraminidase on the relative surface charge-associated properties of rat red blood cells of different ages

Approx. 70% of the sialic acid on the rat erythrocyte surface is susceptible to cleavage by neuraminidase (Vibrio cholerae). Neuraminidase treatment results in a reduction in the partition coefficient (K) of the red cells in a charged dextran-poly(ethylene glycol) aqueous phase system and in the electrophoretic mobility of the cells. Countercurrent distribution of rat neuraminidase-treated erythrocytes, containing 59Fe-labeled mature red cells of distinct age, indicates that (a) the electrophoretic mobilities of red cells in different cavities along the extraction train increase with increasing K, as is the case with untreated erythrocytes, and (b) the cell age-related differences in surface charge-associated properties are neither eliminated nor altered by the enzyme action.     

A new assay for cell-bound neuraminidase

Summary A new way of detecting neuraminidase activity on the surface of neuraminidase-treated cells is described. It consists of an enzymatic assay with radiolabelled cells as substrate. It shows that the enzyme borne by one cell is able to cleave sialic acid to another cell.     

Cell surface sialylation and tumor metastasis. Metastatic potential of B16 melanoma variants correlates with their relative numbers of specific penultimate oligosaccharide structures

Numerous investigations suggest that cell surface glycoconjugates, and in particular sialic acids, are directly involved in determining the metastatic phenotype. To further evaluate this hypothesis, we have used a variety of techniques to probe the cell surfaces of several metastatic variants of the murine B16 melanoma that were selected for experimental lung-colonizing ability (Fidler, I. (1973) Nature 242, 148-149) or for their ability to spontaneously metastasize from the site of a subcutaneous injection (Stackpole, C. W., Alterman, A. L., and Fornabaio, D. M. (1985) Invasion & Metastasis 5, 125-142). Using a highly sensitive high performance liquid chromatography sialic acid assay in conjunction with Vibrio cholerae sialidase, we find that none of these metastatic variants differ significantly in their overall levels of cell surface sialic acid. Using highly purified, linkage-specific sialyltransferases, in conjunction with specific glycosidases, to probe the cell surface saccharide topography of specific penultimate oligosaccharides, we also find no significant differences between the efficient lung-colonizing variant, B16-F10 and the poorly-colonizing B16-F1 or B16-Flr variants. In contrast, the spontaneously metastatic variants examined contain substantially different levels of specific penultimate sialylation sites. The tumorigenic but nonmetastatic B16-LM3/G3.26 variant contains 4-fold more penultimate Gal beta 1-3GalNAc sialylation sites than the tumorigenic and highly metastatic B16-LM3/G3.12 variant when CMP[3H]NeuAc and the alpha 2-3Gal beta 1-3GalNAc sialyltransferase are used to probe the melanoma cell surfaces. Several prominent glycoconjugates of apparent Mr 43,000, 40,000, and 30,000 are especially evident upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the nonmetastatic cells. The nonmetastatic variant also contains 2-fold more Gal beta 1-4GlcNAc sialylation sites than the metastatic variant when the alpha 2-6Gal beta 1-4GlcNAc sialyltransferase is used as a cell surface probe. In this case, glycoconjugates of apparent Mr 74,000, 45,000, and 43,000 are more prominently observed on the cell surfaces of the nonmetastatic variant. These data indicate that the differences in lung-colonizing abilities of B16 melanoma metastatic variants do not correlate with the numbers or sialylation states of specific penultimate oligosaccharide structures on their surfaces. However, the relative levels of specific penultimate saccharide structures do correlate with the ability of the cells to undergo spontaneous metastasis from a subcutaneous tumor.     

Immobilized alpha2,6-linked sialic acid suppresses caspase-3 activation during anti-IgM antibody-induced apoptosis in Ramos cells

In Ramos cells, a human Burkitt's lymphoma cell line, stimulation of the B cell antigen receptor with anti-IgM antibody (Ab) induces apoptosis as indicated by a decrease in cell viability and an increase in DNA fragmentation and cell surface exposure of phosphatidylserine. Furthermore, these changes are suppressed by incubating the cells in alpha(1)-acid glycoprotein (AGP)-coated tissue culture plates. Here, we found that, during Anti-IgM Ab-induced apoptosis in Ramos cells, caspase-3 is activated downstream of caspase-8 and the mitochondrial pathway is activated, as indicated by a loss of mitochondrial membrane potential, an increase in the release of cytochrome c to the cytoplasm, and enhanced Bax expression. Anti-IgM Ab-induced apoptosis of neuraminidase-treated Ramos cells was suppressed by incubating the cells on plates coated with AGP, which contains a high concentration of alpha2,6-linked sialic acid. The incubation on plates coated with AGP also suppressed anti-IgM Ab-stimulated caspase-3 activity and increased the level of X-linked inhibitor of apoptosis protein (XIAP), but it did not affect caspase-8 activity, the mitochondrial membrane potential, cytochrome c release, or Bax expression. The results indicate that the interaction of Ramos cells with immobilized alpha2,6-linked sialic acid enhances XIAP expression, directly or indirectly suppressing caspase-3 activity and inhibiting anti-IgM Ab-induced apoptosis.     

The VP5 domain of VP4 can mediate attachment of rotaviruses to cells

Some animal rotaviruses require the presence of sialic acid (SA) on the cell surface to infect the cell. We have isolated variants of rhesus rotavirus (RRV) whose infectivity no longer depends on SA. Both the SA-dependent and -independent interactions of these viruses with the cell are mediated by the virus spike protein VP4, which is cleaved by trypsin into two domains, VP5 and VP8. In this work we have compared the binding characteristics of wild-type RRV and its variant nar3 to MA104 cells. In a direct nonradioactive binding assay, both viruses bound to the cells in a saturable and specific manner. When neutralizing monoclonal antibodies directed to both the VP8 and VP5 domains of VP4 were used to block virus binding, antibodies to VP8 blocked the cell attachment of wild-type RRV but not that of the variant nar3. Conversely, an antibody to VP5 inhibited the binding of nar3 but not that of RRV. These results suggest that while RRV binds to the cell through VP8, the variant does so through the VP5 domain of VP4. This observation was further sustained by the fact that recombinant VP8 and VP5 proteins, produced in bacteria as fusion products with glutathione S-transferase, were found to bind to MA104 cells in a specific and saturable manner and, when preincubated with the cell, were capable of inhibiting the binding of wild-type and variant viruses, respectively. In addition, the VP5 and VP8 recombinant proteins inhibited the infectivity of nar3 and RRV, respectively, confirming the results obtained in the binding assays. Interestingly, when the infectivity assay was performed on neuraminidase-treated cells, the VP5 fusion protein was also found to inhibit the infectivity of RRV, suggesting that RRV could bind to the cell through two sequential steps mediated by the interaction of VP8 and VP5 with SA-containing and SA-independent cell surface receptors, respectively.     

Physiological ageing of red blood cells and changes in membrane carbohydrates

Evidence is presented to indicate a generalized role for the terminal sialic acid residues of circulating erythrocytes. After reinjection into their donors, neuraminidase-treated human, rabbit, rat and dog erythrocytes were promptly removed from the circulation : intect erythrocytes, previously incubated under the same conditions but without neuraminidase, were removed after a significantly longer period. The neuraminidase-treated erythrocytes were cleared by the liver and in a little part by the spleen. Old and young human, rabbit, rat erythrocytes contained different quantities of stromal sialic acid, significantly lowered on the old cells. But the half-life of old intact rabbit erythrocytes is sigificantly shorter than that of neuraminidase-treated young erythrocytes with a similar minidase-treated young erythrocytes with a similar sialic acid content. Indeed sialic acid is not the only carbohydrate component of the membrane that is decreased during erythrocyte ageing, the others membranous sugars are decreased too. Theses changes in the carbohydrate moity could have a role in the clearance of the erythrocytes.     

Membranes of animal cells. VIII. Distribution of sialic acid,hexosamines and sialidase in the L cell

The distribution of sialic acid and hexosamines was studied in purified organelles obtained from L cells. The major portion of the sialic acid of the intact cell is found in the surface membranes (66%). Only small amounts of sialic acid are found in the other purified fractions with the exception of the lysosomes which contained approx. 16%. The hexosamines are largely distributed between the surface membranes (33%) and soluble fraction (25%). Microsomes and mitochondria contain 14 and 11%, respectively, of the hexosamines of the intact cell and the nuclei contain 4%. The molar ratio of hexosamines to sialic acid of these fractions indicate differences in glycoprotein and/or glycolipid contents of the cell organelles.     

Total sialic acid content of glycophorins during senescence of human red blood cells.

Glycophorins extracted from membranes of young and old human red blood cells have within an error of +/- 1.5% the same sialic acid content when referred to a relative measure of the number of glycophorins. The degree of surface iodination in glycophorins, which was shown to be the same in young and old cells, served as this relative measure. This finding implies that senescent human red blood cells hardly reveal desialylated surface proteins (less than or equal to 3%). However, the sialic acid content per cell was repeatedly reported to be 10 to 15% lower in old than in young cells. Therefore, we conclude 1) that human red blood cells lose intact glycophorin together with membrane during red blood cell senescence, and 2) that removal of desialylated and senescent red blood cells from the circulation proceeds by different routes.     

The electrophoretic mobility of normal and leukaemic cells of mice

1. The pH-mobility relationships for saline-washed cells from a mouse strain of acute lymphoblastic leukaemia were examined before and after treatment with lower aldehydes, diazomethane and neuraminidase (EC 3.2.1.18). 2. The content of sialic acid released into the supernatant fluid of neuraminidase-treated cells was measured. 3. The stability of the charge-determining structures to temporary changes in environment (pH and ionic strength) was established. 4. Similar measurements were made on lymph-node cells obtained from non-leukaemic mice (a resistant and a leukaemia-susceptible strain were examined). 5. It is deduced that both the malignant and the non-malignant cell possess two dissociable acid functions at the cell surface, a carboxyl group of sialic acid and another acidic group(s), probably carboxyl, of pK 3.0-4.5. The malignant cells, however, have a basic dissociable function not present in the non-malignant types. 6. Suggestions are made as to how the difference in surface chemistry may be related to the problem of malignancy.     

Conformational alterations within the glycocalyx of erythrocyte membranes studied by spin labelling

The structure of the glycocalyx of the membrane of human erythrocytes and spectrin-depleted vesicles was studied under various conditions by two spin-labelling approaches: covalently labelling sialic acid residues of the glycocalyx and incorporation of a charged hydrophobic spin probe, CAT 16, being sensitive to alterations on the membrane surface into the lipid phase. Although cell electrophoretic measurements which were performed, additionally, indicated an erection of the glycocalyx upon decreasing the ionic strength of the suspension medium a more restricted mobility of spin-labelled sialic acid residues was found, in this case probably due to electrostatic interactions. The enhanced mobility of the spin probe CAT 16 at low ionic strength as well as in the case of neuraminidase-treated cells could be caused by reduced steric and electrostatic interaction with glycoproteins and glycolipids. La3+ adsorption and virus attachment on the human erythrocyte membrane were accompanied with a reduced mobility of sugar headgroups of the surface coat. No indication of cluster formation or lateral segregation of glycophorin molecules was found upon virus binding. After denaturation of the spectrin cytoskeleton of intact erythrocytes, increased mobility of spin-labelled sialic acid residues was observed.     

Cellular adsorption function of the sialoglycoprotein of vesicular stomatitis virus and its neuraminic acid.

Exposure of vesicular stomatitis (VS) virions to neuraminidase resulted in loss of their ability to agglutinate goose erythrocytes and to attach to L cells concomitant with hydrolysis of sialic acid. These viral adsorptive functions were also destroyed by tryspsinization. Sialyl transferase resialylation in vitro of neuraminidase-treated VS virions restored their hamagglutinating and adsorptive functions almost to original levels. Erythrocyte and L cell receptors for attachment of VS virions were blocked by fully sialylated fetuin and by VS viral sialoglycopeptides. Smaller VS viral glycopeptides generated by extensive trypsinization were less effective inhibitors of hemagglutination than were larger glycopeptides; neuraminic acid and neuraminosyl lactose had no capacity to inhibit hamagglutination or adsorption of virus to L cells. These data suggest that cellular receptors for viral adsorption recognize sialoglycopeptides of a certain size. Neuraminidase desialylation did not significantly alter the isoelectric point of VS virions. Cells exposed to DEAE-dextran, trypsin, or neuraminidase showed significantly increased capacity to attach fully sialylated but not desialylated VS virions. Neuraminidase desialylation of L cells, Chinese hamster ovary cells, and Madin-Darby bovine kidney cells resulted in enhanced susceptibility to plaque formation by VS virus.     

Immobilized α2,6-linked sialic acid suppresses caspase-3 activation during anti-IgM antibody-induced apoptosis in Ramos cells

In Ramos cells, a human Burkitt's lymphoma cell line, stimulation of the B cell antigen receptor with anti-IgM antibody (Ab) induces apoptosis as indicated by a decrease in cell viability and an increase in DNA fragmentation and cell surface exposure of phosphatidylserine. Furthermore, these changes are suppressed by incubating the cells in α₁-acid glycoprotein (AGP)-coated tissue culture plates. Here, we found that, during Anti-IgM Ab-induced apoptosis in Ramos cells, caspase-3 is activated downstream of caspase-8 and the mitochondrial pathway is activated, as indicated by a loss of mitochondrial membrane potential, an increase in the release of cytochrome c to the cytoplasm, and enhanced Bax expression. Anti-IgM Ab-induced apoptosis of neuraminidase-treated Ramos cells was suppressed by incubating the cells on plates coated with AGP, which contains a high concentration of α2,6-linked sialic acid. The incubation on plates coated with AGP also suppressed anti-IgM Ab-stimulated caspase-3 activity and increased the level of X-linked inhibitor of apoptosis protein (XIAP), but it did not affect caspase-8 activity, the mitochondrial membrane potential, cytochrome c release, or Bax expression. The results indicate that the interaction of Ramos cells with immobilized α2,6-linked sialic acid enhances XIAP expression, directly or indirectly suppressing caspase-3 activity and inhibiting anti-IgM Ab-induced apoptosis.     

Initiation of apoptosis and autophagy by photodynamic therapy

This study was designed to examine modes of cell death after photodynamic therapy (PDT). Murine leukemia L1210 cells and human prostate Bax-deficient DU-145 cells were examined after PDT-induced photodamage to the endoplasmic reticulum (ER). Previous studies indicated that this treatment resulted in a substantial loss of Bcl-2 function. Both apoptosis and autophagy occurred in L1210 cells after ER photodamage with the latter predominating after 24 hr. These processes were characterized by altered cellular morphology, chromatin condensation, loss of mitochondrial membrane potential and formation of vacuoles containing cytosolic components. Western blots demonstrated processing of LC3-I to LC3-II, a marker for autophagy. In DU145 cells, PDT initiated only autophagy. Phosphatidylinositol (PI) 3-kinase inhibitors suppressed autophagy in both cell lines as indicated by inhibition of vacuolization and LC3 processing. Inhibitors of apoptosis and/or autophagy were then used to delineate the contributions of the two pathways to the effects of PDT. Given the ability of autophagy to upregulate MHC-11 peptide presentation, autophagy may play a role in the ability of photodynamic therapy to stimulate immunologic recognition of target cells.     

Novel glycosylation-defective baby hamster kidney cells.

The plant lectin wheat germ agglutinin (WGA) has previously been used to select more than ten different glycosylation-defective phenotypes in a variety of mammalian somatic cells. Three WGA-resistant phenotypes have now been obtained spontaneously from baby hamster kidney (BHK) cells. These mutant BHK cells exhibit a pattern of cross resistance and sensitivity to multiple plant lectins, suggesting that the cell surface carbohydrates of these cells are altered. Two WGA-resistant BHK phenotypes appear similar to WGA-resistant CHO cells that lack terminal sialic acid and galactose residues on their cell surface carbohydrates. The third WGA-resistant BHK cell phenotype has not previously been seen in WGA-resistant mammalian cells.