Ricin, a galactose-binding lectin with potent cytotoxic activity, was used to select a clone of Chinese hamster ovary cells with altered plant lectin-binding properties. The clone (15B) is 80-fold less sensitive to the toxic action of ricin than the parent line. In the absence of ricin, it grows both in monolayer and suspension culture with a normal generation time. Plating efficiency, however, is significantly reduced. Relative to the parent cells, its binding of the Ricinus communis lectins, Phaseolus vulgaris erythroagglutinating phytohemagglutinin, Abrus precatorius phytohemagglutinin, and soybean phytohemagglutinin is less than 7%, while binding of lentil phytohemagglutinin, wheat-germ agglutinin, and mushroom phytohemagglutinin is 17%, 40%, and 109%, respectively. In contrast, its concanavalin A binding is increased by 70%.Consistent with these alterations, crude membrane preparations of the 15B cells were found to contain the same sugars as the parent-cell membranes but in different proportions. The 15B membranes have 28% less sialic acid, 38% less N-acetylglucosamine, 49% less galactose, the same amount of N-acetylgalactosamine, and 53% more mannose than the membranes of the parent cells.

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Sindbis and vesicular stomatitis viruses were grown in a line (termed 15B) of Chinese hamster ovary (CHO) cells that is deficient in a specific UDP-N-acetylglucosamine:glycoprotein N-acetylglucosaminyltransferase. Both viruses replicated normally in the cell line, but the glycoproteins of the released virus migrated faster on sodium dodecyl sulfate-polyacrylamide gels than did glycoproteins of virus grown in parent CHO cells. Digestion of the viral glycoproteins with Pronase followed by gel filtration demonstrated that the glycopeptides of Sindbis-15B virus were much smaller than the glycopeptides of Sindbis-CHO virus. In addition, Sindbis-15B viral glycopeptides but not Sindbis-CHO viral glycopeptides contained terminal a-mannose residues as shown by their susceptibility to a-mannosidase digestion. These findings demonstrate that the oligosaccharide units of the glycoproteins of vesicular stomatitis and Sindbis viruses are altered when the viruses are grown in 15B cells. We conclude that the N-acetylglucosaminyltransferase that is missing in 15B cells normally participates in the biosynthesis of the oligosaccharide units of the viral glycoproteins, and in the absence of this enzyme incomplete oligosaccharide chains are produced. Viruses released from 15B cells appear to retain full infectivity; Sindbis-15B virus, however, showed a significant decrease in hemagglutination titer compared with that of Sindbis-CHO virus. Enveloped RNA viruses, such as Sindbis and vesicular stomatitis virus (VSV), contain glyco

Complement (C) activity present in normal human serum has been reported to lyse circulating forms of Trypanosoma cruzi following activation by specific host antibodies bound to the surface of the parasites. In view of this observation, we examined the possibility that a similar phenomenon may cause lysis of T. cruzi by avian complement, a mechanism postulated to be responsible for the natural resistance of birds to T. cruzi infection and previously described as being antibody independent. Trypomastigote forms of T. cruzi grown either in lethally irradiated mice or in cell cultures were lysed readily by the sera of agammaglobulinemic chickens. Lytic activity and titers of normal and agammaglobulinemic sera were comparable. The lytic reaction was inhibited by heat inactivation of the sera, or by addition of EDTA or cobra venom factor to the assay mixtures. Lysis of T. cruzi was observed when calcium, but no magnesium ions, were chelated with EGTA. Furthermore, a significant loss of lytic activity was observed when sera from C-depleted chickens were tested. Normal and agammaglobulinemic chickens cleared intravenously injected parasites (from either lethally irradiated mice or cell cultures) from their circulation in 7 min or less whereas C-depleted animals required 1,740 min or longer. Routine examination of the parasites from these two sources by immunofluorescence confirmed the absence of immunoglobulins on their surface. These results emphasize the lack of requirement of antibodies for, and the important role of complement in both the natural resistance that birds exhibit against T. cruzi infection and the lytic activity displayed by avain serum on virulent forms of T. cruzi.

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Two mouse L cell variant lines (CL 3 and CL 6) selected for resistance to the toxic plant lectin ricin were restricted in their ability to replicate the two alphaviruses Sindbis virus and Semliki Forest virus. CL 3 cells have been shown to exhibit increased CMP-sialic acid:glycoprotein sialyltransferase and GM3 synthetase activities, whereas CL 6 cells have been shown to contain decreased UDPgalactose:glycoprotein galactosyltransferase and UDP-N-acetylglucosamine:glycoprotein N-acetylglucosaminyltransferase activities. The adsorption of Sindbis virus to CL 6 cells was considerably reduced, suggesting that the loss or inaccessibility of the receptors for Sindbis virus accounted for a major defect in virus production in these cells. In contrast, CL 3 synthesized Sindbis viral RNA and proteins but were unable to convert the precursor glycoprotein PE2 to the structural protein E2. The cleavage of PE2 to E2 was also blocked in both CL 3 and CL 6 cells infected with Semliki Forest virus.

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