Failure of Neuraminidase to unmask Histocompatibility Antigens on Trophoblast

DURING outbred pregnancy the mother is exposed to genetically foreign tissue because the offspring inherits transplantation antigens from the father. The survival of the foetus is ensured by the intervention of the trophoblast which does not express transplantation antigens between mother and foetus: mouse trophoblast is not rejected even when transplanted into immune recipients^1,3. The mechanism of this failure to express histocompatibility antigens is not understood^1–4, but Kirby et al. have suggested that the extracellular fibrinoid surrounding trophoblast cells is involved^5,6. Currie has suggested that the thick sialomucinous glycocalyx of the trophoblast cell might “mask” the histocompatibility antigens on the trophoblast^7,8 and has demonstrated that neuraminidase unmasked these antigens⁸. Our experiments, however, show that trophoblast incubated with neuraminidase cannot sensitize allogeneic mice to donor histocompatibility antigens. Furthermore, pretreatment of trophoblastic implants with neuraminidase did not interfere with their proliferation and growth in highly immune allogeneic recipients.     

Binding of Radioactively Labelled Concanavalin A and Wheat Germ Agglutinin to Normal and Virus-transformed Cells

VARIOUS substances isolated from plants cause animal cells to clump. Several of these lectins¹ preferentially agglutinate cells which have been transformed spontaneously or by chemicals or viruses^2–7. The best known lectins of this class are concanavalin A (Con A) isolated from jack beans⁸ and wheat germ agglutinin⁴, which seem to bind to carbohydrate groups on the cell surface. The determinants recognized by the lectins seem to be N-acetyl-D-glucosamine for WGA⁴ and probably α-methyl-D-glucopyranoside for Con A⁶.     

Cell-free Studies on the Regulation of the Arabinose Operon

A DNA directed, cell-free system which synthesized L-ribulokinase coded by the L-arabinose operon ara OIBAD, has been developed. L-arabinose but not the araC gene product is required for the expression of this operon and, in addition, cyclic AMP and guanosine tetraphosphate are needed for optimal synthesis.     

Cooperation between Carrier-reactive and Hapten-sensitive Cells <Emphasis Type="Italic">in vitro</Emphasis>

THE mechanism, known as the carrier effect, whereby immunity to one or more determinant groups enhances the response to other determinants on the same multivalent antigen, was first recognized in delayed hypersensitivity to haptens, in which, for an appreciable response, the hapten must be coupled to the same protein carrier for priming and challenge^{1, 2}. Carrier specificity has also been demonstrated in the secondary antibody responses to hapten protein conjugates³. Two alternative hypotheses have been advanced to explain this specificity. The “local environment” hypothesis supposes that the hapten-sensitive cell recognizes both the hapten and the carrier determinants. However, the antihapten antibodies produced do not distinguish details of the carrier molecule and so do not reflect the specificity of the cellular receptor. Furthermore, inert spacer molecules inserted between hapten and carrier do not interfere with carrier specificity in the antibody response³. Reflecting current views on the cooperation between thymus-derived (T) and bone marrow derived (B) lymphocytes in the antibody response to various antigens⁴, the second hypothesis invokes two or more cells, one with receptors directed towards the hapten (hapten-sensitive cell), the others specific for the carrier molecule proper (carrier-reactive cells). Supporting this is the observation that pre-immunization to a particular protein carrier alone could potentiate the primary or secondary antihapten response to a hapten conjugated to that protein⁵. In an adoptive transfer system, moreover, the efficiency of antihapten antibody production by cells primed to a particular hapten-protein conjugate and stimulated with the hapten conjugated on a heterologous protein, is significantly enhanced by the introduction of cells primed to the heterologous carrier alone. Anti-carrier serum antibody does not cause such enhancement⁶. The carrier-reactive cells must therefore cooperate in increasing the efficiency of the hapten-sensitive cells in some way other than by providing humoral anti-carrier antibody. Recent work strongly suggests that carrier reactive cells are thymus-derived^{6, 7}.     

Function of the <Emphasis Type="Italic">rel</Emphasis> Gene in <Emphasis Type="Italic">Escherichia coli</Emphasis>

Sokawa et al. suggest that rel^- strains of Escherichia coli possess abnormal protein synthesizing machinery, which cannot carry out normal protein synthesis when the supply of amino-acids is limited.     

“Pleiotypic Response”

A hypothesis has been developed to relate stringent control in bacteria to a set of interactions involved in the regulation of growth of transformed and untransformed mammalian cells.     

Inhibition of DNA Synthesis but not of Poly-dAT Synthesis by the Arabinose Analogue of Cytidine <Emphasis Type="Italic">in vitro</Emphasis>

Kimball and Wilson¹ reported that the arabinose analogue of cytidine (ara-C) inhibited DNA polymerase in a crude extract prepared from Ehrlich ascites cells. Furth and Cohen² observed cytosine arabinoside triphosphate (ara-CTP) inhibited DNA polymerase in extracts from either calf thymus or bovine lymphosarcoma tissue, although these investigators³ had already found no effect of ara-CTP on DNA polymerase from Escherichia coli. The inhibition in both of these cases could be substantially reversed by dCTP; but incorporation of the arabinose nucleotide (ara-CMP) into DNA could not be unequivocally demonstrated. Graham and Whitmore⁴ reported the incorporation of ara-C into DNA in vivo and the inhibition of a DNA polymerase from L cells by ara-CTP. They found that ara-CMP was initially incorporated into small DNA strands but subsequently appeared in long strands. Momparler⁵ has presented evidence that, in vitro, ara-C incorporation was limited to the 3′-hydroxyl end of DNA chains. Such incorporation might be expected to block further chain elongation but this expectation was not supported by the evidence presented by Graham and Whitmore.     

Endopeptidase Activity of Phage λ-Endolysin

JACOB and Fuerst^1,2 demonstrated the presence of a bacteriolytic enzyme (λ-endolysin) in the induced cultures of lysogenic Escherichia coli K12 (λ). The enzyme was later identified as the product of gene R; of phage λ³ which is involved in bacterial lysis at the end of a latent period. The enzyme is apt to form spheroplast-like structures in E. coli² and one would therefore expect its substrate to be murein.