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M Virji

Publications and source records attributed to M Virji.

At least 73 records · Page 4Linked to original sources
PubMed1988

Nonbactericidal antibodies against Neisseria gonorrhoeae: evaluation of their blocking effect on bactericidal antibodies directed against outer membrane antigens.

Nonbactericidal monoclonal antibodies (MAbs) directed against gonococcal surface antigens were examined for their effect on complement-mediated bactericidal killing by other MAbs and normal human serum. One MAb, SM73, directed against the H.8 antigen activated complement only moderately well and had little influence on bactericidal antibodies. Two antibodies directed against an epitope on protein III had very different effects. Antibody SM51 activated complement poorly and had no effect on bactericidal killing, whereas antibody SM50, although itself nonbactericidal, activated complement and blocked the bactericidal effect of other antibodies. The extent of the blocking ability of MAb SM50 was studied using MAbs of different specificities as well as polyclonal antisera raised against gonococcal surface antigens. Antibody SM50 blocked IgG MAbs of all specificities, but several MAbs of the IgM class retained their bactericidal effect. Each of these IgM MAbs reacted with lipopolysaccharide, but with different epitopes.

Antibodies, Bacterial↗
PubMed1987

Immunobiology of gonococcal outer membrane protein I.

Monoclonal antibodies have been obtained which react with gonococcal outer membrane protein I. One antibody recognised the majority of strains expressing P.IA and another recognised the majority of strains expressing P.IB. In in vitro tests both antibodies were bactericidal in the presence of complement, opsonic for phagocytosis by human PMN and protected epithelial cells against gonococcal invasion. Thus conserved epitopes on P.I. are potentially effective targets for immunoprophylaxis.

Animals↗
PubMed1987

Outer membrane protein III of Neisseria gonorrhoeae: variations in biological properties of antibodies directed against different epitopes.

Monoclonal antibodies (mAbs) have been raised to gonococcal outer membranes. A panel of six mAbs was identified by several criteria as reacting with outer membrane protein III (P.III). Competitive radioimmunoassays showed that the mAbs could be grouped into three pairs recognizing different epitopes on P.III. These epitopes are equally present on all pathogenic Neisseria. The mAbs demonstrated differing protective effects in model systems. Those directed against one epitope were particularly effective in protecting Chang conjunctiva epithelial cells against gonococcal challenge. mAbs against this epitope and another promoted complement-mediated bactericidal activity, while those directed against the third epitope were ineffective. Thus the biological effects of mAbs directed against P.III vary according to the epitope recognized.

Antibodies, Monoclonal↗
PubMed1987

Localization of antibody-binding sites by sequence analysis of cloned pilin genes from Neisseria gonorrhoeae.

Immunological analysis of gonococcal pilin (the protein structural subunit of pili) has demonstrated the existence of cross-reacting and type-specific epitopes. The role in adhesion of the domains represented by these epitopes remains unclear. DNA sequencing of a series of pilin-expressing (pilE) genes from a number of otherwise isogenic pilus antigenic variants combined with previous immunological analysis of the corresponding encoded pilins has allowed us to correlate certain predicted amino acid sequences with monoclonal antibody reactivities. The putative epitopes for type-specific antibodies lie predominantly in hydrophilic domains that also contain beta turns. The epitopes for type-specific monoclonal antibodies were shown to depend on amino acid changes either in three separated blocks of amino acid sequence in the semi-variable (SV) region of pilin, or in discrete regions that lie in the disulphide loop in the hypervariable (HV) region of the polypeptide. In contrast, antibody SM1, which reacts with all gonococcal pili, recognizes a poorly immunogenic region of moderate hydrophilicity but low turn potential lying in a conserved portion of the pilin molecule. Our results confirm that antibodies directed against epitopes in both the SV and HV regions are able to inhibit adhesion.

Amino Acid Sequence↗
PubMed1987

The potential protective effect of monoclonal antibodies to gonococcal outer membrane protein IA.

Hybrid cell lines were derived which produced monoclonal antibodies directed against gonococcal outer membrane protein IA. One antibody, SM101, recognized 24 P.IA-expressing strains out of 25 tested--the rest exhibited relatively less cross-reactivity. Competitive radioimmunoassays revealed that each antibody could effectively inhibit binding of the others, suggesting close proximity of the epitopes recognized. The antibodies were used in assays in vitro to investigate their potential efficacy in protection against gonococcal infection. In a cytotoxicity assay, the antibodies afforded some protection to epithelial cells challenged with gonococci. They were very effective at bactericidal killing in the presence of complement and, in addition, were opsonic for homologous and heterologous strains. The cross-reacting antibody, SM101, was one of the most effective in both assays. The results show that the conserved epitope on P.IA recognized by antibody SM101 is potentially an effective target on the gonococcal surface for immunoprophylaxis.

Antibodies, Monoclonal↗
PubMed1986

Effect of insulin on low-density-lipoprotein metabolism in human lymphocytes in vitro.

The metabolism of low-density lipoproteins (LDL) in vitro in the presence of insulin was studied in freshly isolated human peripheral-blood lymphocytes. Insulin appeared to decrease the binding affinity of 125I-LDL to its cell-surface receptor, without any change in apparent Vmax or in the number of LDL receptors. As a consequence, the absolute amounts of 125I-LDL internalized and degraded were lower in the presence of insulin than in its abscence, although the fraction of internalized 125I-LDL degraded in either instance was quite similar. 3-Hydroxy-3-methylglutaryl-CoA reductase activity, and hence cholesterol synthesis, were stimulated by insulin. This effect of insulin was independent of the inhibitory effect of LDL on cholesterol synthesis. At the same time, acid cholesterol esterase and acyl-CoA: cholesterol O-acetyltransferase activities were lower in cells incubated with insulin than in controls. The net effect of these metabolic alterations seems to be that cells accumulate greater quantities of free and esterified cholesterol when treated with insulin.

AMP-Activated Protein Kinases↗
PubMed1986

The effect of protein II and pili on the interaction of Neisseria gonorrhoeae with human polymorphonuclear leucocytes.

Colonial variants of Neisseria gonorrhoeae strain P9 expressing different pili and/or outer membrane protein II (P.II) were investigated with respect to their interaction with human polymorphonuclear leucocytes (PMN). Two assay systems were used. A phagocytic killing assay measured the intracellular survival of gonococci, and PMN chemiluminescence (CL) was used to determine the initial surface interactions. All variants expressing P.II were killed effectively by PMN and also greatly stimulated PMN CL. The P.II- variants, on the other hand, were resistant to phagocytic killing and stimulated a much lower CL response. The presence of different P.II species was associated with different CL profiles and therefore different modes of interaction with the PMN membrane. A P.II-specific monoclonal IgG was opsonic and greatly increased PMN CL in contrast to F(ab')2 prepared from the same antibody, which inhibited it, thus confirming the role of P.II in the PMN interaction. Phagocytic killing assays revealed that with the loss of P.II, gonococcal variants acquired resistance to killing. Comparison of piliated and non-piliated pairs of variants with the same P.II profile showed that PMN-gonococcal interactions are dominated by the nature of the P.II species present whereas pili have little effect.

Bacterial Outer Membrane Proteins↗
PubMed1986

Monoclonal antibodies to gonococcal outer membrane protein I: location of a conserved epitope on protein IB.

Hybrid cell lines have been derived which produce monoclonal antibodies reacting with outer membrane protein I from Neisseria gonorrhoeae strain P9. The antibodies obtained showed variable reactivity with other strains but one antibody recognized an epitope present on all of the strains tested which expressed the protease sensitive protein IB. Purified IgG labelled with 125I was used in competitive radioimmunoassays with unlabelled antibody to investigate the spacial distribution of the epitopes recognized. Each pair of antibodies showed some degree of inhibition. The relative magnitude of inhibition suggested that the conserved epitope lies within a variable region containing other epitopes which determine the antigenic specificity of the protein. Western blotting of peptides derived by proteolytic digestion of protein IB revealed that the conserved epitope is located close to the chymotrypsin cleavage site within a 7000 Mr surface exposed region of the molecule.

Antibodies, Bacterial↗
PubMed1986

Monoclonal antibodies to gonococcal outer membrane protein IB: use in investigation of the potential protective effect of antibodies directed against conserved and type-specific epitopes.

Several monoclonal antibodies directed against gonococcal outer membrane protein IB have been used in in vitro assays to investigate their potential efficacy in protection against gonococcal infection. In a cytotoxicity assay, virulence of the variant P9-17 for epithelial cells in tissue culture was reduced in the presence of three of the four antibodies which recognized type-specific epitopes. Similarly, virulence of P9-17 as well as a recent isolate was reduced in the presence of the one antibody, SM24, which reacted with a conserved epitope. This antibody was also bactericidal in the presence of complement, and in addition was opsonic for several protein IB-expressing strains as determined by polymorphonuclear leucocyte chemiluminescence measurements. Similarly, all the type-specific antibodies were opsonic for P9 variants. However, only two of these antibodies mediated complement-dependent killing although those which were ineffective were nevertheless complement-fixing antibodies. These results indicate that antibodies to closely positioned epitopes on protein I vary in their biological activities and that the conserved epitope recognized by the antibody SM24 is potentially an effective target on the gonococcal surface for immunoprophylaxis.

Antibodies, Bacterial↗
PubMed1985

Role of anti-pilus antibodies in host defense against gonococcal infection studied with monoclonal anti-pilus antibodies.

Several monoclonal antibodies directed against gonococcal pili have been used to investigate the potential contribution of anti-pilus antibodies to host defense against gonococcal infection. Included were two antibodies (SM1 and SM2) which reacted with conserved determinants present on pili from all strains tested and others which exhibited antigenic specificity. Immunoblotting experiments revealed that antibodies SM1 and SM2 recognize epitopes on two different peptides derived by CNBr cleavage of alpha-pili from Neisseria gonorrhoeae P9-2. All antibodies used were capable of activating complement, as shown by their ability to bind Clq, and one type-specific antibody was effective in complement-mediated bactericidal killing. Antibodies directed against at least some pilus epitopes may therefore contribute to bactericidal activity during the course of natural infection. The opsonic effect of type-specific antibodies was demonstrated by their ability to stimulate luminol-dependent chemiluminescence of human polymorphonuclear leukocytes and promote phagocytic killing of variant P9-2. Phagocytic killing in the presence of each monoclonal antibody paralleled the increase in chemiluminescence, suggesting that for this variant killing was an inevitable consequence of the interaction of polymorphonuclear leukocytes with gonococci opsonized with anti-pilus antibodies. Antibody-mediated chemiluminescence of polymorphonuclear leukocytes was enhanced in the presence of human complement, and a weak opsonic effect was detected with one of the cross-reacting antibodies (SM1) when this system was used. Although cross-reacting antibody SM1 and type-specific antibody SM13 showed considerable differences in biological properties, they were of the same isotype and bound to native pili on intact gonococci in similar numbers and with similar avidity.

Animals↗
PubMed1984

The role of common and type-specific pilus antigenic domains in adhesion and virulence of gonococci for human epithelial cells.

A panel of monoclonal antibodies with varying pilus specificities ranging from cross-reacting to type-specific has been used to investigate the role of conserved and variable antigenic domains in the adhesion of gonococci to human epithelial cells. The binding of 125I-labelled alpha pili from strain P9 to buccal epithelial cells was inhibited by three type-specific but not by two cross-reacting antibodies. Four type-specific antibodies inhibited the binding of gamma pili while the two cross-reacting antibodies were again without effect. The virulence of the variants P9-2 (alpha pili) and P9-35 (gamma pili) for Chang conjunctiva epithelial cells was similarly reduced only in the presence of relevant type-specific antibodies. These results indicate the importance of variable antigenic domains in the adhesion of gonococci to human epithelial cells.

Adhesiveness↗
PubMed1983

Monoclonal antibodies to gonococcal pili: studies on antigenic determinants on pili from variants of strain P9.

Several hybrid cell lines producing monoclonal antibodies against gonococcal pili have been derived. The reactivity of each antibody against variant pili of strain P9 was determined by ELISA. Using type-specific as well as broadly cross-reacting antibodies labelled with 125I, the capacity of unlabelled hybridoma antibodies to inhibit their attachment to various pilus types was determined. Some antibodies competed significantly and were judged to react at the same or closely positioned antigenic sites, whereas others bound non-competitively to the same pilus. These studies suggest the existence of distinct antigenic sites on gonococcal pili: a common antigenic region shared by all P9 pilus types and a type-specific region. Both antigenic sites contain more than one epitope.

Animals↗
PubMed1983

Antigenic cross-reactivity of Neisseria pili: investigations with type- and species-specific monoclonal antibodies.

Monoclonal antibodies have been produced with both type-specific and broadly cross-reacting properties against the variant pili of Neisseria gonorrhoeae P9. Competitive radioimmunoassays demonstrated that at least three separate epitopes contribute to type-specificity within the strain. ELISA using purified pili from clinical isolates showed that some of the type-specific epitopes are randomly distributed among variants of single strains isolated from different sites in sexual partners. Cross-reacting antibody SM1 recognized an epitope present on all gonococcal isolates. This epitope was also present on a large proportion of meningococci and could be directly demonstrated in CSF from a patient with meningococcal meningitis. Commensal Neisseria and other Gram-negative bacteria tested failed to react. The meningococci which lack the epitope recognized by the antibody SM1 were nevertheless shown by electron microscopy to be pilated, suggesting that pili from meningococci may be antigenically more diverse than those from gonococci.

Antibodies, Monoclonal↗
PubMed1982

Effect of anti-pilus antisera on virulence of variants of Neisseria gonorrhoeae for cultured epithelial cells.

Variants of Neisseria gonorrhoeae P9 possessing a, gamma or delta pili were shown to vary in their toxicity and virulence for human epithelial cells. Studies with antisera raised against purified pili showed that attachment and virulence were reduced to a significant degree in the presence of antisera to homologous pili. Heterologous antisera, while capable of agglutinating whole organisms, were largely ineffective in reducing attachment and cytotoxicity. Using an enzyme-linked immunosorbent assay (ELISA) system, the cross-reactivity between pili and heterologous antisera was estimated to be no more than 10-20%.

Antibodies↗
PubMed1981

Comparative virulence of opacity variants of Neisseria gonorrhoeae strain P9.

The invasive properties of nine variants of Neisseria gonorrhoeae strain P9 known to vary in their surface composition have been investigated. Relative virulence was evaluated by their cytotoxic effect on Chang epithelial cell monolayers. Piliated variants P9-2 (with alpha pili) and P9-20 (with beta pili plus protein II) showed increased ability to kill the target cells compared with the prototype P9-1 (lacking pili and additional outer membrane proteins). Two nonpiliated variants, P9-11 (with proteins IIa and IId) and P9-19 (with proteins II and IIc), were also relatively more virulent compared with P9-1. Enhanced attachment was exhibited by both piliated and some nonpiliated variants: beta-piliated P9-20 (with protein II; molecular weight, 29,000) and nonpiliated P9-16 (with protein IIb; molecular weight, 28,000) were the most effective in adherence to the target monolayers.

Animals↗
PubMed1980

Monoclonal immunoglobulin light chains in urine of patients with lymphoma.

Fourteen of 31 patients with non-Hodgkin's lymphoma or chronic lymphocytic leukaemia had a monoclonal immunoglobulin light chain detectable in their urine. These chains are believed to be synthesized by the B lymphoid cells comprising the tumour. Upon comparing the different cases, the occurrence and amount of monoclonal light chain showed no dependence upon the extent of tumour, the presence of leukaemic component, or exposure to cytotoxic therapy. The method of detection involved purifying the urinary light chains by immunosorption, and examining their electrophoretic distributions so as to distinguish between the homogeneous monoclonal chains and their heterogeneous normal analogues.

Adult↗
PubMed1979

Antibody-induced changes in levels of cyclic adenosine monophosphate in leukaemic lymphocytes.

When L2C leukaemic B lymphocytes from guinea-pigs were incubated in vitro with antibody directed to their surface immunoglobulin (Ig), a rapid rise in intracellular adenosine 3':5'-phosphate (cyclic adenosine monophosphate, cAMP) was observed. Estimation of cAMP was by a protein-binding assay using bovine adrenal protein kinase. Increases up to 30-fold occurred within 30 seconds of incubation at 37 degrees C, to be succeeded by a fall which reached the basal level between 5 and 7 min. The response was proportional to the amount of antibody present. Cross-linking of surface Ig by the antibody was necessary, bivalent (Fab'gamma)2 from the antibody gave a rise in cAMP similar to that given by the parent molecule, whereas monomeric Fab'gamma was ineffective unless it was subsequently cross-linked by anti-antibody. The rise was too rapid to have required capping of the surface Ig for its induction. Not all perturbations of the plasma membrane by antibody induce such a surge in cAMP, since anti-beta2 microglobulin, also reacting with the lymphocyte surface, failed to alter cAMP concentration. The results emphasize that immunotherapy can be influenced by antibody altering the metabolic activity of target cells, quite apart from activation of immunological cytotoxic pathways.

Animals↗