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Selective inhibition of Ii-dependent antigen presentation by Helicobacter pylori toxin VacA.

Molinari M, Salio M, Galli C, Norais N, Rappuoli R, Lanzavecchia A, Montecucco C - J. Exp. Med. (1998)

Bottom Line: Its role in the chronic infection established by H. pylori is unknown.We found that VacA interferes with proteolytic processing of tetanus toxin and toxoid and specifically inhibits the Ii-dependent pathway of antigen presentation mediated by newly synthesized major histocompatibility complex (MHC) class II, while leaving unaffected the presentation pathway dependent on recycling MHC class II.The results presented here suggest that VacA may contribute to the persistence of H. pylori by interfering with protective immunity and that this toxin is a new useful tool in the study of the different pathways of antigen presentation.

View Article: PubMed Central - PubMed

Affiliation: Centro CNR Biomembrane and Dipartimento di Scienze Biomediche, Università di Padova, 35121 Padova, Italy.

ABSTRACT
A major virulence factor in the stomach chronic infection by Helicobacter pylori is a protein toxin (VacA), which alters cell membrane trafficking of late endosomal/prelysosomal compartments. Its role in the chronic infection established by H. pylori is unknown. To test the possibility that VacA alters antigen processing taking place in prelysosomal compartments, we have used the well-established model of antigen processing and presentation consisting of tetanus toxoid-specific human (CD4(+)) T cells stimulated by autologous antigen-pulsed Epstein-Barr virus-transformed B cells. We found that VacA interferes with proteolytic processing of tetanus toxin and toxoid and specifically inhibits the Ii-dependent pathway of antigen presentation mediated by newly synthesized major histocompatibility complex (MHC) class II, while leaving unaffected the presentation pathway dependent on recycling MHC class II. The results presented here suggest that VacA may contribute to the persistence of H. pylori by interfering with protective immunity and that this toxin is a new useful tool in the study of the different pathways of antigen presentation.

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Effect of VacA on  the proteolytic processing of 125I-TeNT by EBV-B cell clones. (a)  125I-TeNT–derived TCA-soluble radioactive peptides released  in the culture medium by cells  exposed to increasing VacA concentrations. After incubation  with 250 nM VacA, the two  APC clones release in the medium ∼40% of the TCA-soluble radioactivity released by control cells. ANT– and KS–EBV-B  internalize antigens via fluid  phase endocytosis, but parallel  experiments with clones Fc4m  and Fc7, which internalize antigen via surface Ig, gave similar  results (see Table 1). Values are  representative of sets of at least  three independent experiments. (b) Left, control cells; right, VacA-treated  cells. The pattern of gel-associated radioactivity determined by densitometric scanning of an autoradiogram shows differences in 125I-TeNT  processing, after VacA-treatment of the TT-specific EBV-B cell clone  Fc4m; the ratio between peaks a and b (control cells) changes upon treatment of the APCs with VacA (a′ and b′ in VacA-treated cells); fragment c  is not formed in cells treated with the toxin, whereas formation of peaks  d′ and e′ increases with respect to control cells.
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Figure 1: Effect of VacA on the proteolytic processing of 125I-TeNT by EBV-B cell clones. (a) 125I-TeNT–derived TCA-soluble radioactive peptides released in the culture medium by cells exposed to increasing VacA concentrations. After incubation with 250 nM VacA, the two APC clones release in the medium ∼40% of the TCA-soluble radioactivity released by control cells. ANT– and KS–EBV-B internalize antigens via fluid phase endocytosis, but parallel experiments with clones Fc4m and Fc7, which internalize antigen via surface Ig, gave similar results (see Table 1). Values are representative of sets of at least three independent experiments. (b) Left, control cells; right, VacA-treated cells. The pattern of gel-associated radioactivity determined by densitometric scanning of an autoradiogram shows differences in 125I-TeNT processing, after VacA-treatment of the TT-specific EBV-B cell clone Fc4m; the ratio between peaks a and b (control cells) changes upon treatment of the APCs with VacA (a′ and b′ in VacA-treated cells); fragment c is not formed in cells treated with the toxin, whereas formation of peaks d′ and e′ increases with respect to control cells.

Mentions: Cells were washed and resuspended to a density of 106 cells/ml in culture medium supplemented with 2% FCS. Highly purified toxin (VacA) of H. pylori, strain CCUG17874, was added. After 4 h of incubation at 37°C, cells were washed, resuspended (106 cells/ml) in culture medium supplemented with 10% FCS, and pulsed for an additional 4 h at 37°C with the antigens tetanus toxin (TeNT), recombinant human epidermal growth factor (EGF; Sigma Chemical Co., St. Louis, MO) and TT (Chiron Vaccines, Siena, Italy). Radioactive antigens 125I-TeNT, labeled with Bolton-Hunter reagent (Amersham Internatioanl, Little Chalfont, UK), and 125I-EGF, labeled with Iodo-Gen (Sigma Chemical Co.) were used for the experiments reported in Fig. 1 and Table 1.


Selective inhibition of Ii-dependent antigen presentation by Helicobacter pylori toxin VacA.

Molinari M, Salio M, Galli C, Norais N, Rappuoli R, Lanzavecchia A, Montecucco C - J. Exp. Med. (1998)

Effect of VacA on  the proteolytic processing of 125I-TeNT by EBV-B cell clones. (a)  125I-TeNT–derived TCA-soluble radioactive peptides released  in the culture medium by cells  exposed to increasing VacA concentrations. After incubation  with 250 nM VacA, the two  APC clones release in the medium ∼40% of the TCA-soluble radioactivity released by control cells. ANT– and KS–EBV-B  internalize antigens via fluid  phase endocytosis, but parallel  experiments with clones Fc4m  and Fc7, which internalize antigen via surface Ig, gave similar  results (see Table 1). Values are  representative of sets of at least  three independent experiments. (b) Left, control cells; right, VacA-treated  cells. The pattern of gel-associated radioactivity determined by densitometric scanning of an autoradiogram shows differences in 125I-TeNT  processing, after VacA-treatment of the TT-specific EBV-B cell clone  Fc4m; the ratio between peaks a and b (control cells) changes upon treatment of the APCs with VacA (a′ and b′ in VacA-treated cells); fragment c  is not formed in cells treated with the toxin, whereas formation of peaks  d′ and e′ increases with respect to control cells.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2199184&req=5

Figure 1: Effect of VacA on the proteolytic processing of 125I-TeNT by EBV-B cell clones. (a) 125I-TeNT–derived TCA-soluble radioactive peptides released in the culture medium by cells exposed to increasing VacA concentrations. After incubation with 250 nM VacA, the two APC clones release in the medium ∼40% of the TCA-soluble radioactivity released by control cells. ANT– and KS–EBV-B internalize antigens via fluid phase endocytosis, but parallel experiments with clones Fc4m and Fc7, which internalize antigen via surface Ig, gave similar results (see Table 1). Values are representative of sets of at least three independent experiments. (b) Left, control cells; right, VacA-treated cells. The pattern of gel-associated radioactivity determined by densitometric scanning of an autoradiogram shows differences in 125I-TeNT processing, after VacA-treatment of the TT-specific EBV-B cell clone Fc4m; the ratio between peaks a and b (control cells) changes upon treatment of the APCs with VacA (a′ and b′ in VacA-treated cells); fragment c is not formed in cells treated with the toxin, whereas formation of peaks d′ and e′ increases with respect to control cells.
Mentions: Cells were washed and resuspended to a density of 106 cells/ml in culture medium supplemented with 2% FCS. Highly purified toxin (VacA) of H. pylori, strain CCUG17874, was added. After 4 h of incubation at 37°C, cells were washed, resuspended (106 cells/ml) in culture medium supplemented with 10% FCS, and pulsed for an additional 4 h at 37°C with the antigens tetanus toxin (TeNT), recombinant human epidermal growth factor (EGF; Sigma Chemical Co., St. Louis, MO) and TT (Chiron Vaccines, Siena, Italy). Radioactive antigens 125I-TeNT, labeled with Bolton-Hunter reagent (Amersham Internatioanl, Little Chalfont, UK), and 125I-EGF, labeled with Iodo-Gen (Sigma Chemical Co.) were used for the experiments reported in Fig. 1 and Table 1.

Bottom Line: Its role in the chronic infection established by H. pylori is unknown.We found that VacA interferes with proteolytic processing of tetanus toxin and toxoid and specifically inhibits the Ii-dependent pathway of antigen presentation mediated by newly synthesized major histocompatibility complex (MHC) class II, while leaving unaffected the presentation pathway dependent on recycling MHC class II.The results presented here suggest that VacA may contribute to the persistence of H. pylori by interfering with protective immunity and that this toxin is a new useful tool in the study of the different pathways of antigen presentation.

View Article: PubMed Central - PubMed

Affiliation: Centro CNR Biomembrane and Dipartimento di Scienze Biomediche, Università di Padova, 35121 Padova, Italy.

ABSTRACT
A major virulence factor in the stomach chronic infection by Helicobacter pylori is a protein toxin (VacA), which alters cell membrane trafficking of late endosomal/prelysosomal compartments. Its role in the chronic infection established by H. pylori is unknown. To test the possibility that VacA alters antigen processing taking place in prelysosomal compartments, we have used the well-established model of antigen processing and presentation consisting of tetanus toxoid-specific human (CD4(+)) T cells stimulated by autologous antigen-pulsed Epstein-Barr virus-transformed B cells. We found that VacA interferes with proteolytic processing of tetanus toxin and toxoid and specifically inhibits the Ii-dependent pathway of antigen presentation mediated by newly synthesized major histocompatibility complex (MHC) class II, while leaving unaffected the presentation pathway dependent on recycling MHC class II. The results presented here suggest that VacA may contribute to the persistence of H. pylori by interfering with protective immunity and that this toxin is a new useful tool in the study of the different pathways of antigen presentation.

Show MeSH
Related in: MedlinePlus