Clinical Relevance of the Helicobacter pylori gene for blood-group antigen-binding adhesin

1
Clinical Relevance of the Helicobacter pylori
gene for blood-group antigen-binding adhesin

• Gerhard, M., Lehn, N., et al. 1999
• Proceedings of the National Academy of Sciences
• Presented by
• Ria Achong

2
Helicobacter pylori as an etiologic agent

• Helicobacter pylori causes
• Gastric ulcers
• Duodenal ulcers
• Adenocarcinomas of the distal stomach
• Gastric musosa associated lymphoid tissue (MALT)
  lymphomas

3
Genomic basis for pathogenesis

• Some genes associated with Hp
• VacA pore-forming, vaculating cytotoxin
• CagA highly associated with virulence
• stimulates immune response
• BabA Lewisb antigen adhesin

4
Clinical importance of genome

• Type 1 Hp strain
• VacA and CagA
• more virulent strain
• BabA
• may contribute further to pathogenicity through
  specific tropism (gastric epithelial adhesion)

5
Rationale

• To determine the clinical importance of the babA
  gene to the virulence of Helicobacter pylori
  strains and, thus, the development of the four
  diseases caused by Hp

6
Materials/Methods

• Obtained Hp isolates from 114 infected patients
• Patient disease distribution
• Distal gastric carcinoma n27
• Duodenal ulcer n23
• Gastric mucosa associated lymphoid tissue (MALT)
  lymphoma n29
• Antral gastritis n35
• Cultured Hp isolates

7
Materials/Methods

• Tested gastric tissue samples from patients for
  the presence of Lewisb antigens
• Performed in vitro adherence assay (binding of
  bacteria to Lewisb antigens)
• Coat plates with Lewisb antigens conjugated to
  human serum albumin
• Add bacterial suspension and incubate

8
Materials/Methods

• Isolated DNA and RNA from Hp cultures
• Used reverse transcriptase and PCR to amplify the
  extracted DNA and RNA to locate the babA gene
• Prior, babA had been cloned babA2
• Identified presence of babA in isolates by
  comparison to babA2 sequence

9
Results

• Using the PCR technique
• 82 out of 114 isolates (71.9) were identified as
  babA2

10
Correlation between babA2 genotype and Lewisb
epitope adherence
Lewisb epitope adherence babA2- (n23 strains) babA2 (n31 strains)
Lewisb adhesion 0 28
No Lewisb adhesion 23 3
Correlation 100 91
Out of 114 isolates, subset of 54 strains used
11
Frequency and correlation of the vacAs1, cagA,
and babA2 genotypes
Genotype (n114) babA2 (n82) babA2- (n32) c2 value (babA2) P value (babA2)
vacAs1 (n99) 78 21 17.5 lt0.01
cagA (n86) 70 16 15.3 lt0.01
Type 1 (n84) (cagA vacAs1) 68 16 12.8 lt0.01
12
Correlation between virulence factor genotypes
and disease prevalence ()
Gene Total n114 GA n27 DU n23 MALT n29 Gast. n35 P value GA P value DU
vacAs1 86.8 96.3 100 72.4 82.9 .126 .036
vacAs2 13.2 3.7 0 27.6 17.1 - -
vacAm1 47.4 74.1 34.7 34.5 45.7 .025 -
vacAm2 52.6 25.9 65.2 65.5 54.3 - -
cagA 78.9 92.6 100 48.3 77.1 .094 .008
babA2 71.9 77.8 100 69.0 51.4 .033 .0002
Type 1 73.7 85.1 100 41.4 71.4 .235 .0041
Triple 59.6 74.1 100 34.5 42.9 .014 2x10-6
Type 1 vacA and cagA Triple Positive
vacA, cagA, babA2
Significant - Highly significant -
13
Comparison of Type 1 and Triple genotype and
disease prevalence
Type 1 vacA and cagA Triple Positive
vacA, cagA, babA2
14
Conclusion
15
Importance of babA for adhesion

• babA is required for adhesion to the Lewisb
  antigens on the gastric epithelium
• Thus, presence of babA is good indicator of
  bacterial ability to express Lewisb binding
  proteins and thus, to bind to epithelial cells

16
babA and duodenal ulcers

• babA2 genotype is a good marker for the presence
  of duodenal ulcers
• Thus, the babA adhesin and Lewisb antigens play a
  central role in the pathogenesis of Hp and ulcer
  disease

17
babA and duodenal ulcers

• Reason
• Hp induces occurrence of metaplasia (replacement
  of one cell type by another)
• Thus, duodenum contains gastric metaplasia
• Hp can bind directly to the gastric epithelium in
  intestine
• Hp causes the destruction and thus erosion of the
  epithelium of the intestinal walls (i.e. ulcers)

18
babA and gastric adenocarcinomas

• babA2 genotype is a also good marker for the
  presence of gastric cancer
• Thus, babA adhesin and Lewisb antigens play an
  important role in the pathogenesis of Hp and
  gastric cancer

19
babA and gastric adenocarcinomas

• Reason
• Hp induces occurrence of metaplasia
• Thus, stomach contains intestinal metaplasia
• Hp can bind directly to the intestinal
  epithelium in the stomach
• Intestinal metaplasia is a potential precursor
  for gastric cancer
• Thus, Hp may be important for the development of
  distal gastric cancer

20
Clinical importance of babA

• babA, in association with vacA and cagA, may play
  a critical role in mediating Hp pathogenesis
• NB the significant correlation of triple and
  gastric adenocarcinoma (GA) as opposed to the
  nonsignificant correlation of type 1 and GA

Gene Total n114 GA n27 P value GA
Type 1 73.7 85.1 .235
Triple 59.6 74.1 .014
21
Treatment of Hp

• Thus, triple strains of Helicobacter pylori in
  patients should be eradicated to prevent the
  possible development of duodenal ulcers and
  gastric adenocarcinomas