Validation of a Novel Immunoline Assay for Patient Stratification according to Virulence of the Infecting Helicobacter pylori Strain and Eradication Status.

Helicobacter pylori infection shows a worldwide prevalence of around 50%. However, only a minority of infected individuals develop clinical symptoms or diseases. The presence of H. pylori virulence factors, such as CagA and VacA, has been associated with disease development, but assessment of virulence factor presence requires gastric biopsies. Here, we evaluate the H. pylori recomLine test for risk stratification of infected patients by comparing the test score and immune recognition of type I or type II strains defined by the virulence factors CagA, VacA, GroEL, UreA, HcpC, and gGT with patient's disease status according to histology. Moreover, the immune responses of eradicated individuals from two different populations were analysed. Their immune response frequencies and intensities against all antigens except CagA declined below the detection limit. CagA was particularly long lasting in both independent populations. An isolated CagA band often represents past eradication with a likelihood of 88.7%. In addition, a high recomLine score was significantly associated with high-grade gastritis, atrophy, intestinal metaplasia, and gastric cancer. Thus, the recomLine is a sensitive and specific noninvasive test for detecting serum responses against H. pylori in actively infected and eradicated individuals. Moreover, it allows stratifying patients according to their disease state.

Helicobacter pylori FliD protein is a highly sensitive and specific marker for serologic diagnosis of H. pylori infection.

Screening for H. pylori in large populations continues to be a challenging task, since available tests have limited sensitivity and specificity, which, in population-based approaches, leads to significant numbers of false positive and false negative results. Various H. pylori proteins associated with virulence are highly immunogenic and therefore candidates to detect the infection. There are currently no defined markers that are recognized in all H. pylori infected patients and that do not show cross-reactivity with other bacterial proteins. We identified the H. pylori "hook-associated protein 2 homologue", FliD (UniProtKB/Swiss-Prot: P96786.4) as a novel marker of infection for serological analysis. The H. pylori FliD protein is an essential element in the assembly of the functional flagella. However, this virulence factor has not yet been tested as a diagnostic marker in serology. For this purpose FliD was recombinantly expressed in E. coli, purified by affinity chromatography and gel filtration and used to coat ELISA plates or immobilized on nitrocellulose stripes. To evaluate its antigenicity we screened a defined panel of patient sera. The recombinant H. pylori FliD protein reacted with a high percentage of human sera. Among 318 samples reported positive by histology, 310 (97.4%) were tested positive by FliD Line assay, and 165 out of 170 samples were tested positive by ELISA (97%). We could also reconfirm 297 out of 300 (99%) negative sera by Line assay and 73 from 76 (96%) by ELISA. Taken together, application of FliD in serological diagnosis of H. pylori infection presents a high specificity of up to 99% and a sensitivity of up to 97%. This makes especially the FliD ELISA a simple, cost effective and highly efficient tool to detect H. pylori infection in developing countries where prevalence is high and other screening methods are either not available or are unaffordable.

A novel line immunoassay based on recombinant virulence factors enables highly specific and sensitive serologic diagnosis of Helicobacter pylori infection.

Helicobacter pylori colonizes half of the world's population, and infection can lead to ulcers, gastric cancer, and mucosa-associated lymphoid tissue (MALT) lymphoma. Serology is the only test applicable for large-scale, population-based screening, but current tests are hampered by a lack of sensitivity and/or specificity. Also, no serologic test allows the differentiation of type I and type II strains, which is important for predicting the clinical outcome. H. pylori virulence factors have been associated with disease, but direct assessment of virulence factors requires invasive methods to obtain gastric biopsy specimens. Our work aimed at the development of a highly sensitive and specific, noninvasive serologic test to detect immune responses to important H. pylori virulence factors. This line immunoassay system (recomLine) is based on recombinant proteins. For this assay, six highly immunogenic virulence factors (CagA, VacA, GroEL, gGT, HcpC, and UreA) were expressed in Escherichia coli, purified, and immobilized to nitrocellulose membranes to detect serological immune responses in patient's sera. For the validation of the line assay, a cohort of 500 patients was screened, of which 290 (58.0%) were H. pylori negative and 210 (42.0%) were positive by histology. The assay showed sensitivity and specificity of 97.6% and 96.2%, respectively, compared to histology. In direct comparison to lysate blotting and enzyme-linked immunosorbent assay (ELISA), the recomLine assay had increased discriminatory power. For the assessment of individual risk for gastrointestinal disease, the test must be validated in a larger and defined patient cohort. Taking the data together, the recomLine assay provides a valuable tool for the diagnosis of H. pylori infection.