Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 9 2 2017 08 12 97 102 EN Hashem Fakhre-Yaseri Gastroenterology, Research Center for Gastroenterology and Liver Diseases, Firoozgar Hospital, Iran University of Medical Sciences, Tehran, Iran AND Department of Internal Medicine, Firoozgar Hospital, Iran University of Medical Sciences, Tehran, Iran Ali Baradaran-Moghaddam Department of Microbiology, School of Medicine, Iran University of Medical Sciences, Tehran, Iran Mehdi Shekaraby Immunology Research Center, Iran University of Medical Sciences, Tehran, Iran AND Department of Immunology, School of Medicine, Iran University of Medical Sciences, Tehran, Iran Hamid Reza Baradaran Department of Epidemiology, Iran University of Medical Sciences, Tehran, Iran Seyed Kamran Soltani-Arabshahi Department of Internal Medicine, Firoozgar Hospital, Iran University of Medical Sciences, Tehran, Iran 2015 11 30 2017 06 16 Background and Objectives: The cytotoxin-associated gene (cag) pathogenicity island is reported to be a major virulence factor of Helicobacter pylori infection. It is previously reported that the cagA-positive strains are more virulent, so it can be postulated that the cagA-positive gastritis will be more severe and the serum immunoglobulin G (IgG) and A (IgA) anti-CagA antibody titer will be higher. The aim of this study was to compare the relationship between IgG and IgA anti-CagA antibody and the cagA gene expression in patients with dyspepsia. Serum samples obtained from 130 dyspeptic patients with positive H. pylori in histological and Geimsa staining were tested for serum IgG and IgA anti-CagA antibody using the enzyme-linked immunosorbent Assay. The expression of the cagA gene was determined using PCR on the biopsy samples, taken via endoscopy. Results: In our material, the sensitivity of IgG anti-CagA antibody in identifying patients with a proven infection with the cagA-positive strains was 97.67%, and the negative likelihood ratios was 0.06. There was not significant correlation between serum IgA anti-CagA and the expression of the cagA gene among the dyspeptic patients. Conclusion: The IgG antibody titer was significantly higher in our patients with the cagA-positive H. pylori strain. However, in daily practice, the level of the IgG antibody titer cannot predict whether or not an individual carries a cagA-positive H. pylori strain, because there is a major overlap in the IgG antibody titer between the cagA-positive and cagA-negative patients.   https://ijm.tums.ac.ir/index.php/ijm/article/view/827 https://ijm.tums.ac.ir/index.php/ijm/article/download/827/715