Infection with Helicobacter pylori cytotoxin-associated gene A (CagA)-positive strains is associated with the development of gastric cancer (GC). However, some reports have failed to demonstrate an increased frequency of CagA antibodies in GC patients. This study evaluated the response of IgG antibody and subclasses IgG1 and IgG2 against both CagA and H. pylori membrane antigens in patients with pre-cancerous lesions and cases with GC. A total of 137 patients with a positive serum IgG response to H. pylori were selected: 46 with intestinal metaplasia, 41 with gastric adenocarcinoma and 50 with non-atrophic gastritis (NAG) considered as controls. The response of total IgG, IgG1 and IgG2 was investigated by immunoblot and ELISA using an in-house recombinant CagA and membrane antigens from a local strain, and possible associations were estimated using a logistic regression model. Compared with NAG patients, GC patients showed a higher frequency of IgG2 CagA antibodies (55.2 vs 15.4 %, P50.001), but a lower frequency (80.5 vs 96.0 %, P50.021) and diminished levels of IgG2 H. pylori antibodies [12.5 vs 21.9 ELISA units (EU), P50.007]. GC patients also presented lower levels of CagA (32.6 vs 42.4 EU, P50.004) and H. pylori total IgG (33.7 vs 38.7 EU, P50.029). GC was associated with a positive IgG2 CagA response [odds ratio (OR)53.74, 95 % confidence interval (CI) 1.81-5.37; P50.002] and with a low titre of total IgG CagA antibodies (OR52.18, 95 % CI 1.35-2.69; P50.006). These results suggest that the IgG2 response to CagA could be used as a novel serological marker to identify patients with H. pylori-associated GC.
INTRODUCTIONAccording to estimations based on seroprevalence studies, half of the world population is infected with Helicobacter pylori (Brown, 2000). In 1994, the International Agency for Research on Cancer classified H. pylori as a class 1 human carcinogen (IARC Working Group, 1994). As reported by meta-analyses, a two-to threefold increased risk of stomach cancer is associated with this infection (Huang et al., 1998;Eslick et al., 1999). Gastric malignancy is the fourth most common type of cancer and the second most common cause of cancer-related deaths worldwide (Parkin et al., 2005). H. pylori infection induces a chronic inflammation of the gastric mucosa that is intensified by high levels of proinflammatory cytokines during the immune response, especially in the case of strains possessing the cagA gene (Peek et al., 1995; Yamaoka et al., 1997). In a small proportion of infected individuals and over a decades-long process, this chronic inflammation leads to the development of gastric cancer (GC) through a series of progressive stages that include non-atrophic gastritis (NAG), atrophic gastritis, metaplasia and dysplasia (Correa, 1996).The cagA gene of H. pylori is located in the cag pathogenicity island (cag-PAI). The CagA toxin is injected into the gastric Abbreviations: cagA, cytotoxin-associated gene A; cag-PAI, cag pathogenicity island; CI, confidence interval; DC, dendritic cell; EU, ELISA units;...