The Helicobacter pylori CagY Protein Drives Gastric Th1 and Th17 Inflammation and B Cell Proliferation in Gastric MALT Lymphoma

Abstract

Background: the neoplastic B cells of the Helicobacter pylori-related low-grade gastric mucosa-associated lymphoid tissue (MALT) lymphoma proliferate in response to H. pylori, however, the nature of the H. pylori antigen responsible for proliferation is still unknown. The purpose of the study was to dissect whether CagY might be the H. pylori antigen able to drive B cell proliferation.

Methods: the B cells and the clonal progeny of T cells from the gastric mucosa of five patients with MALT lymphoma were compared with those of T cell clones obtained from five H. pylori-infected patients with chronic gastritis. The T cell clones were assessed for their specificity to H. pylori CagY, cytokine profile and helper function for B cell proliferation.

Results: 22 of 158 CD4⁺ (13.9%) gastric clones from MALT lymphoma and three of 179 CD4⁺ (1.7%) clones from chronic gastritis recognized CagY. CagY predominantly drives Interferon-gamma (IFN-γ) and Interleukin-17 (IL-17) secretion by gastric CD4⁺ T cells from H. pylori-infected patients with low-grade gastric MALT lymphoma. All MALT lymphoma-derived clones dose dependently increased their B cell help, whereas clones from chronic gastritis lost helper activity at T-to-B-cell ratios greater than 1.

Conclusion: the results obtained indicate that CagY drives both B cell proliferation and T cell activation in gastric MALT lymphomas.

Keywords: B cells; CagY; Helicobacter pylori; MALT; T cells; cytokines; gastric lymphoma.

Figure 1

Antigen specificity of H. pylori-reactive T cell clones derived from the gastric mucosa of H. pylori-infected patients with low-grade MALT B cell lymphoma (MALT) or uncomplicated chronic gastritis (CG). In vivo activated T cells were recovered from biopsy specimens of gastric mucosa and cloned by limiting dilution. T cell blasts from each clone were seeded in triplicate cultures with irradiated autologous peripheral blood mononuclear cells in the presence of medium alone or optimal doses of H. pylori lysate (10 μg/mL), or CagY (1 μg/mL). After 60 h, [³H] thymidine uptake was measured and expressed as mitogenic index. A significant difference (*) was found between the mitogenic index of CagY-specific MALT lymphoma-derived T clones and CG-derived ones. A highly significant (***) proliferation to CagY than to H.pylori lysate was found in MALT lymphoma-derived T clones.

Figure 2

Cytokine profile of gastric mucosa CagY-specific CD4⁺ T cell clones obtained from H. pylori-infected patients with gastric low-grade MALT lymphoma. Th clones were tested for cytokine production (A,B). CagY-specific Th clones were stimulated with CagY and TNF-α and IL-4, IFN-γ and IL-17 production was measured in culture supernatants. In unstimulated cultures, levels of TNF-α, IL-4, IFN-γ and IL-17 were consistently < 20 pg/mL. CD4⁺ T cell clones producing IFN-γ, but not IL-17 nor IL-4, were coded as Th1. CD4⁺ T cell clones producing IL-17, but not IFN-γ nor IL-4, were coded as Th17. CD4⁺ T cell clones producing IFN-γ, and IL-17, but not IL-4, were coded as Th17/Th1. CD4⁺ T cell clones producing TNF-α and IL-4, but not IL-17, were coded as Th0.

Figure 3

B cell proliferation to CagY. CagY-stimulated T cell clones derived from the gastric mucosa of patients with MALT lymphoma provide huge help for proliferation to autologous B cells (A). Irradiated T cell blasts of each CagY-reactive clone derived from patients with gastric MALT lymphoma or chronic gastritis were co-cultured for four days with peripheral blood autologous B cells (3 × 10⁴) at 0.2, 1, and 5 to 1 T-to-B-cell ratios in the presence of medium alone or CagY. Sixteen hours before harvesting, 0.5 μCi of [³H] thymidine was added, and its uptake was measured as mitogenic index. B cells cultured with or without CagY did not show any proliferation both in gastric low-grade MALT lymphoma and chronic gastritis patients at any CagY concentration used (0.1, 1, 10 μg/mL) (B). B cells cultured without CagY, with autologous irradiated gastric T cells did not show any proliferation both in gastric low-grade MALT lymphoma and in chronic gastritis patients at any T-to-B-cell ratios (0.2, 1, and 5 to 1) (C). * p < 0.05; *** p < 0.001.