Helicobacter pylori outer membrane protein 18 (Hp1125) induces dendritic cell maturation and function

Dendritic cells (DCs) are potent antigen-presenting cells that initiate T-cell responses. A robust adaptive Th1 immune response is crucial to an adaptive (Th2) immune response necessary for vaccine-induced protective immunity against Helicobacter pylori. It has been shown that several outer membrane proteins (Omps) induce a robust antibody response. However, it is also known that the antibodies generated are not protective. Moreover there is great variation in the recognition of high molecular weight H. pylori proteins by sera from infected patients. In contrast to the high molecular weight proteins, serologic responses to small molecular weight proteins provide assessment of current infection with H. pylori and also of its eradication.

The goal of the study was to analyze the activation of the immune response by a specific low molecular weight Omp that is universally expressed by all H. pylori strains. Therefore, we studied interaction of H. pylori Omp18 with DCs.

Activation of murine bone marrow-derived DCs and production of cytokines by Omp18 was assessed by fluorescence-activated cell sorter (FACS) for costimulatory markers and ELISA, respectively. The ability of Omp18 stimulated DCs to induce lymphocyte proliferation was measured in a mixed leukocyte reaction.

Omp18 induced higher expression of the B7 (CD80 and CD86) costimulatory molecule after 18 hours indicating processing and presentation of the antigen on the surface by bone marrow-derived DCs. The maturing DCs also secreted significant levels of IL-12, but was 4-fold less than that stimulated by whole bacteria. Omp18-primed DCs induced proliferation and release of IFNgamma by syngeneic splenocytes.

We concluded that Omp18 is capable of activating DCs initiating a Th1 immune response.