Abstract
We studied the capacity of glutaraldehyde-fixed Helicobacter pylori to stimulate natural killer (NK) cell activity. Bacteria were incubated overnight with peripheral blood lymphocytes enriched for large granular lymphocytes (LGL), the mediators of non-major histocompatibility complex-restricted cellular cytotoxicity. Then, the cytolytic activity of LGL was tested against various tumor target cells. We observed that efficient cytolytic activity was generated against resistant and nonresistant tumor target cell lines. Nine local clinical isolates of H. pylori and the reference strain NCTC 11637 were tested, and they all were equally effective in inducing NK cell activity. However, flagellin antigen, glycine extract, urease, and lipopolysaccharide prepared from H. pylori NCTC 11637 all failed to induce significant NK cell activity. The supernatants which were collected after coincubation of bacteria with LGL contained a factor(s) which could activate resting LGL into efficient cytolytic activity. The supernatants were also analyzed for interferon (IFN) activity. We observed that high titers of IFN were produced and that IFN activity was neutralized with anti-gamma interferon (IFN-gamma) antiserum, but not with anti-IFN-alpha antiserum. Thus, contact of lymphocytes with H. pylori leads to efficient stimulation of NK cell activity and the production of IFN-gamma.