Recently, the Histiocyte Society revised the diagnostic criteria for hemophagocytic lymphohistiocytosis (HLH) to include low or absent natural killer (NK) cell activity, according to local laboratory reference. The aim of this study was to establish reference interval for functional NK-cell activity in 63 healthy Korean individuals using a flow-cytometric assay. We used peripheral blood mononuclear cells (PBMCs) as effector cells and Fluorescein isothiocyanate-labeled K562 cells as target cells. NK-cell activity was calculated using the following equation: NK-cell activity (%) = (test lysis - spontaneous lysis) x 100/(maximum lysis - spontaneous lysis). NK-cell activity was analyzed in 13 known HLH patients and 16 suspected non-HLH patients using a flow-cytometric assay. The mean (+/-SD) cytotoxicity of PBMCs from healthy individuals was 20.9 +/- 5.3% and the reference interval was 11.8-31.9%. The mean NK-cell activity of HLH patients (8.3 +/- 8.9%) was significantly lower (P = 0.001) than that of non-HLH patients (20.1 +/- 7.8%). The sequential changes in NK-cell activity in the HLH group corresponded to clinical and laboratory findings following treatment. We successfully developed a functional NK-cell activity test for use in the clinical laboratory and obtained a reference interval of NK-cell activity from healthy donors. This assay, and associated reference interval, was used to analyze 30 clinically relevant specimens and the results were shown to be well correlated.

Background : Antimicrobial resistance of Helicobacter pylori is considered as the main cause of failure of eradication therapy. Because resistance to metronidazole has been reported in 25.8% to 66.2% of H. pylori, a combination of proton pump inhibitors (PPI), amoxicillin, and clarithromycin is currently recommended as a primary therapy. We investigated the prevalence of antimicrobial resistance to the primary drugs and the impact of antimicrobial resistance on eradication rates.Methods : Between May and August 2005, H. pylori isolates from 93 patients were tested for antimicrobial susceptibility at Asan Medical Center. Susceptibility tests of clarithromycin and amoxicillin were performed by the disk diffusion method and those of metronidazole and tetracycline by Etest (AB Biodisk, Solna, Sweden). The medical records of the patients were reviewed to collect the data such as demographic findings, previous and current eradication therapies, and bacteriological outcome. The appropriate therapy was defined as three-drug-combination including susceptible drugs only, or four-drug-combination including metronidazole in the case of metronidazole-resistance.Results : Resistance rates to clarithromycin and metronidazole were 17.2% and 33.3%, respectively, but there was no resistance to tetracycline and amoxicillin. The eradication was successful in 32 of the 36 patients (88.9%) who received the appropriate therapy, but none of 4 patients who received an inappropriate therapy (P<0.01).Conclusions : Resistance to clarithromycin seemed to increase and contribute to the failure of eradication therapy. For the appropriate therapy of H. pylori infection, the susceptibility results should be reported before initiation of the eradication therapy. (Korean J Lab Med 2006;26:179-84)