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Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening disease associated with immune system hyperactivation and the appearance of serious systemic disturbances. The purpose of this study was an assessment of natural killer (NK) cell disturbances in a group of children with clinical signs of HLH. A total of 43 children with HLH and 17 healthy children were enrolled in the study. NK phenotyping, intracellular perforin staining, and cytotoxicity tests were performed by using the flow cytometry method. HLH patients were divided into 6 HLH types: 9% infection-related HLH; 7% malignancy-related HLH; 21% macrophage activating syndrome; 12% familial hemophagocytic lymphohistiocytosis; 2% X-linked lymphoproliferative syndrome; and 49% as HLH of unknown background. A positive correlation was observed between cytotoxicity and NK cells in children with HLH (P=0.01). In all HLH groups, the percentage of NK cells was significantly lower than in the control population. The spontaneous cytotoxicity was significantly lower in HLH patients. The results presented in this study indicate the importance of impaired function and the number of NK cells in the pathogenesis of HLH. Nonetheless, the background of disturbances seems to be different in various cases.

The aim of this study was to analyse whether split influenza vaccine may elicit NK cytotoxic response in the vaccinated elderly people and whether this effect may be maintained over few weeks after vaccination. It was also worth investigating the relation between NK activity in the vaccinated and specific immune protection against influenza and non-specific against other infections. Two groups of volunteers were vaccinated with trivalent split viron influenza vaccine in two consecutive seasons (1999/2000; 2000/2001). The elderly group consisted of 142 people (65-92 years old) in the first season and 110 in the second; while the young (16-44 years old) of 98 and 67 people, respectively. An analysis of NK cytotoxic activity had been done before vaccination, two days, one month and fifth months thereafter. The results revealed that vaccination with the influenza vaccine had an augmenting effect on NK activity, in all groups examined, in both epidemic seasons, visible at two days and 1 month after the vaccination. In the elderly high pre- and post-vaccination NK activity was related to higher titers of anti-hemagglutinin, better health status and lower incidence of all cause respiratory tract infections. At the second vaccination, most of the elderly with chronic medical conditions and high NK activity, who did not attain the protective level of anti-hemagglutinins in the first season, converted into the protected. High pre- and post-vaccination NK activity predisposes elderly people to the protective humoral anti-hemagglutinin response and gives better protection from respiratory tract infections.