Natural killing can be independent of interferon generated in vitro

Influenza viral glycoproteins induced cell-mediated cytotoxicity by an interferon-independent mechanism

Human natural killer (NK) cells exposed to the influenza surface antigen neuraminidase (NA) show high cytotoxic activity, as evaluated using chromium-labeled K562 target cells in a standard overnight cytotoxicity assay. The role of interferon (IFN) in the stimulation of NK cells was examined by using three separate approaches. The use of appropriate antibodies to check IFN- and NA-specific cell-mediated cytotoxicity (CMC) stimulation showed that antibodies to IFN (-alpha, -gamma) did not alter NA-induced CMC, and vice versa. The treatment of NK cells with actinomycin D, before or after stimulation with IFN and NA revealed that only IFN-induced CMC was inhibited (50 to 100%). However, NK cells that were stimulated with NA before their exposure to actinomycin D became susceptible to stimulation by IFN. The interaction kinetics between IFN and NA demonstrated the presence of two mechanisms of CMC stimulation. Taken together, the results clearly show that stimulation of CMC by a viral component is effected through an IFN-independent pathway, and that this mechanism is probably followed by IFN under certain conditions.

In vitro enhancement of human natural cell-mediated cytotoxicity by purified influenza virus glycoproteins

The role of the glycoproteins of influenza virus, hemagglutinin (HA), and neuraminidase (NA) in the in vitro stimulation of natural cell-mediated cytotoxicity (NCMC) or natural killer activity of human peripheral blood lymphocytes was evaluated with radiolabeled K562 cells as target cells in an overnight chromium release assay. Three different approaches were used. (i) Purified viral proteins were obtained by extraction with Nonidet P-40, separation on a sucrose gradient, and further purification by affinity chromatography. Ficoll-Hypaque-purified peripheral blood lymphocytes exposed to HA or NA individually or to a mixture of both significantly increased NCMC (32 to 50%). (ii) Treatment of HA and NA with their respective homologous antisera or F(ab')2 antibody abrogated the stimulation of NCMC by these glycoproteins. (iii) Virions treated with proteolytic enzymes resulted in viral cores lacking either HA or NA or both activities. Compared to whole virions, viral cores devoid of HA activity only induced a 50% increase in NCMC, whereas viral cores lacking HA activity and with traces of NA activity stimulated only 10% of the NCMC. These results suggest that influenza virus-induced cell-mediated cytotoxicity is largely due to its glycoproteins.

Studies of interferon production and natural killing by lymphocytes from multiple sclerosis patients

Peripheral blood lymphocytes from patients with multiple sclerosis (MS) have been shown by numerous investigators to function abnormally in a variety of immunological tests in vitro. In this article, data concerning defective natural killer (NK) cell function and interferon production by MS patients' lymphocytes have been reviewed. Production of IFN-alpha and IFN-gamma by appropriately stimulated lymphocytes has been shown to be significantly reduced in many patients with acute remitting or chronic progressive disease. Furthermore, a significant proportion of these patients has been found to exhibit reduced levels of endogenous and augmented NK cell activity. A likely explanation for these phenomena is that altered traffic occurring as a consequence of disease has led to a relative loss of NK and IFN-producing cells from the peripheral circulation. Flow cytometric data obtained using monoclonal antibodies that selectively label these effector populations were presented. Possible explanations for the observed defects and their significance relative to our understanding of the etiopathogenesis of MS were discussed.