Functional and molecular aspects of interferon action in human natural killer cells and other leucocytes
Abstract: Interferons comprise a class of structurally related proteins which exert several regulatory effects in responsive cells. These effects include the establishment of an antiviral state, the inhibition of cellular proliferation and the alteration of different immune reactions. In particular, the IFN:s rapidly augment the lytic activity of the natural killer (NK) cells. In the present thesis, some of the functional and molecular mechanisms by which IFN:s act on NK cells and other leucocytes are studied. A good correlation is found between the ability of different tumor cell lines to induce IFN production among peripheral blood lymphocytes and their sensitivity to NK cell cytotoxicity, indicating that IFN might regulate the activity of NK cells through a positive feed-back mechanism. When studying the interaction between the NK cells and two target cell lines it is demonstrated that the two cell lines are not recognized by the same receptors. The augmentation of NK cell cytotoxicity by IFN is shown to involve both alteration of receptor structures on the NK cell and enhancement of steps in their lytic machinery. The effects of IFN on the synthesis of individual proteins is then studied by two-dimensional electrophoresis. It is demonstrated that IFN-a and IFN-ß within 1.5 hours induce the synthesis of nine proteins (Mf80, 75, 62, 58, 53, 38, 36, 33 and 30 kD) in human lymphocytes. Tne induction is dependent on a rapid de novo RNA synthesis, which is initiated less than 30 minutes after the addition of IFN. The expression of the nine proteins is well correlated to the development of augmented NK cell cytotoxicity. Four of the proteins (Mr 80, 62, 38 and 33 kD) are found to be expressed in a panel of ten hematopoetic and two anchorage-dependent cell lines, whereas the remaining proteins seem to be expressed in leucocytes only. IFN induce the synthesis of the same proteins in both purified large granular lymphocytes (responsible for the main NK cell activity in man), T cells and monocytes, demonstrating that the augmentation of NK cell activity does not involve the formation of unique 1NK-cel11 specific proteins. Rather, the augmentation of the lytic activity of both NK cells, cytotoxic T cells and monocytes seem to involve common stages in their lytic mechanisms. In contrast to IFN-a and IFN-ß, IFN-y, does not induce any detectable proteins in either NK cells or T cells. This lack of effect of IFN-y on the protein synthesis is not a general phenomenon, since the effects of IFN-a and IFN-y are similar 1n a glioma cell line. These results demonstrate that there exists at least one pathway to augment the NK cell cytotoxicity which does not involve the increased synthesis of the nine IFN-a/IFN-ß inducible proteins and indicates that either these proteins are mainly involved in other effects of IFN, or that the augmentation by IFN-a/IFN-ß and IFN-y involve different pathways. When the effects of IFN-a on the synthesis of membrane-associated proteins is studied, it is demonstrated that only the 80 kD IFN-a inducible protein is associated with the cell membrane. In addition, IFN-a seems to induce three additional, me mb rane-as so ci a ted proteins (Mr 94, 76 and 66 kD) which are not detected in whole cell lysates.
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