The effect of polymorphonuclear leucocyte (PMNL) factor on human natural killer (NK) cell activity in vitro

In a previous study [20] there was described the inhibitory effect of lysosomal proteins isolated from the guinea pig peritoneal exudate PMNL on the spontaneous cytotoxic activity of splenic cells in vitro. Moreover, in vivo investigations demonstrated these factors to inhibit also the development and activity of the antigen specific cytotoxic cells. The aim of the present study was to explain the role and mechanism of action of the PMNL factors in the regulation of the natural killer (NK) cell activity. The effect of PMNL factors on the NK cells was estimated in the tests based on 51Cr release using chick red blood cells CRBC). It was found that, similarly as in guinea pigs, the lysosomal proteins isolated from human peripheral blood PMNL exerted an inhibitory effect on the NK cells activity of human blood mononuclears against CRBC and this effect was independent of the activity of proteases present in the fractions of the studied lysosomal proteins. The inhibitory effect was not exerted by the factors released from the PMNL during their adherence. The obtained results seem to indicate that factors released from the PMNL during adherence are not identical to the substances released from the PMNL granules during their breakdown.