Neutrophils as a source of putative restriction proteases: degradation of mammalian and yeast proteins monitored by two-dimensional gel electrophoresis.

Abstract

We have compared the ability of intact neutrophils to degrade a complex substrate of proteins from mammalian and yeast origin. The substrate was obtained by biosynthetic labeling, and subsequent lysis of K562 cells (leukemic cell line) and of yeast culture. The mammalian substrate consisted of 619 and the yeast substrate of 185 different polypeptides, as visualized and represented on two-dimensional gel patterns. Upon incubation of the mammalian substrate with neutrophils, the bulk of spots disappeared so rapidly that after 240 min of incubation only 21 spots were detectable. Just one spot remained unaltered in its intensity throughout the whole period of incubation. About 440 spots reveal a t1/2 shorter than 8 min. Yeast substrate is represented by a smaller number of the starting polypeptides (185) from which 55 spots "survive" the neutrophil treatment. About 30 spots have a t1/2 shorter than 8 min. We conclude that neutrophils are equipped with a potent proteolytic apparatus, and this is capable of eliminating various proteins in a highly efficient manner. The system is much less effective in eliminating proteins from distant species, like yeast. Although the cells governing and regulating the immune system are clearly of lymphoid origin, it might well be that the preimmune task of eliminating self antigens in a manner as predicted in the restriction protease hypothesis is performed by neutrophils.