Lysosomal granules of rabbit exudate polymorphonuclear (PMN) leucocytes were isolated and then lysed by freezing-thawing. Topical application of this material to rat and rabbit mesentery produced sticking and emigration of leucocytes, stasis of blood flow, and petechial hemorrhage. The granule-free, supernatant fraction of the homogenized leucocytes failed to produce any of these reactions.

Cationic proteins extracted from these granules by weak acid and precipitated by ethanol at concentrations of 20 and 45 per cent, were also tested on heterologous, homologous, and autologous mesenteric vessels. The 20 per cent ethanol-precipitated fraction produced all of the aforementioned injury reactions, whereas the 45 per cent fraction was inactive. The intensity of inflammatory changes produced by the active cationic protein fraction was greater than that produced by lysed whole granules.

Both the 20 per cent and 45 per cent ethanol fractions of cationic protein induced clumping of rabbit platelets, in vitro.

The 20 per cent ethanol fraction also caused a slight acceleration in rate of swelling of isolated rabbit liver mitochondria.

The active material proved to be non-pyrogenic in rabbits.

This material exhibited no kinin-like effects when tested on isolated smooth muscle preparations (rabbit aorta and guinea pig ileum). In the rat, the protein produced a transient vasodepression which was inhibited by pretreatment of the animal with an antihistamine.

Ultraviolet absorption data and ribose assays showed that the 20 per cent ethanol fraction contained only 4 per cent or less of ribonucleic acid. Upon electrophoresis in starch gel, using acid buffer, this fraction separated into at least three major components which migrated towards the cathode.

Precipitation of one of the slowly migrating components by titration of the fraction to pH 10.5 greatly increased the inflammatory activity of the material.

The inflammatory basic protein fraction was essentially devoid of acid phosphatase, beta glucuronidase, acid ribonuclease, lysozyme, and catalase activity. The non-inflammatory basic protein fraction contained appreciable quantities of acid ribonuclease and lysozyme.

The foregoing data demonstrate that certain of the cationic proteins present in lysosomes of rabbit exudate PMN leucocytes can reproduce one of the cardinal features of the inflammatory response; namely, adhesion and emigration of leucocytes in the microcirculation. These findings offer fresh support for the role of lysosomes in the pathogenesis of tissue injury, and may help to account for the propagation of leucocyte emigration to peak numbers during inflammatory reactions.

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