CLEAVAGE OF HUMAN-COMPLEMENT COMPONENT C5 BY CYSTEINE PROTEINASES FROM PORPHYROMONAS (BACTEROIDES) GINGIVALIS - PRIOR OXIDATION OF C5 AUGMENTS PROTEINASE DIGESTION OF C5

Since severe periodontitis is characterized by an acute inflammatory r esponse with cellular infiltration and microbial overgrowth, plasma pr oteins could be exposed to both proteinases and oxidants released from the granulocytes, as well as to proteinases from the microorganisms. When human complement component C5 was digested by cysteine proteinase s (i.e. gingipain-R and gingipain-K) from Porphyromonas gingivalis, li mited cleavage of the C5 molecule was observed. If C5 was first oxidiz ed by hydroxyl radicals, these gingipains converted modified C5 to fra gments that exhibited significantly greater pro-inflammatory activity than did digests of unmodified C5. After cleavage of oxidized C5 by gi ngipain-R, the digest exhibited measurably greater neutrophil enzyme r elease and chemotaxis of human polymorphonuclear leukocytes (PMNs) com pared with the activities of unoxidized C5 digests. Gingipain-K genera tes virtually no polarization or chemotactic activity of human PMNs fr om C5, nor is enzyme release stimulated by these C5 digests. However, when oxidized C5 was digested by gingipain-K, human PMNs were stimulat ed for polarization, chemotaxis and enzyme release indicating that an active fragment had been generated. Proteolysis of oxidized C5 evokes greater neutrophil activation than does proteolysis of unoxidized prot ein, a fact which supports the hypothesis that oxidation and proteolys is may be coupled to enhance the destructive effects of the inflammato ry process. These results, in which digests of both oxidized and unmod ified complement component C5 were evaluated, support the general conc ept that oxidation and proteolysis may participate cooperatively in am plifying both the severity and duration of the inflammatory reaction.