Complement activation is necessary for an adequate immune and inflammatory response to
infections. Activation releases
anaphylatoxins that cause vasodilation, increase vascular permeability, and trigger release of polymorphonuclear neutrophil leukocyte (PMN) lysosomal
enzyme and
oxygen radicals. Under normal circumstances, an orderly progression of such events has a beneficial antimicrobial effect. The same mechanism, however, when uncontrolled, may damage host tissues. To provide information about the clinical importance of such events in
sepsis, different
complement parameters (C3, C4, and the desarginated forms of C3a [
C3a(des)-Arg] and C5a [
C5a(des)-Arg]),
PMN elastase, and
malondialdehyde (a by-product of membrane peroxidation by
oxygen radicals) were measured daily in 26 septic patients and correlated with two objectively assessed and previously validated severity scores (acute physiology and chronic health evaluation [APACHE II] and
Sepsis Severity Score [SSS]). Nonsurvivors (n = 12) had significantly greater and longer lasting complement activation than that in survivors, as reflected by higher levels of catabolic
peptides (C3a(des)-Arg) and lower levels of native
proteins (C3 and C4). C3a(des)-Arg, C3, C4, and the C3a(des)-Arg-C3 ratio were correlated with
Sepsis Severity Scores. Polymorphonuclear neutrophil
leukocyte elastase levels were higher in nonsurvivors and were correlated with C3a(des)-Arg and the C3a(des)-Arg-C3 ratio.
Malondialdehyde levels were significantly higher in all patients than in controls, without, however, any relationship to severity of disease or clinical outcome. Since the higher and more persistent the complement activation and polymorphonuclear neutrophil leukocyte stimulation, the worse the patient's prognosis, we conclude that these mechanisms may be important in the clinical development of
sepsis.