Biochemical Abnormalities of the Third Component of Complement in Neonates

Abstract

ABSTRACT. The third component of complement, C3, is of central importance as an opsonin in the nonimmune host. Although gestational deficiencies in C3 levels are well recognized in neonates, defects in complement-mediated functions have not in every case correlated with low levels of complement proteins. Because opsonic functions of C3 are mediated through a reactive thiolester bond, we hypothesized that a biochemical dysfunction at this active site could explain the newborn's predisposition to infection, even with relatively normal C3 levels. We therefore examined the biochemical integrity of the C3 thiolester in an assay independent of all other complement proteins. As measured by ELISA, mean C3 levels from 44 neonates (24-43 wk) were significantly lower in infants < 30 wk gestational age (0.79 f 0.13 mg/mL) than in full-term newborns (1.19 +1 0.27 mg/ml, p < 0.05). Furthermore, biochemical reactivity of the thiolester bond, as measured by incorporation of the radiolabeled nucleophile, methylamine, correlated significantly with gestational age ( r = 0.45, p < 0.01). Functional C3 was defined as the product of thiolester reactivity and C3 level; 9/11 premature and 2/ 17 full-term infants had levels of functional C3 which were less than 50% of the adult norm. Structural analysis of neonatal C3 revealed the two-chain structure in all neonates; four neonates had an additional band at 205 kD which may represent an impairment in posttranslational processing of a precursor molecule. We conclude that defects in thiolester reactivity may constitute a newly identified mechanism for the newborn's susceptibility to infection. (Pediatr Res 26: 116-120, 1989) Abbreviations PAS, pooled adult serum CH3NH2, methylamine Sepsis is a leading cause of morbidity and mortality in neonates, with premature infants affected more frequently than fullterm newborns (I). This predisposition to infection is ascribable, at least in part, to age-related defects in host defense (2, 3). Primary among humoral defenses are the complement proteins, which serve as opsonins for common neonatal pathogens such as the group B Streptococcus or the K1 capsular serotype of Escherichia coli (4,5).

Complement Activation in Newborn Infants with Early Onset Infection

“…The apparently sufficient C3-activation does not, however, allow any conclusion on further functional o aspects. Zach et al (39) reported defects in thiolester reactivity . Recently, it has been shown that supplemental C9 enhanced the capacity of neonatal sera to kill a pathogenic strain of Escherichia coli (40), suggesting that C9 deficiency may be one of the factors that predispose neonates to develop E. coli -sepsis.…”

Amniotic Fluid Levels of the Third Component of Complement

“…Therefore, unlike maternally derived IgG, C3 quantitated in cord blood serum is directly synthesized by the fetus. The hepatocyte is the principal source of serum C3, and the human fetal liver begins to synthesize C3 at 11-14 weeks of gestation [ 8 , 9], C3 concen trations in neonatal serum are lower in pre term infants (24-29 weeks gestation) than in term newborns (37-43 weeks gestation) [1], Notarangelo et al [2] reported that C3 levels in neonatal serum demonstrate a positive cor relation with increasing gestational age from 31 to 42 weeks gestation [2], Gestational age (weeks) Fig. 1.…”

“…C3 serves as an opsonin for common neonatal pathogens such as the group B Streptococcus or the K1 capsular serotype of Escherichia coli. Levels of C3 in cord blood serum are significantly lower in preterm infants than in full term newborns [1,2], Previous studies have dem onstrated that C3 is also present in amniotic fluid, and that amniotic fluid has opsonic capabilities [3][4][5][6]. We undertook this study to determine the relationship between C3 levels in amniotic fluid and gestational age.…”

Pentoxifylline Inhibits Tumor Necrosis Factor-Alpha Induced Synthesis of Complement Component C3 in Human Endothelial Cells

“…The endothelial cells were initially grown to confluence in 25 cm 2 tissue culture flasks using endothelial growth media 2 (EGM-2, BioWhittaker) and then trypsinized and plated into 75 cm 2 tissue culture flasks to determine the effects of TNF and PTX on C3 mRNA C3 Determination by ELISA C3 concentrations were measured in duplicate in HUVEC supernatant using a modification of the method previously described by Zach et al 15) Briefly, 96-well microtiter plates were coated with 0.1 ml of a 1 : 400 dilution of goat antihuman C3 (Atlantic Antibodies) in carbonate/bicarbonate buffer (pH 9.6), incubated overnight at 4°C, and washed 3 times with 0.05% Tween 20 in PBS. Cell culture supernatant samples (0.1 ml) were added to duplicate wells and incubated for 1 h at 37°C.…”