The analysis of the complement activation product SC5 b-9 is applicable inneonates in spite of their profound C9 deficiency

Native complement factors and complement activation products were measured in healthy neonates (n = 72) and in a group of infants with premature prolo nged rupture of the membranes (PPROM) without sepsis (n 10). Vitronectin co ncentration in normal cord blood was not correlated with gestational age, a nd the median value was 86.0 % of adult values. This was markedly higher th an other native complement factors studied (factor B: 35.9 %, C4: 45.1 %, C 3: 56.2 %). The concentration of C9 showed a positive correlation with gest ational age and was very low, 10.8 % of normal adult values in cord blood a nd 8.3 % in the patients. Fifteen percent of the neonates had C9 levels low er than 2 % of adult values. The complement activation products Bb and SC5b -9 were significantly elevated in the patients (159 % and 130 % of control values, respectively), indicating alternative and terminal pathway activati on. In contrast, C4 be and C3 he levels were not increased. The maximum amo unt of SC5 b-9 which could be generated in the neonatal sera by cobra venom factor was highly correlated with C9 concentration (r(s) = 0.86, p = 0.000 1) The profound C9 deficiency found in neonates is correlated with gestatio nal age, limits the capacity to form bacteriolytic C5 b-9 (m) and may predi spose for severe invasive bacterial infection. The plasma level of SC5 b-9 under normal conditions was very low, only 0.3% (0.1 %-3.0 %) of the values obtained after CVF activation of the same samples. Therefore, we suggest t hat the analysis of SC5 b-9 is applicable also in neonates, in spite of the ir extremely low C9 levels.