Human plasma P component (protein AP): changes during growth and development and evidence for hepatocellular...

A monospecific rabbit antibody to human plasma P component was used in a quantitative immunoelectrophoretic system. The assay readily detected levels as low as 0.3 microgram/ml, the equivalent of 0.008 U/ml of a normal plasma pool. he average coefficient of variation of duplicate determinations from five sets of nine dilution points of normal plasma was 6.6%. Among normal individuals, groups of 50 adults, 24 children, and 43 term and preterm newborns were each significantly different (p less than 0.001) and the level was positively correlated with age. Three fetal samples of approximately 20 weeks' gestation were near the lower limit of detection of the assay. P component levels in selected groups of patients demonstrated a 1.5 fold elevation of the mean level in 15 patients with high erythrocyte sedimentation rates, no difference in the mean level of 23 patients on warfarin or 16 patients with plasma cell dyscrasia or chronic lymphocytic leukemia, and a depression of the mean level to one fourth of normal in 14 patients with alcoholic liver disease. Among the latter, the prolongation of the prothrombin time was correlated with the depression of P component (p less than 0.05). Conditioned media, even after 10-fold concentration, and lysed cell fractions of cultured adult fibroblasts, B and T lymphocytes, and endothelial and smooth muscle cells failed to demonstrate P component. Circulating levels of P component increase during growth and development to adult life and the hepatocyte is the most likely site of synthesis. Although homologous in structure, C-reactive protein levels are distinguished by their marked response to inflammation and their elevation in most of the patients with hepatocellular damage.