C3b inactivator deficiency: Association with an alpha-migrating factor H

Abstract

Complete absence of Factor I (C3b inactivator) was found in the serum of a 3-year-old boy with recurrent polytope bacterial infections. Analysis of the complement (C) components of the patient's serum showed that while serum levels of the earlier C components (C1q, C1r, C1s, C4, and C2) were within the normal range, levels of C3, C5, Factor B, and properdin were decreased significantly. Factor H (β₁H) was also decreased and, by crossed immunoelectrophoresis, migrated to the alpha region (H_α). C-dependent biological functions such as chemotactic activity, opsonic factors, immune adherence inhibition, and intracellular killing of bacteria were defective. The patient has been treated with fresh frozen plasma (10 ml/kg body weight) every 4 weeks for 2 years. Most of the C-derived biological functions improved, and Factor H regained beta electrophoretic mobility (H_β) following plasma infusion. During the period of treatment, the child has been free of bacterial infections. Mild anaphylactic reactions to the plasma occurrred on two occasions; the other 22 infusions were well tolerated.