54 RECURRENT INFECTIONS OF RESPIRATORY TRACT WITH GRAMBACTERIA DUE TO OPSONIC DEFECT IN FACTOR D‐DEFICIENCY

Abstract

Three siblings, two boys and one girl, suffered from recurrent infections of the respiratory tract, almost exclusively caused by H.influenzae, from todler's age onwards. Non-immunological causes, e.g. immotile cilia syndrome, were excluded. Extensive testing of the immunological defence capacities revealed consistently an impaired alternative complement pathway(AP50) and serum levels of all major immuneglobulin classes at the lower borderline of normal. There was no absence of one of the IgG subclasses. The impaired AP50 was due to a functional deficiency of complement factor D. However, antigen factor D, as determined by a sandwich ELISA technique, revealed normal levels. Opsonic activity of serum from the three patients for S.aureus was similar to that of serum from healthy adults, but E.coli, opsonized by the patients' sera were ingested at abnormally decreased rate. It is hypothesized that to combat Gram− infections C3b-mediated opsonisation is attained via the alternative pathway in case insufficient IgG antibodies are available. The latter might have been the case in these children, in association with an impaired alternative pathway-mediated opsonisation. The discrepancy between the antigenic and functional factor D levels needs further investigation.