Complete and Partial Deficiencies of Complement Factor D in a Dutch Family

A young man suffering from recurrent Neisseria infections was shown to lack detectable serum complement factor D hemo-lytic activity. Addition to the patient's serum of purified factor D to a final concentration of 1;g/ml resulted in full restoration of the activity of the alternative pathway. Using an enzyme-linked immunosorbent assay, it was shown that the patient's serum did not contain measurable amounts of factor D antigen either. The sister, the father, as well as the parents of the mother had factor D levels within the normal range, and the factor D level of the mother was decreased. The capacity of the patient's serum, at concentrations up to 5%, to promote phago-cytosis of Escherichia coli by normal human granulocytes was low when compared to normal serum. Substitution of the pa-tient's serum with purified factor D resulted in a full restora-tion of opsonic activity. This study describes the first complete deficiency of factor D, and demonstrates its possible relation to recurrent Neisseria infections