The normal occurrence of two molecular forms of the eight complement component (C8) and their concentrations in a family with C8 deficiency.

A haemolytically inactive alpha-mobile complement C8 component was identified by crossed immunoelectrophoresis in a 27-year-old male with recurrent meningococcal infections and absence of complement mediated serum haemolytic activity. The patient's serum/plasma contained no demonstrable normal C8. C8 inhibitor activity was not demonstrable in his serum and the alternative activation pathway appeared to be intact. Serum from the proband's parents and both siblings had normal total haemolytic complement activity and they were without symptoms. However, both the normal and the haemolytically inactive C8 protein were demonstrable in their sera. Their normal C8 concentrations were less than one-half of the normal C8 mean value and distinctly below the lowest value found in ten healthy persons. The concentration of the inactive C8 component in the proband's serum was roughly 1 . 5 times higher than that of the other family members, whereas its concentration in sera of the family members was between 1 . 8 and 2 . 5 times the highest concentration found in ten healthy donors, all of whom also had an alpha-mobile C8 in measurable quantities.