Alternative pathway of complement in multiple myeloma.

The alternative pathway of complement was studied in 16 newly diagnosed and 2 previously treated patients with multiple myeloma. Functional activity of this pathway was abnormal in 10 of these 18 patients (55%). These abnormalities correlated with depressed levels of alternative pathway components in 3 of 10 patients, but in the remaining 7, no etiology was demonstrated. There was an inverse correlation between activity and concentration of the monoclonal protein. This defect is an additional factor that may predispose patients with myeloma to overwhelming infection.