Opsonic activity of myeloma immunoglobulins (MM-Ig).

Patients with MM are at an increased risk for life-threatening bacterial infections, primarily by organisms that require opsonization for interaction with granulocytes. In the present study we used a neutrophil chemiluminescence (CL) assay of opsonization to explore the opsonic activity of MM-Ig for zymosan particles. Particles were treated with serum lacking in Ig to explore the contribution of Ig to zymosan opsonization. This serum was found to have 69 +/- 2.6% (X +/- SEM) of the opsonic activity of normal serum (P less than .001). Normal serum concentrations of normal IgG, MM-IgG, and MM-IgA all lacked opsonic activity for zymosan. However, when particles were treated with Nl-IgG, MM-IgG, or MM-IgA as well as complement, normal opsonic activity was generated. Increasing the concentration of the Ig to stimulate MM serum did not inhibit this opsonic activity. Thus both MM-IgG and MM-IgA can function as normal, nonspecific opsonins.