Degradation of Soluble Immunoglobulin Aggregates in Vitro by Monocytes from Normal Subjects and from Patients with Systemic Lupus Erythematosus

The capacity of human peripheral monocytes to degrade soluble immunoglobulin (IgG) aggregates (AIgG) was studied in vitro. Under serum-free conditions peripheral monocytes from normal donors were able to degrade soluble AIgG in a linear and time-dependent fashion. Addition of fresh human or fresh guinea-pig serum to the incubation mixtures caused a marked increase in degradation of the amount of soluble AIgG available. The stimulatory effect of fresh serum was complement-mediated, because it was abolished by heat treatment of the serum and was not seen when C4- or C3-deficient sera were tested. Functional inactivation of C3 receptors on the phagocytes by trypsin also abolished the complement-mediated stimulation, suggesting cooperation between Fc and C3 receptor in degradation of soluble AIgG. No significant differences were found between monocytes from normal donors and those from patients with systemic lupus erythematosus, as far as degradation is concerned in the presence of complement.