Serum immunoglobulin-lipid complexes in plasma cell dyscrasia

Immunoglobulin-lipid complexes (SILC) are found in the serum of all patients with monoclonal gammopathy. Fractionation by density gradient ultracentrifugation, Sephadex G-200 chromatography and Sepharose protein A affinity, followed by extensive immunoassaying for immunoglobulins and lipoproteins, does not confirm the accepted assumption that SILC are immune complexes between monoclonal immunoglobulins and lipoproteins. Lipid extraction of monoclonal fractions isolated on protein A columns followed by thin-layer chromatography shows a lipid pattern characteristic of the one found in cellular membranes. It is proposed that SILC are hydrophobic complexes between immunoglobulins and lipids, as described in membranes of B lymphocytes.