A novel mass spectrometric-based proteomic approach challenges the current paradigm on cryoglobulin typing in the diagnostic laboratory

Abstract

Cryoglobulins precipitate out of serum at temperatures lower than 37°C and can have serious clinical manifestations. They may be associated with haematological malignancies, chronic infections and autoimmune diseases. Traditional typing of cryoglobulins use the Brouet classification, depending on the presence or not of rheumatoid factor activity: type I (monoclonal immunoglobulin with no rheumatoid factor), type II (mixed cryoglobulin with monoclonal rheumatoid factor) and type III (mixed cryoglobulin with polyclonal rheumatoid factor). Current methods used to type cryoglobulins include electrophoresis and immunofixation. We describe a novel, streamlined workflow of cryoglobulin analysis using mass spectrometry (MS) to characterise the proteomic signatures [heavy chain complementarity-determining region 3 (HCDR3) regions] of cryoglobulins. This provides an extension to traditional immunochemical methods of analysis and offers increased sensitivity; monitoring capacity by HCDR3 regions at the amino acid level; and clinical applications. Outstandingly, MS analysis offers predictive value by detecting the presence of pathogenic clonotypes before the onset of clinical manifestations. We highlight its applicability and benefits through clinical cases, demonstrating the greater ability to molecularly characterise cryoprecipitates in a similar turn-around time to current methodology. Work to establish clinically relevant libraries of antibody clonotypes is currently underway.