Two‐dimensional electrophoretic analysis of cryoproteins: A report of 335 samples

Cryoproteins are defined as proteins precipitating at low temperature. Most frequently, the precipitate contains immunoglobulins (Igs), and are therefore called cryoglobulins. Three types of cryoglobulins have been described: type I contains a single monoclonal Ig, whereas type II is a mixture of a monoclonal Ig with polyclonal Igs, and type III is a mixture of polyclonal Igs of different isotypes, most frequently IgG and IgM. Type II and type III are also called mixed cryoglobulins. A new type of cryoglobulins, containing polyclonal IgG associated with a mixture of polyclonal and monoclonal IgM has recently been described after two‐dimensional polyacrylamide gel electrophoresis (2‐DE). This type of cryoglobulin has been called type II–III cryoglobulin. In this study, we report on 2‐DE analysis of 335 cryoproteins from patients with heterogeneous clinical conditions. In 69 out of 335 samples (20.7%), 2‐DE revealed patterns that were inadequate to characterize the cryoproteins. Out of 335 (79.3%) cryoproteins, 266 were identified according to their two‐dimensional patterns: 265 samples contained Igs and were diagnosed as cryoglobulins, and one sample consisted of fibrinogen, and was identified as cryofibrinogen. Among the 265 cryoglobulins, types I, II, and III were observed in 9 (3.4%), 69 (26%), and 116 (43.8%) cases, respectively, whereas type II–III was detected in 71 (26.8%) cases. Eleven of the latter consisted of oligoclonal Igs (IgM in 10 cases, IgA in 1 case) mixed with traces of polyclonal IgG. These cryoproteins were tentatively named type II–IIIvariant cryoglobulins. Taken together, our result clearly show that 2‐DE is a suitable technique to analyze cryoproteins.