ISOTIPIC CHARACTERIZATION OF IGA PARAPROT EINS - ASSOCIATION WITH OTHER CLINICAL AND ANALYTICAL DATA

A study was conducted to investigate the relationships between the cha racteristics of IgA paraprotein and the clinical findings in a group o f 196 patients. In 19 cases IgA paraprotein was associated with anothe r monoclonal immunoglobulin (IgG or IgM); the other 177 patients had a single IgA paraprotein; 145 of them corresponded to multiple myeloma (MM) and the other 32 to other diagnostics. Class and type of paraprot eins were identified by immunoelectrophoresis and subclass by an enzym e-immunoassay specifically developed for this study. The degree of pol ymerization of the protein was determined by gel filtration; quantitat ion of monoclonal IgA and policlonal IgG and IgM was obtained by kinet ic nephelometry. Out of 196 paraproteins, 96.4% were classified in IgA 1 subclass and only 3.6% in IgG2. In 14 cases, all of them diagnosed w ith MM, monoclonal IgA in serum was associated with Bence-Jones protei n; in more than 78% of them light chains corresponded to type lambda, whereas type kappa predominated (over 60%) in cases without Bence-Jone s protein in serum. Significantly higher serum levels of monoclonal Ig A were associated with the diagnosis of myeloma, with type kappa parap roteins, and with the presence of Bence-Jones protein in serum. The ca ses with two paraproteins (IgA and IgG or IgM) had significantly lower serum levels of IgA, with comparable levels of total paraprotein (the addition of both monoclonal immunoglobulins). Serum levels of policlo nal IgG and IgM, which appeared decreased in cases of MM, were normal in cases with other conditions. In all these cases, monoclonal IgA sho wed a monomeric character, whereas relevant amounts of polymerized IgA paraprotein was found in almost a third Dart of myeloma cases, partic ularly in those with higher serum levels of paraprotein, or when parap rotein belonged to type kappa. The 5 IgA2 paraproteins analyzed had a polymeric character. In conclusion, a detailed, both qualitative and q uantitative, analysis of IgA paraproteins can lead to a better knowled ge of conditions associated with their presence and at the same time p rovides useful data for a clinical evaluation of patients.