Subclasses of the most frequent G immunoglobulins in patients diagnosed with monoclonal gammopathy of undetermined significance (MGUS) and multiple myeloma (MM) in relation to their accompanying light chain.

Abstract

Introduction: Based on the structural differences of their heavy chains, IgGs can be classified into four subclasses,
each with different physicochemical, biological and immunological properties. B-cell proliferative disorders
such as multiple myeloma (MM) and monoclonal gammopathy of undetermined significance (MGUS)
are associated with their production. Objectives: To characterize the type of IgG subclass in patients with MGUS
and MM, and its association with the accompanying light chain as a parameter of diagnostic and prognostic
importance. Materials and Methods: A total of 154 patients with MGUS and MM classified by the band/monoclonal
component of the IgG subclass and accompanying light chain were studied. A serum proteinogram by
capillary electrophoresis, typing of the clone expressed by immunofixation in serum, and quantification of IgG
subclasses by nephelometry were performed. Chi square (X2) and Fisher’s statistical methods were used. Results
were considered statistically significant at p <0.05. Results: The IgG1 subclass was the main one in both
disorders. The tendency of IgG1,2 and IgG4 was greater in MGUS than in MM, whereas the opposite was observed
for IgG3. The light chain prevalences were similar, with no statistically significant differences (p = 0.41; 0.43;
0.74 and 0.85 for MGUS and p = 0.72; 0.41; 0.33 and 0.24 for MM). Conclusions: The tendency of IgG1 is due to
chronic stimulation with Ag, which underlies the onset of MGUS and MM. The differences in the expression of the
remaining subclasses were due to the pathogenic potential of each of them.