DSC investigation of IgG thermostability in blood plasma of patients with myeloma G

We conducted differential scanning calorimetry (DSC) research of blood plasma/serum of 66 patients with myeloma G (MG), characterized by high levels of IgG and low levels of IgM and IgE. Our findings demonstrate that DSC curves can be classified into two main subgroups, distinguished by curve profiles and melting temperatures (T_m) during the main stage of IgG transition. In the first group, the plasma/serum of 26 patients had a one-stage intense transition of IgG with T_m = 77.5 ± 2.5 °C. In the second group, the plasma/serum of 29 patients had two transition stages of IgG with an intense peak around T_m = 73.0 ± 2.5 °C and a minor peak with T_m = 78.5 ± 2.0 °C. A wide range of IgG melting temperatures (70.5–80.0 °C) indicated the presence of different mutations in the composition of IgG (IgG1, as per our consideration) within the plasma/serum of MG patients, contributing to increased thermal stabilization. Specifically, the one-stage transition of IgG can be attributed to mutations in the CH2 domain and Fab fragment, initiating an increase in their melting temperatures and shifting towards higher temperatures, overlapping the CH3 domain melting. The two-stage transition may result from a shift towards higher temperatures of the mutated CH2 domain only, accompanied by simultaneous melting of the Fab fragment. We propose that, with a sufficient amount of experimental data, the DSC method can serve as a rapid and secure approach for monitoring MG and detecting IgG1.