Immunochemical Characteristics of Half-Molecule IgG Presumed to Lack the CH2 Domain

Half-molecule immunoglobulins are low-molecular-weight abnormal immunoglobulins composed of one defective heavy chain (H chain) and one light chain (L chain) of normal molecular weight.

The molecular weight of the low molecular weight IgG was determined using SDS-PAGE and immunoblotting with patient serum. To prove that the low molecular weight IgGs were L-chain and deficient γ-chain, SDS-PAGE was used to cut out and reduce the entire gel of unreduced, migrated proteins. Then, a second SDS-PAGE was run.

The low molecular weight IgG component was found to consist of normal molecular weight κ chains (32 and 29 kDa) and defective γ chains (37 and 38 kDa). Low molecular weight IgG did not react with anti-γ-CH2 domain antibodies.

The low molecular weight ɤ chain was also found to be a half-molecular IgG with a CH2 domain deletion, as inferred from the reactivity of the antibody.