Assessment of naturally occurring covalent and total dimer levels in human IgG1 and IgG2.

•Low levels (<1%) of dimer can be measured on endogenous human IgG1 and IgG2.•About 0.4% of IgG2, but little IgG1, is in a covalent dimer form.•Covalent IgG2 dimer can be generated under physiological redox conditions.