Which of the following is not a distinguishing factor between IgM and IgG?

Kappa and lambda chains are immunoglobulin light chains and are present in both IgM and IgG antibodies. While IgM and IgG are indeed distinguished by various factors, the type of light chain (kappa or lambda) does not serve as a distinguishing feature between the two classes of immunoglobulins. Both isotypes can be composed of either kappa or lambda light chains, meaning that this characteristic does not help differentiate between IgM and IgG.

In contrast, factors such as complement binding, avidity, and molecular weight do play significant roles in distinguishing IgM from IgG. IgM has a higher molecular weight due to its pentameric form, while IgG is predominantly a monomer. Additionally, IgM has higher avidity because of its multiple binding sites and is typically more effective in complement activation compared to IgG, which has a different mechanism of action in immune response. Understanding these distinguishing features is essential for professionals in histocompatibility and immunology.