Effects of immunoglobulin structure on Fc receptor binding: a mouse myeloma variant immunoglobulin with a gamma 2b-gamma 2a hybrid heavy chain having a complete gamma 2a Fc region fails to bind to gamma 2a Fc receptors on mouse macrophages.

We report here the primary structure of an immunoglobulin heavy chain synthesized by ICR 16, a variant of the MPC 11 mouse myeloma cell line. The ICR 16 heavy chain is a gamma 2b-gamma 2a hybrid, consisting of the CH1 domain of gamma 2b and the hinge, CH2 and CH3 domains of gamma 2a subclasses. The genetic mechanism by which ICR 16 occurred may be recombination, based on homologies in both coding and intervening sequences in gamma 2b and gamma 2a constant region genes. Although the Fc fragment of ICR 16 is completely gamma 2a-like and has been shown to bind to gamma 2a Fc receptors on mouse macrophages, the intact H2L2 molecules is unable to do so. Such an observation underscores the crucial role that conformation may play in the ability of immunoglobulins to carry out biologic functions.