Fab-arm exchange

636 mAbs Volume 4 issue 6 Immunology and structural biology are highly complex fields of study in which mechanisms and inter-relationships are often not easily understood. It is therefore quite common to use metaphors to make knowledge gained accessible to experts and non-experts alike. Thus we, for example, all know the antibody as a Y-shaped protein with two arms and a tail and we understand the specificity of antibodyantigen binding as a key-into-lock interaction. Are these metaphors strictly correct? No, of course not. Nevertheless, they are well-recognized and serve to provide some immediate and general understanding of key features. When faced with the challenge of designing a simple descriptor or metaphor for the process leading to the exchange of human IgG4 “half-molecules,” we discussed various options with experts in the field and came up with the term “Fab-arm exchange.” The phrase is simply meant to highlight the functional consequence of this mechanism, i.e., the exchange of antigen-binding parts between parental antibody molecules leading to novel binding combinations in the product. Professor Pandey argues in his letter that Fab-arm exchange is a misnomer and should be changed to IgG4-arm exchange with the argument that allotypic differences are ignored. Apart from the fact that, seen from Pandey’s view, the phrase IgG4-arm exchange suffers from similar weaknesses as the original (and should be termed IgG4-arm-and-tail exchange instead), clearly we disagree. This is not Fab-arm exchange What’s in a name?