What is the difference between IgG4 and C3d?

There are four subclasses of Immunoglobulin G. IgG4 subclass antibodies are connected to a protective response in the Complement pathway of the innate immune system. The body creates IgG4 antibodies in response to an antigen to which the body wants to prevent a subsequent inflammatory response. The rise in food-specific IgG4 may be an initial response to reduce the effect of IgE-mediated disease, but may ultimately result in a pro-inflammatory process in susceptible hosts. In contrast, C3d is a complement protein that increases the rate of enzyme reactions. Reaction to the sensitive food may worsen if complement C3d activation is present. The C3d protein attaches to the antigen and can amplify the immune response. This increases the inflammatory potential of IgG. In general, IgG4 helps reduce inflammation while C3d serve to amplify inflammation. For more information, see the attached Food Sensitivity IgG4-C3d One Pager.