Class switching is an important process that occurs during the primary immune response, allowing different immunoglobulin classes to be produced. In the primary immune response, IgM is the first class of antibody to be synthesised by an activated B cell. To improve the efficiency of the response to a bacterial or viral infection, class switching will change the constant region to IgG.
IgM is beneficial in the first instance of a response, as it is able to induce inflammation if a parasite is present – encouraging it to leave. IgG is better to target bacterial and viral infections, as it is able to transport throughout systemic circulation and most body tissues. This allows it to efficiently reach the site of infection.