Initial vs long term. Generally we see IgM as the initial antibody that we make in response to an infection. Igg is the antibody that provides long-term protection.
IgG and IgM differen. There are five primary immunoglobulins, igg, ga, igm, igd, and ige. Although there overall structure is similar there quantities and functions are different. Igg is the most important from a protective standpoint. Igm is developmental the first immunoglobulin identified in as immature creature as the lamprey. Igg is also the only immunoglobulin that can and may need to be replaced, ivgg or scgg.