Primary and secondary antibody responses to tetanus and diphtheria antigens

Antigen is administered at the time indicated on the X-axis. No unit of time is provided since the course of response varies by route of administration, antigen dose, and how rapidly the antigen is cleared from the body or persists. Response times range from 2 to 4 weeks for many protein and glycoprotein antigens not associated with ongoing infection. In the primary response, there is an initial lag period, and then IgM is produced initially, followed later by IgG. In the secondary response, there is a much shorter lag period. The initial rise in antibody production is more rapid, and the total amount produced is greater than in the primary response. While IgM antibodies are also produced, the IgG isotype is predominant, and IgG antibodies have a higher affinity for antigen.