Primary and secondary antibody responses to tetanus and diphtheria antigens

Antigen is administered at the time indicated on the x-axis. Time on the x-axis is not marked with units, since the course of the response will vary greatly depending on the dose of antigen, the route of administration, and whether the antigen persists in the body or is rapidly cleared. For many protein or glycoprotein antigens not associated with an ongoing infection, the time course of the response ranges from two to four weeks. In the primary response, there is an initial lag period, and then immunoglobulin M (IgM) is produced initially, followed later by immunoglobulin G (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. In addition, there is a predominance of the IgG isotype (although IgM antibodies are produced as well), and the antibodies have higher affinity for antigen.