The IgG4 subclass is associated with a low affinity antibody response to tetanus toxoid in man.

The amount and relative affinity of antibodies to tetanus toxoid were measured, following immunization, in patients with chronic or recurrent acute chest infections and in healthy controls. The responding patients and controls produced similar amounts of antibody and, although antibody affinity was higher in the controls compared to the patients, the differences were not significant. Most individuals (65%) produced antibody of the IgG1 subclass with little or no IgG4 antibody, but in the remainder antibody was either predominantly IgG4 (29%) or equally distributed between the IgG1 and IgG4 subclasses (6%). Antibody affinity was significantly lower in both patients and controls producing IgG4 antibodies compared to those with a predominantly IgG1 response, and antibody affinity increased with the amount of IgG1 antibody present. These results provide preliminary evidence of an association between low antibody affinity and the IgG4 subclass in man.