Studies on the human immune response to tetanus toxoid

Two aspects of the human inriune response to tetanus toxoid were investigated, vis: the kinetics of the response of pregnant females to tetanus toxoid imnunization with respect to the immunity conferred on their babies; and the in vitro lymphocyte response to tetanus toxoid of reactors to tetanus vaccination. Variables affecting the techniques for measuring the humoral immune response to tetanus toxoid were determined, and a method for antitoxin titration was devised which required only a small volume of serum. Antitoxin determinations in cord sera collected at delivery indicated the relation between timing of tetanus toxoid injections in the mother and the development of an acceptable level of protection in the babies. Analysis of the cord/maternal antitoxin ratios showed that active transport of maternal antitoxin to the foetus can occur, and a possible mechanism for this is discussed. The transplacental passage of tetanus toxoid itself was investigated by the use of an indirect insminofluorescence technique for the detection of tetanus-specific IgM in cord sera. No specific IgM was found in the cord sera, however, but assays for tetanus-specific IftM in maternal sera indicated that this inmunoglobulin is often produced in response to second injections of tetanus toxoid. Lymphocyte reactivity in vitro was determined by lymphocyte transformation in the presence of tetanus toxoid and PHA, as measured by the uptake of tritiated thymidine. Only a few of the severe reactors showed any evidence of an increased in vitro response to tetanus toxoid, but a clearcut inverse relation between age and lymphocyte reactivity to tetanus toxoid was demonstrated. Such an age-related decline in lymphocyte reactivity to a specific antigen in vitro has not been previously reported apparently. The relevance of this finding to current immunological theories of ageing is discussed.