PERIPHERAL-BLOOD ANTIBODY-SECRETING CELLS IN THE EVALUATION OF THE IMMUNE-RESPONSE TO AN ORAL VACCINE

Specific antibody-secreting cells (ASC) appear in the blood as a respo nse to oral vaccination in humans. Based on information from animal ex periments, these cells are believed to be migrating to the mucosa. Thi s review summarizes a series of studies aimed at a detailed characteri zation of the ASC response to a prototype oral vaccine Salmonella typh i Ty21a, with respect to its kinetics, Ig-class distribution, antigen specificity, influence of the administration route and nature of the a ntigen, and the corresponding antibody responses in serum. Different v accine formulations as well as dosage schedules are compared, and the response to booster immunization is described. The response manifested by ASC in blood is shown to be independent from serum antibody respon ses. Moreover, it is shown to parallel with the results obtained for p rotection in field trials. Finally, some data on the homing receptor e xpression of these cells are presented, giving further evidence for th e mucosal. homing of these cells. The ASC assay offers a practical mea ns for assessing immune response to oral vaccines in humans. It can be used as a laboratory parameter correlated with protection conferred b y an oral typhoid vaccine. It can even be applied to measure active mu cosal immunity, i.e., protective immunity by showing the relative redu ction of the ASC response to an oral dose of live vaccine.