Oral Immunization and Production of Coproantibody in Human Volunteers

Abstract

A group of nine human volunteers received daily doses of oral cholera vaccine for 4 weeks. At the end of this period, seven (78%) showed appreciable antibody titers in fluid stools and/or duodenal fluids. Coproantibody could be maintained in these volunteers for 12 weeks (i.e., the length of the experiment) by a single weekly oral dose of vaccine.A primary course of daily oral doses for 2 (rather than 4) weeks was less effective in inducing coproantibody. Completely ineffective was a primary course of twice-weekly (rather than daily) oral doses for 4 weeks. A tentative schedule for induction of coproantibody in man by oral vaccine may therefore be formulated which consists of a primary course of one daily dose for 4 weeks, followed by one weekly dose for as long as coproantibody must be maintained. Oral vaccination is the only known method for maintaining coproantibody in man.Coproantibody titers in the orally immunized volunteers were of the same order of magnitude as those found previously after parenteral vaccination, in spite of the fact that 75 times higher serum antibody titers were induced by parenteral vaccine. Consequently, coproantibody stimulated by oral immunization appears to be produced in the intestine rather than being derived from serum antibody.Coproantibody titers in the duodenum of fasting volunteers were low, but increased sharply after a test meal of butter. Antibody titers in duodenal fluids were unrelated to the presence of bile. In many volunteers duodenal antibody titers were of the same order of mangitude as fecal titers, suggesting that release of antibody into the lumen occurs not only in the duodenum but also in lower portions of the intestinal tract. Presence of coproantibody in duodenal fluids was unrelated to the presence of bile pigments.