Demonstration of thymus-independent immune system in Xenopus laevis. Response to polyvinylpyrrolidone

Larvae of Xenopus laevis were thymectomized at stage 45 (4 days old), and raised beyond metamorphosis. Thymectomized toads, when injected with polyvinylpyrrolidone (PVP), produced the same titres of antibodies as non-thymectomized animals, providing strong evidence that the thymus-independent immune response is present in this anuran. Antibodies were of exclusively high molecular weight, heat-stable, and 2-mercaptoethanol sensitive. After immunization, lymphoid accumulations were evident in the splenic white pulp of both thymectomized and non-thymectomized toads, but in the red pulp the accumulations were prominent only in non-thymectomized toads.