Role of the Thymus in Anti-Hapten Responses in the Rabbit

Division of Serology, Institute of Immunological Science, Hokkaido University Sapporo, Japan (Received for Publication, Nov. 20, 1978) Rabbits thymectomized within 2 months after birth presented a more marked anti-hapten antibody response against DNP-BGG than non-thymectomized control animals. A reduction in anti-hapten response was observed in rabbits injected with allogeneic thymocytes, although it was of short duration. A marked reduction in anti-hapten response was observed in rabbits pre-immunized with the carrier, showing a sharp contrast with an ordinary response observed in the mouse. The results mentioned above seemed to show the possibility that the immunological function of the rabbit T cells might be qualitatively or quantitatively different from that of the mouse T cells. Great progress in the study of the cellular basis of immunity has been made in the past decade, since Miller ll has first reported on the immunological significance of the thymus in 1961. One of the most important advances in cellular immunology may be the classification of immunocompetent lymphocytes into two categories, T and B, which not only perform distinct roles in immunity but also interact with each other in humoral immune responses. Thus, Mitchison2•S) has clarified, using hapten-carrier systems, that T cells recognize carrier portion of the antigen, resulting in the anti-hapten antibody synthesis by B cells which recognize haptenic determinants attached onto the carrier protein. Studies by several investigators on the T-B cooperation in immune responses4S) have been mostly carried out by the use of mice, and those conducted in rabbits were far less easy to find in literatures except a series of studies by Richter and his co-workers935J • The latter fact seems to result from two reasons. Firstly, rabbits are the species difficult to obtain an inbred strain in sufficient numbers and secondly, it is doubtful whether rabbit lymphocytes, especially T cells have the same function as those of mice, because the effect of thymectomy is reported to vary greatly with the species of animals used. According to Burnet's observation), there was no visible effect of neonatal thymectomy in the dog and very little in the rabbit. In addition, Abdou and Richter ) have reported that the antigen-reactive cells of the rabbit (i. e., mouse T cell equivalent) are not originated from the thymus but are normally found in the bone-marrow and the organ source of the rabbit antibody-forming cells remains to be clarified. If this were true, it should be said that the immunological significance of the rabbit thymus and thymus-derived cells is beyond comprehention. Thus, our present study was undertaken to clarify the role of the rabbit thymus in immunity and it was demonstrated that thymectomy of the the rabbit within 2 months after birth resulted in a marked enhancement of the humoral response against DNP.