Role of the thymus in the immune response to sheep erythrocytes in the lizard Calotes versicolor

Abstract

The role of the thymus in antibody response to sheep erythrocytes (SRBC) was investigated in the lizard,Calotes versicolor, by utilizing the experimental models of adult thymectomy and anti-thymocyte serum (ATS) treatment. When thymectomized lizards were treated with high dose regimen of ATS, plaque-forming cell (PFC) response to SRBC was abrogated; however, this response was not altered by the low dose. A definite recovery of anti-SRBC response after ATS treatment occurred in the presence of the thymus. On the other hand the PFC response to SRBC was enhanced one month after adult thymectomy and after low dose ATS treatment. Both low and high doses of normal rabbit serum suppressed the immune response to SRBC and it is suggested that this suppression might be due to antigenic competition. These results indicate that (i) anti-SRBC response is thymus dependent and (ii) there are two kinds of thymus derived cells: one 'helper' collaborating in anti-SRBC response and another 'regulator' governing the magnitude of the response which is involved in antigenic competition. The phylogenetic status on the dual role of the thymus in immune functions has been discussed.