The role of T and B antigen-binding cells in the immune response to sheep erythrocytes in the lizard, Calotes versicolor.

Our previous studies in the lizard, Calotes versicolor showed that low doses of sheep erythrocytes (SRBC) induced bimodal rosette-forming cell (RFC) response, the first RFC peak appearing on the 2nd day and the second on the 10th day after immunization. In the present study, the type of lymphocytes involved in rosette formation has been analysed with reference to their role in the immune response to sheep erythrocytes. One month after adult thymectomy the formation of the early but not the late rosettes was suppressed. The early RFC were sensitive to the in vitro blocking and cytotoxic activity of rabbit anti-lizard thymocyte globulin (ATG), but not the late rosettes. The interrelationship between these two populations has been studied using cyclophosphamide (Cy) and anti-SRBC antiserum. The development of the early RFC was suppressed when Cy was injected with antigen. However, late RFC (B-RFC) were not detected when the drug treatment was postponed to the 7th day of immunization. The absence of any one RFC peak resulted in the inhibition of plaque-forming cell (PFC) response. Thus, the development of early RFC and late RFC occurs independently, although both are required for effective antibody production. The anti-SRBC antiserum inhibited the formation of RFC and PFC responses, when injected along with low doses of SRBC. When antiserum was given 3 days after immunization, both RFC responses occurred to the normal level, even though PFC response was suppressed, however, when the treatment was delayed up to 6 days normal PFC response occurred. Thus, the presence of antigen in the system for up to 6 days is needed for antibody response. The results indicate the sequential appearance to T and B antigen-binding cells in the spleen of the lizard and their interrelationship in antibody production to sheep erythrocytes.