THE EFFECT OF ANTIGEN ON THE PROLIFERATION OF SPLEEN CELL SUSPENSIONS FROM TOLERANT RABBITS.

DNA synthesis is stimulated when homologous antigen is added to suspensions of spleen cells from previously immunized rabbits. This has been taken to represent the in vitro counterpart of the proliferative response seen in vivo and which leads to the appearance of differentiated cells which synthesize antibody. The results described show that cells from a rabbit made tolerant by neonatal exposure to antigen do not respond to that antigen when challenged in vitro even after an intensive course of immunization. (It should be noted that small quantities of antigen were probably still present in the circulation at the time of sacrifice.) Thus, not only is no antibody synthesized but there is no proliferative response of precursor cells. In addition, it has been shown that simultaneous exposure of the cells to the antigen to which they are tolerant does not affect their response to a second antigen to which they are immune. These findings are consonant with the reports of in vivo studies (1–4) referred to in the introduction and confirm the complete lack of a response at the cellular level in immunologically unresponsive animals.