Immature B cells as the target for in vivo tolerance induction

In vitro studies have indicated that immature B cells at a specific stage in clonal maturation are exquisitely susceptible to tolerance induction by antigens and antigen concentrations that have no effect on mature B cells. In order to determine if a similar phenomenon obtains for B cells in vivo, mice were tolerized with DNP-D-GL and their splenic and bone marrow B cells were carefully washed and analyzed for responsiveness in the splenic focus system. The results demonstrate that, whereas the treated mice themselves become rapidly unresponsive to either DNP or TNP on a heterologous carrier, a measurable decrease in the frequency of splenic DNP-responsive B cells occurs only very slowly with a half-life of approximately 2 wk and TNP-responsive splenic B cells are only marginally, if at all, affected. A progressive decrease in DNP-responsive bone marrow B cells is also observed and occurs at a somewhat more rapid rate than the decrease in splenic B cells. The rate of decrease of splenic precursor cells is totally consistent with the normal attrition of mature B cells in the absence of newly generated DNP-specific B cells. Thus, in vivo tolerance, like in vitro tolerance may only eliminate immature B cells as they emerge from their stem cell pool and has no effect on mature resident B cells. This conclusion is consistent with the additional finding that 1 mo after tolerance induction, the majority of remaining DNP-responsive B cells in the bone marrow is found in very early precursors that have not, as yet, acquired their immunoglobulin receptors. Finally, the exquisite specificity of this tolerance induction would be totally consistent with a physiologic role for a clonal abortion mechanism that could specifically eliminate self-reactive B cells while leaving essentially intact the B cell repertoire responsive to non-self determinants.