Isolated hapten-binding receptors of sensitized lymphocytes. V. Cellular origin of receptor molecules

Chimeric mice were constructed by injection of thymus cells into nu/nu mice. The thymus cells carried a different immunoglobulin (Ig) heavy chain linkage group than the cells of the recipients. The chimeric animals were then immunized with the hapten (4-hydroxy-3-nitro-phenyl)acetyl (NP) on an appropriate carrier, and NP-binding receptor molecules were isolated from the spleen cells of the animals. Receptor molecules and antibodies were analyzed for the presence of two Ig heavy chain variable region (V_H) markers which are specific for the anti-NP response of mice carrying the Ig^b allogroup, namely the NP^b idiotpye and the heteroclitic fine specificity of hapten binding. Two types of receptor molecules are obtained by our method, those carrying determinants of Ig constant domains (anti-Ig⁺ receptors) and others lacking such determinants (anti-Ig^? receptors). The two V_H region markers were found on anti-Ig^? receptors but not on anti-Ig⁺ receptors and humoral antibodies when the T cells in the chimeric mice carried the Ig^b allogroup, whereas the B cells were Ig^a/a. Conversely, anti-Ig⁺ receptors and humoral antibodies but not anti-Ig^?receptors, expressed the two markers when the B cells of the chimeras carried the Ig^band the T cells the Ig^a allogroup. From these results and previous data showing that anti-Ig^? receptors are enriched together with T lymphocytes and anti-Ig⁺ receptors together with B cells, we conclude that the V_H-bearing anti-Ig^? receptors are not only present on T cells, but are indeed synthesized by these cells.