The donor cell type controls anti-hapten (fluorescein isothiocyanate) primary antibody response to hapten-modified syngeneic cells.

Hapten (fluorescein isothiocyanate, FITC)-sensitized syngeneic red blood cells (FITC-RBC) are exceptionally active for induction of anti-hapten primary antibody response, and FITC-modified syngeneic spleen cells depleted of RBC (FITC-SSC) are not immunogenic [4]. The present study has demonstrated that FITC-SSC injected simultaneously with FITC-RBC inhibit partially the anti-FITC response to the latter. Either the immunogenicity of FITC-RBC or the response-inhibiting activity of FITC-SSC was increased as the concentration of hapten-sensitizing cells was raised from 0.005 mg/ml to 2 mg/ml. The inhibition of anti-FITC response by FITC-SSC strictly required live donor cells, but was not dependent on T-cell activity of either the donor or recipient. Neither FITC-thymocytes nor the FITC-T-cell-rich fraction of SSC showed a definite activity for inhibition, whereas the FITC-B-cell-rich fraction of SSC acted very effectively. These results suggest that the primary anti-hapten antibody response to hapten-modified syngeneic cells is primarily controlled by antigen-bearing live donor cells of different cell types.