Enhancement by Monoclonal Anti-Lyb-2 Antibody of Antigen-specific B Lymphocyte Expansion Stimulated by TNP-Ficoll and T Lymphocyte-derived Factors

By using antigen-specific populations of B cells (TNP-ABC) we have demonstrated that the type-2 antigen TNP-Ficoll was capable of initiating B cell proliferation only in the presence of T cell-derived factors. Monoclonal-anti-Lyb-2.1 antibody acted synergistically with a T cell-derived supernatant, as well as with B cell-stimulating factor (BSF-1) to enhance the level of B cell expansion obtained in this in vitro system. This effect of anti-Lyb-2.1 mAB was observed at each day of the antigen-driven B cell expansion and was seen only with B cells purified from strains expressing the Lyb-2.1 allele. The epitope density of hapten on the Ficoll plays a critical role in this process, because Ficoll that is haptenated with low density of hapten was not found to be stimulatory. These results suggest that the Lyb-2 surface molecule influences the antigen-driven B cell growth that is stimulated by type 2 antigens and BSF-1.