Specific B lymphocytes efficiently pick up, process and present antigen to T cells.

To study the nature of the antigen bridge between specific B and T lymphocytes we have isolated from the same donor clones of human T cells and EBV-transformed B cells specific for tetanus toxoid (TT). We found that TT-specific B cells are extremely efficient in presenting TT (but not an unrelated antigen) to T cells, as they can trigger T cell proliferation in the presence of only 10(-12) M TT, a concentration that is approximately 10(4) times lower than that required for presentation by conventional antigen-presenting cells such as macrophages or non-specific B cells. The high avidity of the interaction between specific B and T cells is reflected by the resistance to inhibition by antibodies against the T4 antigen. Experiments with fixed and chloroquine-treated B cells show that the role of surface antibodies is limited to the uptake of antigen and that in order to obtain presentation, the antigen has to be internalized, processed and subsequently displayed on the cell surface, where it becomes available for T cell recognition in an MHC-restricted fashion.