The specific direct interaction of helper T cells and antigen-presenting B cells.

Cell couples have been formed by mixing an antigen- and Ia-specific cloned helper T-cell line with a B-cell hybridoma presenting the antigen. By immunofluorescence observations, we have shown that the microtubule-organizing center (MTOC) inside the helper T cell, but not in the bound antigen-presenting cell, becomes oriented to face the area of specific cell-cell contact. This MTOC orientation is antigen- and Ia-specific, and thus provides direct evidence for the specific interaction of a helper T cell with a B cell. It is presumed that the function served by this MTOC orientation, which is accompanied by the coordinate reorientation of the Golgi apparatus, is to target Golgi apparatus-derived secretory vesicles, containing putative lymphokines and/or growth factors, from the helper T cell directly to the antigen-presenting cell.